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Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs in the abdomen (in internal structures called fat bodies), under the skin and, in some salamanders, in the tail. There are two kidneys located dorsally, near the roof of the body cavity. Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. Urinary bladder.
Most aquatic and semi-aquatic amphibians have a membranous skin which allows them to absorb water directly through it. Some semi-aquatic animals also have similarly permeable bladder membrane. As a result, they tend to have high rates of urine production to offset this high water intake, and have urine which is low in dissolved salts. The urinary bladder assists such animals to retain salts. Some aquatic amphibian such as "Xenopus" do not reabsorb water, to prevent excessive water influx. For land-dwelling amphibians, dehydration results in reduced urine output. The amphibian bladder is usually highly distensible and among some land-dwelling species of frogs and salamanders may account for between 20% and 50% of their total body weight. Urine flows from the kidneys through the ureters into the bladder and is periodically released from the bladder to the cloaca. Respiratory system. The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping. Most amphibians, however, are able to exchange gases with the water or air via their skin. To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults.
Reproduction. For the purpose of reproduction, most amphibians require fresh water although some lay their eggs on land and have developed various means of keeping them moist. A few (e.g. "Fejervarya raja") can inhabit brackish water, but there are no true marine amphibians. There are reports, however, of particular amphibian populations unexpectedly invading marine waters. Such was the case with the Black Sea invasion of the natural hybrid "Pelophylax esculentus" reported in 2010. Several hundred frog species in adaptive radiations (e.g., "Eleutherodactylus", the Pacific "Platymantis", the Australo-Papuan microhylids, and many other tropical frogs), however, do not need any water for breeding in the wild. They reproduce via direct development, an ecological and evolutionary adaptation that has allowed them to be completely independent from free-standing water. Almost all of these frogs live in wet tropical rainforests and their eggs hatch directly into miniature versions of the adult, passing through the tadpole stage within the egg. Reproductive success of many amphibians is dependent not only on the quantity of rainfall, but the seasonal timing.
In the tropics, many amphibians breed continuously or at any time of year. In temperate regions, breeding is mostly seasonal, usually in the spring, and is triggered by increasing day length, rising temperatures or rainfall. Experiments have shown the importance of temperature, but the trigger event, especially in arid regions, is often a storm. In anurans, males usually arrive at the breeding sites before females and the vocal chorus they produce may stimulate ovulation in females and the endocrine activity of males that are not yet reproductively active. In caecilians, fertilisation is internal, the male extruding an intromittent organ, the , and inserting it into the female cloaca. The paired Müllerian glands inside the male cloaca secrete a fluid which resembles that produced by mammalian prostate glands and which may transport and nourish the sperm. Fertilisation probably takes place in the oviduct. The majority of salamanders also engage in internal fertilisation. In most of these, the male deposits a spermatophore, a small packet of sperm on top of a gelatinous cone, on the substrate either on land or in the water. The female takes up the sperm packet by grasping it with the lips of the cloaca and pushing it into the vent. The spermatozoa move to the spermatheca in the roof of the cloaca where they remain until ovulation which may be many months later. Courtship rituals and methods of transfer of the spermatophore vary between species. In some, the spermatophore may be placed directly into the female cloaca while in others, the female may be guided to the spermatophore or restrained with an embrace called amplexus. Certain primitive salamanders in the families Sirenidae, Hynobiidae and Cryptobranchidae practice external fertilisation in a similar manner to frogs, with the female laying the eggs in water and the male releasing sperm onto the egg mass.
With a few exceptions, frogs use external fertilisation. The male grasps the female tightly with his forelimbs either behind the arms or in front of the back legs, or in the case of "Epipedobates tricolor", around the neck. They remain in amplexus with their cloacae positioned close together while the female lays the eggs and the male covers them with sperm. Roughened nuptial pads on the male's hands aid in retaining grip. Often the male collects and retains the egg mass, forming a sort of basket with the hind feet. An exception is the granular poison frog ("Oophaga granulifera") where the male and female place their cloacae in close proximity while facing in opposite directions and then release eggs and sperm simultaneously. The tailed frog ("Ascaphus truei") exhibits internal fertilisation. The "tail" is only possessed by the male and is an extension of the cloaca and used to inseminate the female. This frog lives in fast-flowing streams and internal fertilisation prevents the sperm from being washed away before fertilisation occurs. The sperm may be retained in storage tubes attached to the oviduct until the following spring.
Most frogs can be classified as either prolonged or explosive breeders. Typically, prolonged breeders congregate at a breeding site, the males usually arriving first, calling and setting up territories. Other satellite males remain quietly nearby, waiting for their opportunity to take over a territory. The females arrive sporadically, mate selection takes place and eggs are laid. The females depart and territories may change hands. More females appear and in due course, the breeding season comes to an end. Explosive breeders on the other hand are found where temporary pools appear in dry regions after rainfall. These frogs are typically fossorial species that emerge after heavy rains and congregate at a breeding site. They are attracted there by the calling of the first male to find a suitable place, perhaps a pool that forms in the same place each rainy season. The assembled frogs may call in unison and frenzied activity ensues, the males scrambling to mate with the usually smaller number of females. There is a direct competition between males to win the attention of the females in salamanders and newts, with elaborate courtship displays to keep the female's attention long enough to get her interested in choosing him to mate with. Some species store sperm through long breeding seasons, as the extra time may allow for interactions with rival sperm.
Unisexual reproduction. Unisexual female mole salamanders (genus Ambystoma) are common in the Great Lakes region of North America. These salamanders are the oldest known unisexual vertebrate lineage, having emerged about 5 million years ago. Genome exchange can sometimes occur between the unisexual female Ambystoma and males from sympatric sexual species. Life cycle. Most amphibians go through metamorphosis, a process of significant morphological change after birth. In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads and salamanders all hatch from the egg as larvae with external gills. Metamorphosis in amphibians is regulated by thyroxine concentration in the blood, which stimulates metamorphosis, and prolactin, which counteracts thyroxine's effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development is outside the parental body, it is subject to many adaptations due to specific environmental circumstances. For this reason tadpoles can have horny ridges instead of teeth, whisker-like skin extensions or fins. They also make use of a sensory lateral line organ similar to that of fish. After metamorphosis, these organs become redundant and will be reabsorbed by controlled cell death, called apoptosis. The variety of adaptations to specific environmental circumstances among amphibians is wide, with many discoveries still being made.
Eggs. In the egg, the embryo is suspended in perivitelline fluid and surrounded by semi-permeable gelatinous capsules, with the yolk mass providing nutrients. As the larvae hatch, the capsules are dissolved by enzymes secreted from gland at the tip of the snout. The eggs of some salamanders and frogs contain unicellular green algae. These penetrate the jelly envelope after the eggs are laid and may increase the supply of oxygen to the embryo through photosynthesis. They seem to both speed up the development of the larvae and reduce mortality. In the wood frog ("Rana sylvatica"), the interior of the globular egg cluster has been found to be up to warmer than its surroundings, which is an advantage in its cool northern habitat. The eggs may be deposited singly, in cluster or in long strands. Sites for laying eggs include water, mud, burrows, debris and on plants or under logs or stones. The greenhouse frog ("Eleutherodactylus planirostris") lays eggs in small groups in the soil where they develop in about two weeks directly into juvenile frogs without an intervening larval stage. The tungara frog ("Physalaemus pustulosus") builds a floating nest from foam to protect its eggs. First a raft is built, then eggs are laid in the centre, and finally a foam cap is overlaid. The foam has anti-microbial properties. It contains no detergents but is created by whipping up proteins and lectins secreted by the female.
Larvae. The eggs of amphibians are typically laid in water and hatch into free-living larvae that complete their development in water and later transform into either aquatic or terrestrial adults. In many species of frog and in most lungless salamanders (Plethodontidae), direct development takes place, the larvae growing within the eggs and emerging as miniature adults. Many caecilians and some other amphibians lay their eggs on land, and the newly hatched larvae wriggle or are transported to water bodies. Some caecilians, the alpine salamander ("Salamandra atra") and some of the African live-bearing toads ("Nectophrynoides spp.") are viviparous. Their larvae feed on glandular secretions and develop within the female's oviduct, often for long periods. Other amphibians, but not caecilians, are ovoviviparous. The eggs are retained in or on the parent's body, but the larvae subsist on the yolks of their eggs and receive no nourishment from the adult. The larvae emerge at varying stages of their growth, either before or after metamorphosis, according to their species. The toad genus "Nectophrynoides" exhibits all of these developmental patterns among its dozen or so members. Amphibian larvae are known as tadpoles. They have thick, rounded bodies with powerful muscular tails.
Frogs. Unlike in other amphibians, frog tadpoles do not resemble adults. The free-living larvae are normally fully aquatic, but the tadpoles of some species (such as "Nannophrys ceylonensis") are semi-terrestrial and live among wet rocks. Tadpoles have cartilaginous skeletons, gills for respiration (external gills at first, internal gills later), lateral line systems and large tails that they use for swimming. Newly hatched tadpoles soon develop gill pouches that cover the gills. These internal gills and operculum are not homologous with those of fish, and are only found in tadpoles as both salamanders and caecilians have external gills only. Combined with buccal pumping the internal gills has allowed tadpoles to adopt a filter feeding lifestyle, even if several species have since evolved other types of feeding strategies. The lungs develop early and are used as accessory breathing organs, the tadpoles rising to the water surface to gulp air. Some species complete their development inside the egg and hatch directly into small frogs. These larvae do not have gills but instead have specialised areas of skin through which respiration takes place. While tadpoles do not have true teeth, in most species, the jaws have long, parallel rows of small keratinized structures called keradonts surrounded by a horny beak. Front legs are formed under the gill sac and hind legs become visible a few days later.
Iodine and T4 (over stimulate the spectacular apoptosis [programmed cell death] of the cells of the larval gills, tail and fins) also stimulate the evolution of nervous systems transforming the aquatic, vegetarian tadpole into the terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. In fact, tadpoles developing in ponds and streams are typically herbivorous. Pond tadpoles tend to have deep bodies, large caudal fins and small mouths; they swim in the quiet waters feeding on growing or loose fragments of vegetation. Stream dwellers mostly have larger mouths, shallow bodies and caudal fins; they attach themselves to plants and stones and feed on the surface films of algae and bacteria. They also feed on diatoms, filtered from the water through the gills, and stir up the sediment at bottom of the pond, ingesting edible fragments. They have a relatively long, spiral-shaped gut to enable them to digest this diet. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles and fish. Young of the Cuban tree frog ("Osteopilus septentrionalis") can occasionally be cannibalistic, the younger tadpoles attacking a larger, more developed tadpole when it is undergoing metamorphosis.
At metamorphosis, rapid changes in the body take place as the lifestyle of the frog changes completely. The spiral-shaped mouth with horny tooth ridges is reabsorbed together with the spiral gut. The animal develops a large jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, and a tongue is formed. There are associated changes in the neural networks such as development of stereoscopic vision and loss of the lateral line system. All this can happen in about a day. A few days later, the tail is reabsorbed, due to the higher thyroxine concentration required for this to take place. Salamanders. At hatching, a typical salamander larva has eyes without lids, teeth in both upper and lower jaws, three pairs of feathery external gills, and a long tail with dorsal and ventral fins. The forelimbs may be partially developed and the hind limbs are rudimentary in pond-living species but may be rather more developed in species that reproduce in moving water. Pond-type larvae often have a pair of balancers, rod-like structures on either side of the head that may prevent the gills from becoming clogged up with sediment. Both of these are able to breed. Some have larvae that never fully develop into the adult form, a condition known as neoteny. Neoteny occurs when the animal's growth rate is very low and is usually linked to adverse conditions such as low water temperatures that may change the response of the tissues to the hormone thyroxine. as well as lack of food. There are fifteen species of obligate neotenic salamanders, including species of "Necturus", "Proteus" and "Amphiuma", and many examples of facultative ones, such as the northwestern salamander ("Ambystoma gracile") and the tiger salamander ("A. tigrinum") that adopt this strategy under appropriate environmental circumstances.
Lungless salamanders in the family Plethodontidae are terrestrial and lay a small number of unpigmented eggs in a cluster among damp leaf litter. Each egg has a large yolk sac and the larva feeds on this while it develops inside the egg, emerging fully formed as a juvenile salamander. The female salamander often broods the eggs. In the genus "Ensatinas", the female has been observed to coil around them and press her throat area against them, effectively massaging them with a mucous secretion. In newts and salamanders, metamorphosis is less dramatic than in frogs. This is because the larvae are already carnivorous and continue to feed as predators when they are adults so few changes are needed to their digestive systems. Their lungs are functional early, but the larvae do not make as much use of them as do tadpoles. Their gills are never covered by gill sacs and are reabsorbed just before the animals leave the water. Other changes include the reduction in size or loss of tail fins, the closure of gill slits, thickening of the skin, the development of eyelids, and certain changes in dentition and tongue structure. Salamanders are at their most vulnerable at metamorphosis as swimming speeds are reduced and transforming tails are encumbrances on land. Adult salamanders often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin is the required hormone, and for adaptation to the land phase, thyroxine. External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time.
Caecilians. Most terrestrial caecilians that lay eggs do so in burrows or moist places on land near bodies of water. The development of the young of "Ichthyophis glutinosus", a species from Sri Lanka, has been much studied. The eel-like larvae hatch out of the eggs and make their way to water. They have three pairs of external red feathery gills, a blunt head with two rudimentary eyes, a lateral line system and a short tail with fins. They swim by undulating their body from side to side. They are mostly active at night, soon lose their gills and make sorties onto land. Metamorphosis is gradual. By the age of about ten months they have developed a pointed head with sensory tentacles near the mouth and lost their eyes, lateral line systems and tails. The skin thickens, embedded scales develop and the body divides into segments. By this time, the caecilian has constructed a burrow and is living on land. In the majority of species of caecilians, the young are produced by viviparity. "Typhlonectes compressicauda", a species from South America, is typical of these. Up to nine larvae can develop in the oviduct at any one time. They are elongated and have paired sac-like gills, small eyes and specialised scraping teeth. At first, they feed on the yolks of the eggs, but as this source of nourishment declines they begin to rasp at the ciliated epithelial cells that line the oviduct. This stimulates the secretion of fluids rich in lipids and mucoproteins on which they feed along with scrapings from the oviduct wall. They may increase their length sixfold and be two-fifths as long as their mother before being born. By this time they have undergone metamorphosis, lost their eyes and gills, developed a thicker skin and mouth tentacles, and reabsorbed their teeth. A permanent set of teeth grow through soon after birth.
Gills are only necessarily during embryonic development, and in species that give birth the offspring is born after gill degeneration. In egg laying caecilians the gills are either reabsorbed before hatching, or, in species that hatch with gill remnants still present, short lived and only leaves behind a gill slit. For species with scales under their skin, the scales does not form before during metamorphosis. The ringed caecilian ("Siphonops annulatus") has developed a unique adaptation for the purposes of reproduction. The progeny feed on a skin layer that is specially developed by the adult in a phenomenon known as maternal dermatophagy. The brood feed as a batch for about seven minutes at intervals of approximately three days which gives the skin an opportunity to regenerate. Meanwhile, they have been observed to ingest fluid exuded from the maternal cloaca. Parental care. The care of offspring among amphibians has been little studied but, in general, the larger the number of eggs in a batch, the less likely it is that any degree of parental care takes place. Nevertheless, it is estimated that in up to 20% of amphibian species, one or both adults play some role in the care of the young. Those species that breed in smaller water bodies or other specialised habitats tend to have complex patterns of behaviour in the care of their young.
Many woodland salamanders lay clutches of eggs under dead logs or stones on land. The black mountain salamander ("Desmognathus welteri") does this, the mother brooding the eggs and guarding them from predation as the embryos feed on the yolks of their eggs. When fully developed, they break their way out of the egg capsules and disperse as juvenile salamanders. The male hellbender, a primitive salamander, excavates an underwater nest and encourages females to lay there. The male then guards the site for the two or three months before the eggs hatch, using body undulations to fan the eggs and increase their supply of oxygen. The male "Colostethus subpunctatus", a tiny frog, protects the egg cluster which is hidden under a stone or log. When the eggs hatch, the male transports the tadpoles on his back, stuck there by a mucous secretion, to a temporary pool where he dips himself into the water and the tadpoles drop off. The male midwife toad ("Alytes obstetricans") winds egg strings round his thighs and carries the eggs around for up to eight weeks.
The male midwife toad ("Alytes obstetricans") winds egg strings round his thighs and carries the eggs around for up to eight weeks. He keeps them moist and when they are ready to hatch, he visits a pond or ditch and releases the tadpoles. The female gastric-brooding frog ("Rheobatrachus spp.") reared larvae in her stomach after swallowing either the eggs or hatchlings; however, this stage was never observed before the species became extinct. The tadpoles secrete a hormone that inhibits digestion in the mother whilst they develop by consuming their very large yolk supply. The pouched frog ("Assa darlingtoni") lays eggs on the ground. When they hatch, the male carries the tadpoles around in brood pouches on his hind legs. The aquatic Surinam toad ("Pipa pipa") raises its young in pores on its back where they remain until metamorphosis. The granular poison frog ("Oophaga granulifera") is typical of a number of tree frogs in the poison dart frog family Dendrobatidae. Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable water-filled crevice such as the axil of a leaf or the rosette of a bromeliad. Its eggs are laid on the forest floor and when they hatch, the tadpoles are carried one by one on the back of an adult to a suitable water-filled crevice such as the axil of a leaf or the rosette of a bromeliad. The female visits the nursery sites regularly and deposits unfertilised eggs in the water and these are consumed by the tadpoles.
Genetics and genomics. Amphibians are notable among vertebrates for their diversity of chromosomes and genomes. The karyotypes (chromosomes) have been determined for at least 1,193 (14.5%) of the ≈8,200 known (diploid) species, including 963 anurans, 209 salamanders, and 21 caecilians. Generally, the karyotypes of diploid amphibians are characterized by 20–26 bi-armed chromosomes. Amphibians have also very large genomes compared to other taxa of vertebrates and corresponding variation in genome size (C-value: picograms of DNA in haploid nuclei). The genome sizes range from 0.95 to 11.5 pg in frogs, from 13.89 to 120.56 pg in salamanders, and from 2.94 to 11.78 pg in caecilians. The large genome sizes have prevented whole-genome sequencing of amphibians although a number of genomes have been published recently. The 1.7GB draft genome of "Xenopus tropicalis" was the first to be reported for amphibians in 2010. Compared to some salamanders this frog genome is tiny. For instance, the genome of the Mexican axolotl turned out to be 32 Gb, which is more than 10 times larger than the human genome (3GB).
Feeding and diet. With a few exceptions, adult amphibians are predators, feeding on virtually anything that moves that they can swallow. The diet mostly consists of small prey that do not move too fast such as beetles, caterpillars, earthworms and spiders. The sirens ("Siren spp.") often ingest aquatic plant material with the invertebrates on which they feed and a Brazilian tree frog ("Xenohyla truncata") includes a large quantity of fruit in its diet. The Mexican burrowing toad ("Rhinophrynus dorsalis") has a specially adapted tongue for picking up ants and termites. It projects it with the tip foremost whereas other frogs flick out the rear part first, their tongues being hinged at the front. Food is mostly selected by sight, even in conditions of dim light. Movement of the prey triggers a feeding response. Frogs have been caught on fish hooks baited with red flannel and green frogs ("Rana clamitans") have been found with stomachs full of elm seeds that they had seen floating past. Toads, salamanders and caecilians also use smell to detect prey. This response is mostly secondary because salamanders have been observed to remain stationary near odoriferous prey but only feed if it moves. Cave-dwelling amphibians normally hunt by smell. Some salamanders seem to have learned to recognize immobile prey when it has no smell, even in complete darkness.
Amphibians usually swallow food whole but may chew it lightly first to subdue it. They typically have small hinged pedicellate teeth, a feature unique to amphibians. The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals. Salamanders, caecilians and some frogs have one or two rows of teeth in both jaws, but some frogs ("Rana spp.") lack teeth in the lower jaw, and toads ("Bufo spp.") have no teeth. In many amphibians there are also vomerine teeth attached to a facial bone in the roof of the mouth. The tiger salamander ("Ambystoma tigrinum") is typical of the frogs and salamanders that hide under cover ready to ambush unwary invertebrates. Other amphibians, such as the "Bufo spp." toads, actively search for prey, while the Argentine horned frog ("Ceratophrys ornata") lures inquisitive prey closer by raising its hind feet over its back and vibrating its yellow toes. Among leaf litter frogs in Panama, frogs that actively hunt prey have narrow mouths and are slim, often brightly coloured and toxic, while ambushers have wide mouths and are broad and well-camouflaged. Caecilians do not flick their tongues, but catch their prey by grabbing it with their slightly backward-pointing teeth. The struggles of the prey and further jaw movements work it inwards and the caecilian usually retreats into its burrow. The subdued prey is gulped down whole.
When they are newly hatched, frog larvae feed on the yolk of the egg. When this is exhausted some move on to feed on bacteria, algal crusts, detritus and raspings from submerged plants. Water is drawn in through their mouths, which are usually at the bottom of their heads, and passes through branchial food traps between their mouths and their gills where fine particles are trapped in mucus and filtered out. Others have specialised mouthparts consisting of a horny beak edged by several rows of labial teeth. They scrape and bite food of many kinds as well as stirring up the bottom sediment, filtering out larger particles with the papillae around their mouths. Some, such as the spadefoot toads, have strong biting jaws and are carnivorous or even cannibalistic. Vocalization. The calls made by caecilians and salamanders are limited to occasional soft squeaks, grunts or hisses and have not been much studied. A clicking sound sometimes produced by caecilians may be a means of orientation, as in bats, or a form of communication. Most salamanders are considered voiceless, but the California giant salamander ("Dicamptodon ensatus") has vocal cords and can produce a rattling or barking sound. Some species of salamander emit a quiet squeak or yelp if attacked.
Frogs are much more vocal, especially during the breeding season when they use their voices to attract mates. The presence of a particular species in an area may be more easily discerned by its characteristic call than by a fleeting glimpse of the animal itself. In most species, the sound is produced by expelling air from the lungs over the vocal cords into one or more air sacs in the throat or at the corner of the mouth. This may distend like a balloon and acts as a resonator, helping to transfer the sound to the atmosphere, or the water at times when the animal is submerged. The main vocalisation is the male's loud advertisement call which seeks to both encourage a female to approach and discourage other males from intruding on its territory. This call is modified to a quieter courtship call on the approach of a female or to a more aggressive version if a male intruder draws near. Calling carries the risk of attracting predators and involves the expenditure of much energy. Other calls include those given by a female in response to the advertisement call and a release call given by a male or female during unwanted attempts at amplexus. When a frog is attacked, a distress or fright call is emitted, often resembling a scream. The usually nocturnal Cuban tree frog ("Osteopilus septentrionalis") produces a rain call when there is rainfall during daylight hours.
Territorial behaviour. Little is known of the territorial behaviour of caecilians, but some frogs and salamanders defend home ranges. These are usually feeding, breeding or sheltering sites. Males normally exhibit such behaviour though in some species, females and even juveniles are also involved. Although in many frog species, females are larger than males, this is not the case in most species where males are actively involved in territorial defence. Some of these have specific adaptations such as enlarged teeth for biting or spines on the chest, arms or thumbs. In salamanders, defence of a territory involves adopting an aggressive posture and if necessary attacking the intruder. This may involve snapping, chasing and sometimes biting, occasionally causing the loss of a tail. The behaviour of red back salamanders ("Plethodon cinereus") has been much studied. 91% of marked individuals that were later recaptured were within a metre (yard) of their original daytime retreat under a log or rock. A similar proportion, when moved experimentally a distance of , found their way back to their home base. The salamanders left odour marks around their territories which averaged in size and were sometimes inhabited by a male and female pair. These deterred the intrusion of others and delineated the boundaries between neighbouring areas. Much of their behaviour seemed stereotyped and did not involve any actual contact between individuals. An aggressive posture involved raising the body off the ground and glaring at the opponent who often turned away submissively. If the intruder persisted, a biting lunge was usually launched at either the tail region or the naso-labial grooves. Damage to either of these areas can reduce the fitness of the rival, either because of the need to regenerate tissue or because it impairs its ability to detect food.
In frogs, male territorial behaviour is often observed at breeding locations; calling is both an announcement of ownership of part of this resource and an advertisement call to potential mates. In general, a deeper voice represents a heavier and more powerful individual, and this may be sufficient to prevent intrusion by smaller males. Much energy is used in the vocalization and it takes a toll on the territory holder who may be displaced by a fitter rival if he tires. There is a tendency for males to tolerate the holders of neighbouring territories while vigorously attacking unknown intruders. Holders of territories have a "home advantage" and usually come off better in an encounter between two similar-sized frogs. If threats are insufficient, chest to chest tussles may take place. Fighting methods include pushing and shoving, deflating the opponent's vocal sac, seizing him by the head, jumping on his back, biting, chasing, splashing, and ducking him under the water. Defence mechanisms.
In locations where both snake and salamander co-exist, the snakes have developed immunity through genetic changes and they feed on the amphibians with impunity. Coevolution occurs with the newt increasing its toxic capabilities at the same rate as the snake further develops its immunity. Some frogs and toads are toxic, the main poison glands being at the side of the neck and under the warts on the back. These regions are presented to the attacking animal and their secretions may be foul-tasting or cause various physical or neurological symptoms. Altogether, over 200 toxins have been isolated from the limited number of amphibian species that have been investigated. Poisonous species often use bright colouring to warn potential predators of their toxicity. These warning colours tend to be red or yellow combined with black, with the fire salamander ("Salamandra salamandra") being an example. Once a predator has sampled one of these, it is likely to remember the colouration next time it encounters a similar animal. In some species, such as the fire-bellied toad ("Bombina spp."), the warning colouration is on the belly and these animals adopt a defensive pose when attacked, exhibiting their bright colours to the predator. The frog "Allobates zaparo" is not poisonous, but mimics the appearance of other toxic species in its locality, a strategy that may deceive predators.
Many amphibians are nocturnal and hide during the day, thereby avoiding diurnal predators that hunt by sight. Other amphibians use camouflage to avoid being detected. They have various colourings such as mottled browns, greys and olives to blend into the background. Some salamanders adopt defensive poses when faced by a potential predator such as the North American northern short-tailed shrew ("Blarina brevicauda"). Their bodies writhe and they raise and lash their tails which makes it difficult for the predator to avoid contact with their poison-producing granular glands. A few salamanders will autotomise their tails when attacked, sacrificing this part of their anatomy to enable them to escape. The tail may have a constriction at its base to allow it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads ("Pelobates spp") scream and leap towards the attacker. Giant salamanders of the genus "Andrias", as well as Ceratophrine and "Pyxicephalus" frogs possess sharp teeth and are capable of drawing blood with a defensive bite. The blackbelly salamander ("Desmognathus quadramaculatus") can bite an attacking common garter snake ("Thamnophis sirtalis") two or three times its size on the head and often manages to escape.
Cognition. In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. Amphibians are widely considered to be sentient, able to feel emotions such as anxiety and fear. In one experiment, when offered live fruit flies ("Drosophila virilis"), salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish between low numbers (1 vs 2, 2 vs 3, but not 3 vs 4) and large numbers (3 vs 6, 4 vs 8, but not 4 vs 6) of prey. This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area. Conservation. Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction rates—possibly 1,024 times higher. In 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Of these, 1,356 (33.6%) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, global warming, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like chytridiomycosis. However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion.
Food webs and predation. Any decline in amphibian numbers will affect the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake ("Thamnophis elegans") in California is largely aquatic and depends heavily on two species of frog that are decreasing in numbers, the Yosemite toad ("Bufo canorus") and the mountain yellow-legged frog ("Rana muscosa"), putting the snake's future at risk. If the snake were to become scarce, this would affect birds of prey and other predators that feed on it. Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences.
Pollution and pesticides. The decline in amphibian and reptile populations has led to an awareness of the effects of pesticides on reptiles and amphibians. In the past, the argument that amphibians or reptiles were more susceptible to any chemical contamination than any land aquatic vertebrate was not supported by research until recently. Amphibians and reptiles have complex life cycles, live in different climate and ecological zones, and are more vulnerable to chemical exposure. Certain pesticides, such as organophosphates, neonicotinoids, and carbamates, react via cholinesterase inhibition. Cholinesterase is an enzyme that causes the hydrolysis of acetylcholine, an excitatory neurotransmitter that is abundant in the nervous system. AChE inhibitors are either reversible or irreversible, and carbamates are safer than organophosphorus insecticides, which are more likely to cause cholinergic poisoning. Reptile exposure to an AChE inhibitory pesticide may result in disruption of neural function in reptiles. The buildup of these inhibitory effects on motor performance, such as food consumption and other activities.
Conservation and protection strategies. The Amphibian Specialist Group of the IUCN is spearheading efforts to implement a comprehensive global strategy for amphibian conservation. Amphibian Ark is an organization that was formed to implement the ex-situ conservation recommendations of this plan, and they have been working with zoos and aquaria around the world, encouraging them to create assurance colonies of threatened amphibians. One such project is the Panama Amphibian Rescue and Conservation Project that built on existing conservation efforts in Panama to create a country-wide response to the threat of chytridiomycosis. Another measure would be to stop exploitation of frogs for human consumption. In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was already linked to an increase in mosquitoes and thus has direct consequences for human health.
Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the northernmost, westernmost, and easternmost (the Aleutian Islands cross the 180th meridian into the eastern hemisphere) state in the United States. It borders the Canadian territory of Yukon and the province of British Columbia to the east. It shares a western maritime border, in the Bering Strait, with Russia's Chukotka Autonomous Okrug. The Chukchi and Beaufort Seas of the Arctic Ocean lie to the north, and the Pacific Ocean lies to the south. Technically, it is a semi-exclave of the U.S., and is the largest exclave in the world. Alaska is the largest U.S. state by area, comprising more total area than the following three largest states of Texas, California, and Montana combined, and is the seventh-largest subnational division in the world. It is the third-least populous and most sparsely populated U.S. state; however, with a population of 740,133 as of 2024, it is the most populous territory in North America located mostly north of the 60th parallel, with more than quadruple the combined populations of Northern Canada and Greenland. The state contains the four largest cities in the United States by area, including the state capital of Juneau. The state's most populous city is Anchorage, and approximately half of Alaska's residents live within its metropolitan area.
Indigenous people have lived in Alaska for thousands of years, and it is widely believed that the region served as the entry point for the initial settlement of North America by way of the Bering land bridge. The Russian Empire was the first to actively colonize the area beginning in the 18th century, eventually establishing Russian America, which spanned most of the current state and promoted and maintained a native Alaskan Creole population. The expense and logistical difficulty of maintaining this distant possession prompted its sale to the U.S. in 1867 for US$7.2 million (equivalent to $ million in ). The area went through several administrative changes before becoming organized as a territory on May 11, 1912. It was admitted as the 49th state of the U.S. on January 3, 1959. Abundant natural resources have enabled Alaska— with one of the smallest state economies—to have one of the highest per capita incomes, with commercial fishing, and the extraction of natural gas and oil, dominating Alaska's economy. U.S. Armed Forces bases and tourism also contribute to the economy; more than half of the state is federally-owned land containing national forests, national parks, and wildlife refuges. It is among the most irreligious states and one of the first to legalize recreational marijuana. The Indigenous population of Alaska is proportionally the second highest of any U.S. state, at over 15 percent, after only Hawaii.
Etymology. The name "Alaska" () was introduced during the Russian colonial period when it was used to refer to the Alaska Peninsula. It was derived from an Aleut-language idiom, , meaning "the mainland" or, more literally, "the object towards which the action of the sea is directed". History. Pre-colonization. Numerous indigenous peoples occupied Alaska for thousands of years before the arrival of European peoples to the area. Linguistic and DNA studies done here have provided evidence for the settlement of North America by way of the Bering land bridge. At the Upward Sun River site in the Tanana Valley in Alaska, remains of a six-week-old infant were found. The baby's DNA showed that she belonged to a population that was genetically separate from other native groups present elsewhere in the New World at the end of the Pleistocene. Ben Potter, the University of Alaska Fairbanks archaeologist who unearthed the remains at the Upward Sun River site in 2013, named this new group Ancient Beringian. The Tlingit people developed a society with a matrilineal kinship system of property inheritance and descent in what is today Southeast Alaska, along with parts of British Columbia and the Yukon. Also in Southeast were the Haida, now well known for their unique arts. The Tsimshian people came to Alaska from British Columbia in 1887, when President Grover Cleveland, and later the U.S. Congress, granted them permission to settle on Annette Island and found the town of Metlakatla, Alaska. All three of these peoples, as well as other indigenous peoples of the Pacific Northwest Coast, experienced smallpox outbreaks from the late 18th through the mid-19th century, with the most devastating epidemics occurring in the 1830s and 1860s, resulting in high fatalities and social disruption.
Colonization. Some researchers believe the first Russian settlement in Alaska was established in the 17th century. According to this hypothesis, in 1648 several koches of Semyon Dezhnyov's expedition came ashore in Alaska by storm and founded this settlement. This hypothesis is based on the testimony of Chukchi geographer Nikolai Daurkin, who had visited Alaska in 1764–1765 and who had reported on a village on the Kheuveren River, populated by "bearded men" who "pray to the icons". Some modern researchers associate Kheuveren with Koyuk River. The first European vessel to reach Alaska is generally held to be the "St. Gabriel" under the authority of the surveyor M. S. Gvozdev and assistant navigator I. Fyodorov on August 21, 1732, during an expedition of Siberian Cossack A. F. Shestakov and Russian explorer Dmitry Pavlutsky (1729–1735). Another European contact with Alaska occurred in 1741, when Vitus Bering led an expedition for the Russian Navy aboard the "St. Peter". After his crew returned to Russia with sea otter pelts judged to be the finest fur in the world, small associations of fur traders began to sail from the shores of Siberia toward the Aleutian Islands. The first permanent European settlement was founded in 1784.
Between 1774 and 1800, Spain sent several expeditions to Alaska to assert its claim over the Pacific Northwest. In 1789, a Spanish settlement and fort were built in Nootka Sound. These expeditions gave names to places such as Valdez, Bucareli Sound, and Cordova. Later, the Russian-American Company carried out an expanded colonization program during the early-to-mid-19th century. Sitka, renamed New Archangel from 1804 to 1867, on Baranof Island in the Alexander Archipelago in what is now Southeast Alaska, became the capital of Russian America. It remained the capital after the colony was transferred to the United States. The Russians never fully colonized Alaska, and the colony was never very profitable. Evidence of Russian settlement in names and churches survives throughout southeastern Alaska. In 1867, William H. Seward, the United States Secretary of State under President Andrew Johnson, negotiated the Alaska Purchase (referred to pejoratively as Seward's Folly) with the Russians for $7.2 million. Russia's contemporary ruler Tsar Alexander II, the Emperor of the Russian Empire, King of Poland and Grand Duke of Finland, also planned the sale; the purchase was made on March 30, 1867. Six months later the commissioners arrived in Sitka and the formal transfer was arranged; the formal flag-raising took place at Fort Sitka on October 18, 1867. In the ceremony, 250 uniformed U.S. soldiers marched to the governor's house at "Castle Hill", where the Russian troops lowered the Russian flag and the U.S. flag was raised. This event is celebrated as Alaska Day, a legal holiday on October 18.
Alaska was loosely governed by the military initially and was administered as a district starting in 1884, with a governor appointed by the United States president. A federal district court was headquartered in Sitka. For most of Alaska's first decade under the United States flag, Sitka was the only community inhabited by American settlers. They organized a "provisional city government", which was Alaska's first municipal government, but not in a legal sense. Legislation allowing Alaskan communities to legally incorporate as cities did not come about until 1900, and home rule for cities was extremely limited or unavailable until statehood took effect in 1959. U.S. territorial incorporation. Starting in the 1890s and stretching in some places to the early 1910s, gold rushes in Alaska and the nearby Yukon Territory brought thousands of miners and settlers to Alaska. From 1879 to 1920, Alaska produced a cumulative total of over $460,000,000 () of mineral production. Alaska was officially incorporated as an organized territory in 1912. Alaska's capital, which had been in Sitka until 1906, was moved north to Juneau. Construction of the Alaska Governor's Mansion began that same year. European immigrants from Norway and Sweden also settled in southeast Alaska, where they entered the fishing and logging industries.
During World War II, the Aleutian Islands Campaign focused on Attu, Agattu and Kiska, all of which were occupied by the Empire of Japan. During the Japanese occupation, an American civilian and two United States Navy personnel were killed at Attu and Kiska respectively, and nearly a total of 50 Aleut civilians and eight sailors were interned in Japan. About half of the Aleuts died during the period of internment. Unalaska/Dutch Harbor and Adak became significant bases for the United States Army, United States Army Air Forces and United States Navy. The United States Lend-Lease program involved flying American warplanes through Canada to Fairbanks and then Nome; Soviet pilots took possession of these aircraft, ferrying them to fight the German invasion of the Soviet Union. The construction of military bases contributed to the population growth of some Alaskan cities. Statehood. Statehood for Alaska was an important cause of James Wickersham early in his tenure as a congressional delegate. Decades later, the statehood movement gained its first real momentum following a territorial referendum in 1946. The Alaska Statehood Committee and Alaska's Constitutional Convention would soon follow. Statehood supporters also found themselves fighting major battles against political foes, mostly in the U.S. Congress but also within Alaska. Statehood was approved by the U.S. Congress on July 7, 1958; Alaska was officially proclaimed a state on January 3, 1959.
Good Friday earthquake. On March 27, 1964, the massive Good Friday earthquake killed 133 people and destroyed several villages and portions of large coastal communities, mainly by the resultant tsunamis and landslides. It was the fourth-most-powerful earthquake in recorded history, with a moment magnitude of 9.2 (more than a thousand times as powerful as the 1989 San Francisco earthquake). The time of day (5:36 pm), time of year (spring) and location of the epicenter were all cited as factors in potentially sparing thousands of lives, particularly in Anchorage. Alaska suffered a more severe megathrust earthquake on July 11, 1585, estimated at magnitude 9.25, which remains the most powerful earthquake recorded in North American history, and the second most powerful earthquake recorded in world history. The Good Friday earthquake lasted 4 minutes and 38 seconds. of fault ruptured at once and moved up to , releasing about 500 years of stress buildup. Soil liquefaction, fissures, landslides, and other ground failures caused major structural damage in several communities and much damage to property. Anchorage sustained great destruction or damage to many inadequately earthquake-engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other human-made equipment), particularly in the several landslide zones along Knik Arm. southwest, some areas near Kodiak were permanently raised by . Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as , requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.
In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 32 people between the collapse of the Valdez city harbor and docks, and inside the ship that was docked there at the time. Nearby, a tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there; survivors out-ran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Washington, Oregon, and California. Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was also reported from Florida and Texas. Alaska had never experienced a major disaster in a highly populated area before and had very limited resources for dealing with the effects of such an event. In Anchorage, at the urging of geologist Lidia Selkregg, the City of Anchorage and the Alaska State Housing Authority appointed a team of 40 scientists, including geologists, soil scientists, and engineers, to assess the damage done by the earthquake to the city. The team, called the Engineering and Geological Evaluation Group, was headed by Ruth A. M. Schmidt, a geology professor at the University of Alaska Anchorage. The team of scientists came into conflict with local developers and downtown business owners who wanted to immediately rebuild; the scientists wanted to identify future dangers to ensure that the rebuilt infrastructure would be safe. The team produced a report on May 8, 1964, just a little more than a month after the earthquake.
The United States military, which has a large active presence in Alaska, also stepped in to assist within moments of the end of the quake. The U.S. Army rapidly re-established communications with the lower 48 states, deployed troops to assist the citizens of Anchorage, and dispatched a convoy to Valdez. On the advice of military and civilian leaders, President Lyndon B. Johnson declared all of Alaska a major disaster area the day after the quake. The U.S. Navy and U.S. Coast Guard deployed ships to isolated coastal communities to assist with immediate needs. Bad weather and poor visibility hampered air rescue and observation efforts the day after the quake, but on Sunday the 29th the situation improved and rescue helicopters and observation aircraft were deployed. A military airlift immediately began shipping relief supplies to Alaska, eventually delivering of food and other supplies. Broadcast journalist, Genie Chance, assisted in recovery and relief efforts, staying on the KENI air waves over Anchorage for more than 24 continuous hours as the voice of calm from her temporary post within the Anchorage Public Safety Building. She was effectively designated as the public safety officer by the city's police chief. Chance provided breaking news of the catastrophic events that continued to develop following the magnitude 9.2 earthquake, and she served as the voice of the public safety office, coordinating response efforts, connecting available resources to needs around the community, disseminating information about shelters and prepared food rations, passing messages of well-being between loved ones, and helping to reunite families.
In the longer term, the U.S. Army Corps of Engineers led the effort to rebuild roads, clear debris, and establish new townsites for communities that had been completely destroyed, at a cost of $110 million. The West Coast and Alaska Tsunami Warning Center was formed as a direct response to the disaster. Federal disaster relief funds paid for reconstruction as well as financially supporting the devastated infrastructure of Alaska's government, spending hundreds of millions of dollars that helped keep Alaska financially solvent until the discovery of massive oil deposits at Prudhoe Bay. At the order of the U.S. Defense Department, the Alaska National Guard founded the Alaska Division of Emergency Services to respond to any future disasters. Oil boom. The 1968 discovery of oil at Prudhoe Bay and the 1977 completion of the Trans-Alaska Pipeline System led to an oil boom. Royalty revenues from oil have funded large state budgets from 1980 onward. Oil production was not the only economic value of Alaska's land. In the second half of the 20th century, Alaska discovered tourism as an important source of revenue. Tourism became popular after World War II when military personnel stationed in the region returned home praising its natural splendor. The Alcan Highway, built during the war, and the Alaska Marine Highway System, completed in 1963, made the state more accessible than before. Tourism has become increasingly important in Alaska, and today over 1.4 million people visit the state each year.
With tourism more vital to the economy, environmentalism also rose in importance. The Alaska National Interest Lands Conservation Act (ANILCA) of 1980 added 53.7 million acres (217,000 km2) to the National Wildlife Refuge system, parts of 25 rivers to the National Wild and Scenic Rivers System, 3.3 million acres (13,000 km2) to National Forest lands, and 43.6 million acres (176,000 km2) to National Park land. Because of the Act, Alaska now contains two-thirds of all American national parklands. Today, more than half of Alaskan land is owned by the Federal Government. In 1989, the "Exxon Valdez" hit a reef in the Prince William Sound, spilling more than 11 million gallons (42 megalitres) of crude oil over of coastline. Today, the battle between philosophies of development and conservation is seen in the contentious debate over oil drilling in the Arctic National Wildlife Refuge and the proposed Pebble Mine. Geography. Located at the northwest corner of North America, Alaska is the northernmost and westernmost state in the United States, but also has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U.S. state on continental North America; about of Canadian territory consisting of British Columbia (in Canada) separates Alaska from Washington. It is technically part of the continental U.S., but is not usually included in the colloquial use of the term; Alaska is not part of the contiguous U.S., often called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. The largest lake in Alaska is Lake Illiamna.
The state is bordered by Canada's Yukon and British Columbia to the east (making it the only state to border only a Canadian territory); the Gulf of Alaska and the Pacific Ocean to the south and southwest; the Bering Sea, Bering Strait, and Chukchi Sea to the west; and the Arctic Ocean to the north. Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only apart. Alaska has a longer coastline than all the other U.S. states combined. At in total area, Alaska is by far the largest state in the United States. Alaska is more than twice the size of the second-largest U.S. state (Texas), and it is larger than the next three largest states (Texas, California, and Montana) combined. Alaska is the seventh largest subnational division in the world. If it was an independent nation, it would be the 18th largest country in the world; almost the same size as Iran. With its myriad islands, Alaska has nearly of tidal shoreline. The Aleutian Islands chain extends west from the southern tip of the Alaska Peninsula. Many active volcanoes are found in the Aleutians and in coastal regions. Unimak Island, for example, is home to Mount Shishaldin, which is an occasionally smoldering volcano that rises to above the North Pacific. The chain of volcanoes extends to Mount Spurr, west of Anchorage on the mainland. Geologists have identified Alaska as part of Wrangellia, a large region consisting of multiple states and Canadian provinces in the Pacific Northwest, which is actively undergoing continent building.
One of the world's largest tides occurs in Turnagain Arm, just south of Anchorage, where tidal differences can be more than . Alaska has more than 409,000 natural lakes at least one hectare or bigger. Marshlands and wetland permafrost cover (mostly in northern, western and southwest flatlands). Glacier ice covers about of Alaska. The Bering Glacier is the largest glacier in North America, covering alone. Regions. There are no officially defined borders demarcating the various regions of Alaska, however there are five/six regions that the state is most commonly broken up into: Southcentral. The most populous region of Alaska contains Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula. Rural, mostly unpopulated areas south of the Alaska Range and west of the Wrangell Mountains also fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez. Southeast. Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the contiguous states. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaska's largest city. The Alaska Marine Highway provides a vital surface transportation link throughout the area and country, as only three communities (Haines, Hyder and Skagway) enjoy direct connections to the contiguous North American road system.
Interior. The Interior is the largest region of Alaska; much of it is uninhabited wilderness. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali, federally designated as Mount McKinley, is the highest mountain in North America and is also located here. North Slope. The North Slope is mostly tundra peppered with small villages. The area is known for its massive reserves of crude oil and contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field. The city of Utqiaġvik, formerly known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and also containing the Kobuk River valley, is often considered part of this region. The respective Inupiat of the North Slope and of the Northwest Arctic seldom consider themselves to be one people. Southwest. Southwest Alaska is a sparsely inhabited region stretching some inland from the Bering Sea. Most of the population lives along the coast. Kodiak Island is also located in the Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of the Southwest, with the Aleutian Islands often (but not always) being grouped in as well.
Aleutian Islands. While primarily part of Southwest Alaska when grouped economically, the Aleutian islands are sometimes recognized as an alternate group from the rest of the region due to the geographic separation from the continent. More than 300 small volcanic islands make up this chain, which stretches more than into the Pacific Ocean. Some of these islands fall in the Eastern Hemisphere, but the International Date Line was drawn west of 180° to keep the whole state, and thus the entire North American continent, within the same legal day. Two of the islands, Attu and Kiska, were occupied by Japanese forces during World War II. Land ownership. As of 2023, the United States Bureau of Land Management mangages 290 million of surface and subsurface acres as public lands, including a multitude of national forests, national parks, national wildlife refuges, and federal mineral estate land. Of these, the Bureau of Land Management manages , or 23.8% of the state. The Arctic National Wildlife Refuge is managed by the United States Fish and Wildlife Service. It is the world's largest wildlife refuge, comprising .
Of the remaining land area, the state of Alaska owns , its entitlement under the Alaska Statehood Act. A portion of that acreage is occasionally ceded to the organized boroughs presented above, under the statutory provisions pertaining to newly formed boroughs. Smaller portions are set aside for rural subdivisions and other homesteading-related opportunities. These are not very popular due to the often remote and roadless locations. The University of Alaska, as a land grant university, also owns substantial acreage which it manages independently. Another are owned by 12 regional, and scores of local, Native corporations created under the Alaska Native Claims Settlement Act (ANCSA) of 1971. Regional Native corporation Doyon, Limited often promotes itself as the largest private landowner in Alaska in advertisements and other communications. Provisions of ANCSA allowing the corporations' land holdings to be sold on the open market starting in 1991 were repealed before they could take effect. Effectively, the corporations hold title (including subsurface title in many cases, a privilege denied to individual Alaskans) but cannot sell the land. Individual Native allotments are sold on the open market.
Various private interests own the remaining land, totaling about one percent of the state. Alaska is, by a large margin, the state with the smallest percentage of private land ownership when Native corporation holdings are excluded. Alaska Heritage Resources Survey. The Alaska Heritage Resources Survey (AHRS) is a restricted inventory of all reported historic and prehistoric sites within the U.S. state of Alaska; it is maintained by the Office of History and Archaeology. The survey's inventory of cultural resources includes objects, structures, buildings, sites, districts, and travel ways, with a general provision that they are more than fifty years old. , more than 35,000 sites have been reported. Cities, towns and boroughs. Alaska is not divided into counties, like Louisiana's parishes and unlike most of the other U.S. states, but it is divided into "boroughs". Delegates to the Alaska Constitutional Convention wanted to avoid the pitfalls of the traditional county system and adopted their own unique model. Many of the more densely populated parts of the state are part of Alaska's 16 boroughs, which function somewhat similarly to counties in other states. Unlike county-equivalents in the other states, the boroughs do not cover the state's entire land area. The area not part of any borough is referred to as the Unorganized Borough.
The Unorganized Borough has no government of its own, but the U.S. Census Bureau in cooperation with the state divided the Unorganized Borough into 11 census areas solely for the purposes of statistical analysis and presentation. A "recording district" is a mechanism for management of the public record in Alaska. The state is divided into 34 recording districts which are centrally administered under a state recorder. All recording districts use the same acceptance criteria, fee schedule, etc., for accepting documents into the public record. Whereas many U.S. states use a three-tiered system of decentralization—state/county/township—most of Alaska uses only two tiers—state/borough. Owing to the low population density, most of the land is located in the Unorganized Borough. As the name implies, it has no intermediate borough government but is administered directly by the state government. In 2000, 57.71% of Alaska's area has this status, with 13.05% of the population. Anchorage merged the city government with the Greater Anchorage Area Borough in 1975 to form the Municipality of Anchorage, containing the city proper and the communities of Eagle River, Chugiak, Peters Creek, Girdwood, Bird, and Indian. Fairbanks has a separate borough (the Fairbanks North Star Borough) and municipality (the City of Fairbanks).
The state's most populous city is Anchorage, home to 291,247 people in 2020. The richest location in Alaska by per capita income is Denali ($42,245). Yakutat City, Sitka, Juneau, and Anchorage are the four largest cities in the U.S. by area. Cities and census-designated places (by population). As reflected in the 2020 United States census, Alaska has a total of 355 incorporated cities and census-designated places (CDPs). The tally of cities includes four unified municipalities, essentially the equivalent of a consolidated city–county. The majority of these communities are located in the rural expanse of Alaska known as "The Bush" and are unconnected to that contiguous North American road network. The table at the bottom of this section lists the 100 largest cities and census-designated places in Alaska, in population order. Of Alaska's 2020 U.S. census population figure of 733,391, 16,655 people, or 2.27% of the population, did not live in an incorporated city or census-designated place. Approximately three-quarters of that figure were people who live in urban and suburban neighborhoods on the outskirts of the city limits of Ketchikan, Kodiak, Palmer and Wasilla. CDPs have not been established for these areas by the United States Census Bureau, except that seven CDPs were established for the Ketchikan-area neighborhoods in the 1980 census (Clover Pass, Herring Cove, Ketchikan East, Mountain Point, Alaska Route 7, Pennock Island and Saxman East), but have not been used since. The remaining population was scattered throughout Alaska, both within organized boroughs and in the Unorganized Borough, in largely remote areas.
Climate. Alaska is the coldest state in the United States. The climate in the south and southeastern Alaska is a mid-latitude oceanic climate (Köppen climate classification: "Cfb"), and a subarctic oceanic climate (Köppen "Cfc") in the northern parts, with cool summers and relatively mild winters. On an annual basis, the southeast is both the wettest and warmest part of Alaska with milder temperatures in the winter and high precipitation throughout the year. Juneau averages over of precipitation a year, and Ketchikan averages over . This is also the only region in Alaska in which the average daytime high temperature is above freezing during the winter months.The climate of Anchorage and south central Alaska is mild by Alaskan standards due to the region's proximity to the seacoast. While the area gets less rain than southeast Alaska, it gets more snow, and days tend to be clearer. On average, Anchorage receives of precipitation a year, with around of snow, although there are areas in the south central which receive far more snow. It is a subarctic climate () due to its brief, cool summers.
The climate of western Alaska is determined in large part by the Bering Sea and the Gulf of Alaska. It is a subarctic oceanic climate in the southwest and a continental subarctic climate farther north. The temperature is somewhat moderate considering how far north the area is. This region has a tremendous amount of variety in precipitation. An area stretching from the northern side of the Seward Peninsula to the Kobuk River valley (i.e., the region around Kotzebue Sound) is technically a desert, with portions receiving less than of precipitation annually. On the other extreme, some locations between Dillingham and Bethel average around of precipitation. The climate of the interior of Alaska is subarctic and is a classic example of a continental subarctic climate, except in a few valleys where the climate approaches humid continental (Köppen: "Dfb"). Some of the highest and lowest temperatures in Alaska occur around the area near Fairbanks. Summers are warm (albeit generally short) and may have temperatures reaching into the 90s °F (the low-to-mid 30s °C), while in the long and very cold winters, the temperature can fall below . Precipitation is sparse in the Interior, often less than a year, but what precipitation falls in the winter tends to stay the entire winter.
The highest and lowest recorded temperatures in Alaska are both in the Interior. The highest is in Fort Yukon (which is just inside the arctic circle) on June 27, 1915, making Alaska tied with Hawaii as the state with the lowest high temperature in the United States. The lowest official Alaska temperature is in Prospect Creek on January 23, 1971, one degree above the lowest temperature recorded in continental North America (in Snag, Yukon, Canada). The climate in the extreme north of Alaska, north of the Brooks Range, is Arctic () with long, very cold winters and short, cool summers. Even in July, the average low temperature in Utqiaġvik is . Precipitation is light in this part of Alaska, with many places averaging less than per year, mostly as snow which stays on the ground almost the entire year. Demographics. The United States Census Bureau found in the 2020 United States census that the population of Alaska was 733,391 on April 1, 2020, a 3.3% increase since the 2010 United States census. According to the 2010 United States Census, the U.S. state of Alaska had a population of 710,231, a 13.3% increase from 626,932 at the 2000 U.S. census.
In 2020, Alaska ranked as the 48th largest state by population, ahead of only Vermont and Wyoming. Alaska is the least densely populated state, and one of the most sparsely populated areas in the world, at , with the next state, Wyoming, at . Alaska is by far the largest U.S. state by area, and the tenth wealthiest (per capita income). due to its population size, it is one of 14 U.S. states that still have only one telephone area code. According to HUD's 2022 Annual Homeless Assessment Report, there were an estimated 2,320 homeless people in Alaska. Race and ethnicity. The 2019 American Community Survey estimated 60.2% of the population was non-Hispanic white, 3.7% black or African American, 15.6% American Indian or Alaska Native, 6.5% Asian, 1.4% Native Hawaiian and other Pacific Islander, 7.5% two or more races, and 7.3% Hispanic or Latin American of any race. At the survey estimates, 7.8% of the total population was foreign-born from 2015 to 2019. In 2015, 61.3% was non-Hispanic white, 3.4% black or African American, 13.3% American Indian or Alaska Native, 6.2% Asian, 0.9% Native Hawaiian and other Pacific Islander, 0.3% some other race, and 7.7% multiracial. Hispanics and Latin Americans were 7% of the state population in 2015. From 2015 to 2019, the largest Hispanic and Latin American groups were Mexican Americans, Puerto Ricans, and Cuban Americans. The largest Asian groups living in the state were Filipinos, Korean Americans, and Japanese and Chinese Americans.
The state was 66.7% white (64.1% non-Hispanic white), 14.8% American Indian and Alaska Native, 5.4% Asian, 3.3% black or African American, 1.0% Native Hawaiian and other Pacific Islander, 1.6% from some other race, and 7.3% from two or more races in 2010. Hispanics or Latin Americans of any race made up 5.5% of the population in 2010. , 50.7% of Alaska's population younger than one year of age belonged to minority groups (i.e., did not have two parents of non-Hispanic white ancestry). In 1960, the United States Census Bureau reported Alaska's population as 77.2% white, 3% black, and 18.8% American Indian and Alaska Native. In 2018, the top countries of origin for Alaska's immigrants were the Philippines, Mexico, Canada, Thailand and South Korea. Languages. According to the 2011 American Community Survey, 83.4% of people over the age of five spoke only English at home. About 3.5% spoke Spanish at home, 2.2% spoke another Indo-European language, about 4.3% spoke an Asian language (including Tagalog), and about 5.3% spoke other languages at home. In 2019, the American Community Survey determined 83.7% spoke only English, and 16.3% spoke another language other than English. The most spoken European language after English was Spanish, spoken by approximately 4.0% of the state population. Collectively, Asian and Pacific Islander languages were spoken by 5.6% of Alaskans. Since 2010, a total of 5.2% of Alaskans speak one of the state's 20 indigenous languages, known locally as "native languages".
The Alaska Native Language Center at the University of Alaska Fairbanks claims that at least 20 Alaskan native languages exist and there are also some languages with different dialects. Most of Alaska's native languages belong to either the Eskimo–Aleut or Na-Dene language families; some languages are thought to be isolates (e.g. Haida) or have not yet been classified (e.g. Tsimshianic). nearly all of Alaska's native languages were classified as either threatened, shifting, moribund, nearly extinct, or dormant languages. In October 2014, the governor of Alaska signed a bill declaring the state's 20 indigenous languages to have official status. This bill gave them symbolic recognition as official languages, though they have not been adopted for official use within the government. The 20 languages that were included in the bill are: Religion. Multiple surveys have ranked Alaska among the most irreligious states. According to statistics collected by the Association of Religion Data Archives (ARDA) from 2010, about 34% of Alaska residents were members of religious congregations. Of the religious population, roughly 4% were Mormon, 0.5% Jewish, 0.5% Muslim, 1% Buddhist, 0.2% Baháʼí, and 0.5% Hindu. The largest religious denominations in Alaska was the Catholic Church with 50,866 adherents; non-denominational Evangelicals with 38,070 adherents; The Church of Jesus Christ of Latter-day Saints with 32,170 adherents; and the Southern Baptist Convention with 19,891 adherents. Alaska has been identified, along with Washington and Oregon in the Pacific Northwest, as being the least religious states in the United States, in terms of church membership.
The Pew Research Center in 2014 determined 62% of the adult population practiced Christianity. Of the Christian denominations, Catholicism was the largest Christian group. When Protestant denominations were combined, Protestantism was the largest Christian tradition, with Evangelicalism being the largest movement within the Protestant group. The unaffiliated population made up the largest non-Christian religious affiliation at 37%. Atheists made up 5% of the population and the largest non-Christian religion was Buddhism. In 2020, the Public Religion Research Institute (PRRI) determined 57% of adults were Christian. By 2022, Christianity increased to 77% of the population according to the PRRI. Through the Association of Religion Data Archives in 2020, its Christian population was dominated by non/inter-denominational Protestantism as the single largest Christian cohort, with 73,930 adherents. Roman Catholics were second with 40,280 members; throughout its Christian population, non-denominational Christians had an adherence rate of 100.81 per 1,000 residents, and Catholics 54.92 per 1,000 residents. Per 2014's Pew study, religion was seen as very important to 41% of the population, although 29% considered it somewhat important. In 2014, Pew determined roughly 55% believed in God with absolute certainty, and 24% believed fairly certainly. Reflecting the separate 2020 ARDA study, the 2014 Pew study showed 30% attended religious services once a week, 34% once or twice a month, and 36% seldom/never. In 2018, "The Gospel Coalition" published an article using Pew data and determined non-churchgoing Christians nationwide did not attend religious services often through the following: practicing the faith in other ways, not finding a house of worship they liked, disliking sermons and feeling unwelcomed, and logistics.
In 1795, the first Russian Orthodox Church was established in Kodiak. Intermarriage with Alaskan Natives helped the Russian immigrants integrate into society. As a result, an increasing number of Russian Orthodox churches gradually became established within Alaska. Alaska also has the largest Quaker population (by percentage) of any state. In 2009, there were 6,000 Jews in Alaska (for whom observance of halakha may pose special problems). Alaskan Hindus often share venues and celebrations with members of other Asian religious communities, including Sikhs and Jains. In 2010, Alaskan Hindus established the Sri Ganesha Temple of Alaska, making it the first Hindu Temple in Alaska and the northernmost Hindu Temple in the world. There are an estimated 2,000–3,000 Hindus in Alaska. The vast majority of Hindus live in Anchorage or Fairbanks. Estimates for the number of Muslims in Alaska range from 2,000 to 5,000. In 2020, ARDA estimated there were 400 Muslims in the state. The Islamic Community Center of Anchorage began efforts in the late 1990s to construct a mosque in Anchorage. They broke ground on a building in south Anchorage in 2010 and were nearing completion in late 2014. When completed, the mosque was the first in the state and one of the northernmost mosques in the world. There is also a Baháʼí center, and there were 690 adherents in 2020. Additionally, there were 469 adherents of Hinduism and Yoga altogether in 2020, and a small number of Buddhists were present.
Economy. As of October 2022, Alaska had a total employment of 316,900. The number of employer establishments was 21,077. The 2018 gross state product was $55 billion, 48th in the U.S. Its per capita personal income for 2018 was $73,000, ranking 7th in the nation. According to a 2013 study by Phoenix Marketing International, Alaska had the fifth-largest number of millionaires per capita in the United States, with a ratio of 6.75 percent. The oil and gas industry dominates the Alaskan economy, with more than 80% of the state's revenues derived from petroleum extraction. Alaska's main export product (excluding oil and natural gas) is seafood, primarily salmon, cod, pollock and crab. Agriculture represents a very small fraction of the Alaskan economy. Agricultural production is primarily for consumption within the state and includes nursery stock, dairy products, vegetables, and livestock. Manufacturing is limited, with most foodstuffs and general goods imported from elsewhere. Employment is primarily in government and industries such as natural resource extraction, shipping, and transportation. Military bases are a significant component of the economy in the Fairbanks North Star, Anchorage and Kodiak Island boroughs, as well as Kodiak. Federal subsidies are also an important part of the economy, allowing the state to keep taxes low. Its industrial outputs are crude petroleum, natural gas, coal, gold, precious metals, zinc and other mining, seafood processing, timber and wood products. There is also a growing service and tourism sector. Tourists have contributed to the economy by supporting local lodging.
Energy. Alaska has vast energy resources, although its oil reserves have been largely depleted. Major oil and gas reserves were found in the Alaska North Slope (ANS) and Cook Inlet basins, but according to the Energy Information Administration, by February 2014 Alaska had fallen to fourth place in the nation in crude oil production after Texas, North Dakota, and California. Prudhoe Bay on Alaska's North Slope is still the second highest-yielding oil field in the United States, typically producing about , although by early 2014 North Dakota's Bakken Formation was producing over . Prudhoe Bay was the largest conventional oil field ever discovered in North America, but was much smaller than Canada's enormous Athabasca oil sands field, which by 2014 was producing about of unconventional oil, and had hundreds of years of producible reserves at that rate. The Trans-Alaska Pipeline can transport and pump up to of crude oil per day, more than any other crude oil pipeline in the United States. Additionally, substantial coal deposits are found in Alaska's bituminous, sub-bituminous, and lignite coal basins. The United States Geological Survey estimates that there are of undiscovered, technically recoverable gas from natural gas hydrates on the Alaskan North Slope. Alaska also offers some of the highest hydroelectric power potential in the country from its numerous rivers. Large swaths of the Alaskan coastline offer wind and geothermal energy potential as well.
Alaska's economy depends heavily on increasingly expensive diesel fuel for heating, transportation, electric power and light. Although wind and hydroelectric power are abundant and underdeveloped, proposals for statewide energy systems were judged uneconomical (at the time of the report, 2001) due to low (less than 50¢/gal) fuel prices, long distances and low population. The cost of a gallon of gas in urban Alaska is usually thirty to sixty cents higher than the national average; prices in rural areas are generally significantly higher but vary widely depending on transportation costs, seasonal usage peaks, nearby petroleum development infrastructure and many other factors. Permanent Fund. The Alaska Permanent Fund is a constitutionally authorized appropriation of oil revenues, established by voters in 1976 to manage a surplus in state petroleum revenues from oil, largely in anticipation of the then recently constructed Trans-Alaska Pipeline System. The fund was originally proposed by Governor Keith Miller on the eve of the 1969 Prudhoe Bay lease sale, out of fear that the legislature would spend the entire proceeds of the sale (which amounted to $900 million) at once. It was later championed by Governor Jay Hammond and Kenai state representative Hugh Malone. It has served as an attractive political prospect ever since, diverting revenues which would normally be deposited into the general fund.
The Alaska Constitution was written so as to discourage dedicating state funds for a particular purpose. The Permanent Fund has become the rare exception to this, mostly due to the political climate of distrust existing during the time of its creation. From its initial principal of $734,000, the fund has grown to $50 billion as a result of oil royalties and capital investment programs. Most if not all the principal is invested conservatively outside Alaska. This has led to frequent calls by Alaskan politicians for the Fund to make investments within Alaska, though such a stance has never gained momentum. Starting in 1982, dividends from the fund's annual growth have been paid out each year to eligible Alaskans, ranging from an initial $1,000 in 1982 (equal to three years' payout, as the distribution of payments was held up in a lawsuit over the distribution scheme) to $3,269 in 2008 (which included a one-time $1,200 "Resource Rebate"). Every year, the state legislature takes out 8% from the earnings, puts 3% back into the principal for inflation proofing, and the remaining 5% is distributed to all qualifying Alaskans. To qualify for the Permanent Fund Dividend, one must have lived in the state for a minimum of 12 months, maintain constant residency subject to allowable absences, and not be subject to court judgments or criminal convictions which fall under various disqualifying classifications or may subject the payment amount to civil garnishment.
The Permanent Fund is often considered to be one of the leading examples of a basic income policy in the world. Cost of living. The cost of goods in Alaska has long been higher than in the contiguous 48 states. Federal government employees, particularly United States Postal Service (USPS) workers and active-duty military members, receive a Cost of Living Allowance usually set at 25% of base pay because, while the cost of living has gone down, it is still one of the highest in the country. Rural Alaska suffers from extremely high prices for food and consumer goods compared to the rest of the country, due to the relatively limited transportation infrastructure. Agriculture and fishing. Due to the northern climate and short growing season, relatively little farming occurs in Alaska. Most farms are in either the Matanuska Valley, about northeast of Anchorage, or on the Kenai Peninsula, about southwest of Anchorage. The short 100-day growing season limits the crops that can be grown, but the long sunny summer days make for productive growing seasons. The primary crops are potatoes, carrots, lettuce, and cabbage.
The Tanana Valley is another notable agricultural locus, especially the Delta Junction area, about southeast of Fairbanks, with a sizable concentration of farms growing agronomic crops; these farms mostly lie north and east of Fort Greely. This area was largely set aside and developed under a state program spearheaded by Hammond during his second term as governor. Delta-area crops consist predominantly of barley and hay. West of Fairbanks lies another concentration of small farms catering to restaurants, the hotel and tourist industry, and community-supported agriculture. Alaskan agriculture has experienced a surge in growth of market gardeners, small farms and farmers' markets in recent years, with the highest percentage increase (46%) in the nation in growth in farmers' markets in 2011, compared to 17% nationwide. The peony industry has also taken off, as the growing season allows farmers to harvest during a gap in supply elsewhere in the world, thereby filling a niche in the flower market. Alaska, with no counties, lacks county fairs. Instead, a small assortment of state and local fairs (with the Alaska State Fair in Palmer the largest), are held mostly in the late summer. The fairs are mostly located in communities with historic or current agricultural activity, and feature local farmers exhibiting produce in addition to more high-profile commercial activities such as carnival rides, concerts and food. "Alaska Grown" is used as an agricultural slogan.
Alaska has an abundance of seafood, with the primary fisheries in the Bering Sea and the North Pacific. Seafood is one of the few food items that is often cheaper within the state than outside it. Many Alaskans take advantage of salmon seasons to harvest portions of their household diet while fishing for subsistence, as well as sport. This includes fish taken by hook, net or wheel. Hunting for subsistence, primarily caribou, moose, and Dall sheep is still common in the state, particularly in remote Bush communities. An example of a traditional native food is Akutaq, the Eskimo ice cream, which can consist of reindeer fat, seal oil, dried fish meat and local berries. Alaska's reindeer herding is concentrated on Seward Peninsula, where wild caribou can be prevented from mingling and migrating with the domesticated reindeer. Most food in Alaska is transported into the state from "Outside" (the other 49 U.S. states), and shipping costs make food in the cities relatively expensive. In rural areas, subsistence hunting and gathering is an essential activity because imported food is prohibitively expensive. Although most small towns and villages in Alaska lie along the coastline, the cost of importing food to remote villages can be high because of the terrain and difficult road conditions, which change dramatically due to varying climate and precipitation changes. Transport costs can reach 50¢ per pound ($1.10/kg) or higher in some remote areas during times of inclement weather or rough terrain conditions, if these locations can be reached at all. The cost of delivering a gallon (3.8 L) of milk is about $3.50 in many villages where per capita income can be $20,000 or less. Fuel cost per gallon is routinely twenty to thirty cents higher than the contiguous United States average, with only Hawaii having higher prices.
Culture. Some of Alaska's popular annual events are the Iditarod Trail Sled Dog Race from Anchorage to Nome, World Ice Art Championships in Fairbanks, the Blueberry Festival and Alaska Hummingbird Festival in Ketchikan, the Sitka Whale Fest, and the Stikine River Garnet Fest in Wrangell. The Stikine River attracts the largest springtime concentration of American bald eagles in the world. The Alaska Native Heritage Center celebrates the rich heritage of Alaska's 11 cultural groups. Their purpose is to encourage cross-cultural exchanges among all people and enhance self-esteem among Native people. The Alaska Native Arts Foundation promotes and markets Native art from all regions and cultures in the State, using the internet. Music. Influences on music in Alaska include the traditional music of Alaska Natives as well as folk music brought by later immigrants from Russia and Europe. Prominent musicians from Alaska include singer Jewel, traditional Aleut flautist Mary Youngblood, folk singer-songwriter Libby Roderick, Christian music singer-songwriter Lincoln Brewster, metal/post hardcore band 36 Crazyfists and the groups Pamyua and Portugal. The Man.
There are many established music festivals in Alaska, including the Alaska Folk Festival, the Fairbanks Summer Arts Festival, the Anchorage Folk Festival, the Athabascan Old-Time Fiddling Festival, the Sitka Jazz Festival, the Sitka Summer Music Festival, and the Anchorage Chamber Music Festival. The most prominent orchestra in Alaska is the Anchorage Symphony Orchestra, though the Fairbanks Symphony Orchestra and Juneau Symphony are also notable. The Anchorage Opera is currently the state's only professional opera company, though there are several volunteer and semi-professional organizations in the state as well. The official state song of Alaska is "Alaska's Flag", which was adopted in 1955; it celebrates the flag of Alaska. Film and television. The 1983 Disney movie "Never Cry Wolf" was at least partially shot in Alaska. The 1991 film "White Fang", based on Jack London's 1906 novel and starring Ethan Hawke, was filmed in and around Haines. Steven Seagal's 1994 "On Deadly Ground", starring Michael Caine, was filmed in part at the Worthington Glacier near Valdez.
Many reality television shows are filmed in Alaska. In 2011, the "Anchorage Daily News" found ten set in the state. Sports. The following is a list of sporting venues, events, and teams based in Alaska. Public health and safety. The Alaska State Troopers are Alaska's statewide police force. They have a long and storied history, but were not an official organization until 1941. Before the force was officially organized, law enforcement in Alaska was handled by various federal agencies. Larger towns usually have their own local police and some villages rely on "Public Safety Officers" who have police training but do not carry firearms. In much of the state, the troopers serve as the only police force available. In addition to enforcing traffic and criminal law, wildlife Troopers enforce hunting and fishing regulations. Due to the varied terrain and wide scope of the Troopers' duties, they employ a wide variety of land, air, and water patrol vehicles. Many rural communities in Alaska are considered "dry", having outlawed the importation of alcoholic beverages. Suicide rates for rural residents are higher than urban.
Domestic abuse and other violent crimes are also at high levels in the state; this is in part linked to alcohol abuse. Alaska has the highest rate of sexual assault in the nation, especially in rural areas. The average age of sexually assaulted victims is 16 years old. In four out of five cases, the suspects were relatives, friends, or acquaintances. Health insurance. , CVS Health and Premera account for 47% and 46% of private health insurance, respectively. Premera and Moda Health offer insurance on the federally-run Affordable Care Exchange. Hospitals. Providence Alaska Medical Center in Anchorage is the largest hospital in the state as of 2021; Anchorage also hosts Alaska Regional Hospital and Alaska Native Medical Center. Alaska's other major cities such as Fairbanks and Juneau also have local hospitals. In Southeast Alaska, Southeast Alaska Regional Health Consortium, runs healthcare facilities across 27 communities as of 2022, including hospitals in Sitka and Wrangell; although it originally served Native Americans only, it has expanded access and combined with other local facilities over time.
Education. The Alaska Department of Education and Early Development administers many school districts in Alaska. In addition, the state operates a boarding school, Mt. Edgecumbe High School in Sitka, and provides partial funding for other boarding schools, including Nenana Student Living Center in Nenana and The Galena Interior Learning Academy in Galena. There are more than a dozen colleges and universities in Alaska. Accredited universities in Alaska include the University of Alaska Anchorage, University of Alaska Fairbanks, University of Alaska Southeast, and Alaska Pacific University. Alaska is the only state that has no collegiate athletic programs that are members of NCAA Division I, although both Alaska-Fairbanks and Alaska-Anchorage maintain single sport membership in Division I for men's ice hockey. The Alaska Department of Labor and Workforce Development operates AVTEC, Alaska's Institute of Technology. Campuses in Seward and Anchorage offer one-week to 11-month training programs in areas as diverse as Information Technology, Welding, Nursing, and Mechanics.
Alaska has had a problem with a "brain drain". Many of its young people, including most of the highest academic achievers, leave the state after high school graduation and do not return. , Alaska did not have a law school or medical school. The University of Alaska has attempted to combat this by offering partial four-year scholarships to the top 10% of Alaska high school graduates, via the Alaska Scholars Program. Beginning in 1998, schools in rural Alaska must have at least 10 students to retain funding from the state, and campuses not meeting the number close. This was due to the loss in oil revenues that previously propped up smaller rural schools. In 2015, there was a proposal to raise that minimum to 25, but legislators in the state largely did not agree. Transportation. Road. Alaska has few road connections compared to the rest of the U.S. The state's road system, covering a relatively small area of the state, linking the central population centers and the Alaska Highway, the principal route out of the state through Canada. The state capital, Juneau, is not accessible by road, with access only being through ferry or flight; this has spurred debate over decades about moving the capital to a city on the road system, or building a road connection from Haines. The western part of Alaska has no road system connecting the communities with the rest of Alaska.
The Interstate Highways in Alaska consists of a total of . One unique feature of the Alaska Highway system is the Anton Anderson Memorial Tunnel, an active Alaska Railroad tunnel recently upgraded to provide a paved roadway link with the isolated community of Whittier on Prince William Sound to the Seward Highway about southeast of Anchorage at Portage. At , the tunnel was the longest road tunnel in North America until 2007. The tunnel is the longest combination road and rail tunnel in North America. Southwest Alaska is largely coastal, sparsely populated, and unconnected to the road system. Access to most communities in Southwest Alaska is primarily by air taxi, although larger towns like Kodiak, Bethel, King Salmon, Dillingham, and Dutch Harbor are accessible by scheduled air service. Additionally, some coastal communities can be reached via the Alaska Marine Highway ferry. Rail. Built around 1915, the Alaska Railroad (ARR) played a key role in the development of Alaska through the 20th century. It links shipping lanes on the North Pacific with Interior Alaska with tracks that run from Seward by way of South Central Alaska, passing through Anchorage, Eklutna, Wasilla, Talkeetna, Denali, and Fairbanks, with spurs to Whittier, Palmer and North Pole. The cities, towns, villages, and region served by ARR tracks are known statewide as "The Railbelt". In recent years, the ever-improving paved highway system began to eclipse the railroad's importance in Alaska's economy.
The railroad played a vital role in Alaska's development, moving freight into Alaska while transporting natural resources southward, such as coal from the Usibelli coal mine near Healy to Seward and gravel from the Matanuska Valley to Anchorage. It is well known for its summertime tour passenger service. The Alaska Railroad was one of the last railroads in North America to use cabooses in regular service and still uses them on some gravel trains. It continues to offer one of the last flag stop routes in the country. A stretch of about of track along an area north of Talkeetna remains inaccessible by road; the railroad provides the only transportation to rural homes and cabins in the area. Until construction of the Parks Highway in the 1970s, the railroad provided the only land access to most of the region along its entire route. In northern Southeast Alaska, the White Pass and Yukon Route also partly runs through the state from Skagway northwards into Canada (British Columbia and Yukon Territory), crossing the border at White Pass Summit. This line is now mainly used by tourists, often arriving by cruise liner at Skagway. It was featured in the 1983 BBC television series "Great Little Railways."
These two railroads are connected neither to each other nor any other railroad. The nearest link to the North American railway network is the northwest terminus of the Canadian National Railway at Prince Rupert, British Columbia, several hundred miles to the southeast. In 2000, the U.S. Congress authorized $6 million to study the feasibility of a rail link between Alaska, Canada, and the lower 48. As of 2021, the Alaska-Alberta Railway Development Corporation had been placed into receivership. Some private companies provides car float service between Whittier and Seattle. Sea. Many cities, towns, and villages in the state do not have road or highway access; the only modes of access involve travel by air, river, or the sea. Alaska's well-developed state-owned ferry system (known as the Alaska Marine Highway) serves the cities of southeast, the Gulf Coast and the Alaska Peninsula. The ferries transport vehicles as well as passengers. The system also operates a ferry service from Bellingham, Washington and Prince Rupert, British Columbia, in Canada through the Inside Passage to Skagway. The Inter-Island Ferry Authority also serves as an important marine link for many communities in the Prince of Wales Island region of Southeast and works in concert with the Alaska Marine Highway.
In recent years, cruise lines have created a summertime tourism market, mainly connecting the Pacific Northwest to Southeast Alaska and, to a lesser degree, towns along Alaska's gulf coast. The population of Ketchikan for example fluctuates dramatically on many days—up to four large cruise ships can dock there at the same time. Air. Cities not served by road, sea, or river can be reached only by air, foot, dogsled, or snowmachine, accounting for Alaska's extremely well developed bush air services—an Alaskan novelty. Anchorage, and to a lesser extent Fairbanks, is served by many major airlines. Because of limited highway access, air travel remains the most efficient form of transportation in and out of the state. Anchorage recently completed extensive remodeling and construction at Ted Stevens Anchorage International Airport to help accommodate the upsurge in tourism (in 2012–2013, Alaska received almost two million visitors). Making regular flights to most villages and towns within the state commercially viable is difficult, so they are heavily subsidized by the federal government through the Essential Air Service program. Alaska Airlines is the only major airline offering in-state travel with jet service (sometimes in combination cargo and passenger Boeing 737-400s) from Anchorage and Fairbanks to regional hubs like Bethel, Nome, Kotzebue, Dillingham, Kodiak, and other larger communities as well as to major Southeast and Alaska Peninsula communities.
The bulk of remaining commercial flight offerings come from small regional commuter airlines such as Ravn Alaska, PenAir, and Frontier Flying Service. The smallest towns and villages must rely on scheduled or chartered bush flying services using general aviation aircraft such as the Cessna Caravan, the most popular aircraft in use in the state. Much of this service can be attributed to the Alaska bypass mail program which subsidizes bulk mail delivery to Alaskan rural communities. The program requires 70% of that subsidy to go to carriers who offer passenger service to the communities. Many communities have small air taxi services. These operations originated from the demand for customized transport to remote areas. Perhaps the most quintessentially Alaskan plane is the bush seaplane. The world's busiest seaplane base is Lake Hood, located next to Ted Stevens Anchorage International Airport, where flights bound for remote villages without an airstrip carry passengers, cargo, and many items from stores and warehouse clubs.
In 2006, Alaska had the highest number of pilots per capita of any U.S. state. In Alaska there are 8,795 active pilot certificates as of 2020. Snow. Another Alaskan transportation method is the dogsled. In modern times (that is, any time after the mid-late 1920s), dog mushing is more of a sport than a true means of transportation. Various races are held around the state, but the best known is the Iditarod Trail Sled Dog Race, a trail from Anchorage to Nome (although the distance varies from year to year, the official distance is set at ). The race commemorates the famous 1925 serum run to Nome in which mushers and dogs like Togo and Balto took much-needed medicine to the diphtheria-stricken community of Nome when all other means of transportation had failed. Mushers from all over the world come to Anchorage each March to compete for cash, prizes, and prestige. The "Serum Run" is another sled dog race that more accurately follows the route of the famous 1925 relay, leaving from the community of Nenana (southwest of Fairbanks) to Nome.
In areas not served by road or rail, primary transportation in summer is by all-terrain vehicle and in winter by snowmobile or "snow machine", as it is commonly referred to in Alaska. Communication. Alaska's internet and other data transport systems are provided largely through the two major telecommunications companies: GCI and Alaska Communications. GCI owns and operates what it calls the Alaska United Fiber Optic system and, as of late 2011, Alaska Communications advertised that it has "two fiber optic paths to the lower 48 and two more across Alaska. In January 2011, it was reported that a $1 billion project to connect Asia and rural Alaska was being planned, aided in part by $350 million in stimulus from the federal government. Law and government. State government. Like all other U.S. states, Alaska is governed as a republic, with three branches of government: an executive branch consisting of the governor of Alaska and their appointees which head executive departments; a legislative branch consisting of the Alaska House of Representatives and Alaska Senate; and a judicial branch consisting of the Alaska Supreme Court and lower courts.
The state of Alaska employs approximately 16,000 people statewide. The Alaska State Legislature consists of a 40-member House of Representatives and a 20-member Senate. Senators serve four-year terms and House members two. The governor of Alaska serves four-year terms. The lieutenant governor runs separately from the governor in the primaries, but during the general election, the nominee for governor and nominee for lieutenant governor run together on the same ticket. Alaska's court system has four levels: the Alaska Supreme Court, the Alaska Court of Appeals, the superior courts and the district courts. The superior and district courts are trial courts. Superior courts are courts of general jurisdiction, while district courts hear only certain types of cases, including misdemeanor criminal cases and civil cases valued up to $100,000. The Supreme Court and the Court of Appeals are appellate courts. The Court of Appeals is required to hear appeals from certain lower-court decisions, including those regarding criminal prosecutions, juvenile delinquency, and habeas corpus. The Supreme Court hears civil appeals and may in its discretion hear criminal appeals.
State politics. Although in its early years of statehood Alaska was a Democratic state, since the early 1970s it has been characterized as Republican-leaning. Local political communities have often worked on issues related to land use development, fishing, tourism, and individual rights. Alaska Natives, while organized in and around their communities, have been active within the Native corporations. These have been given ownership over large tracts of land, which require stewardship. Alaska was formerly the only state in which possession of one ounce or less of marijuana in one's home was completely legal under state law, though the federal law remains in force. The state has an independence movement favoring a vote on secession from the United States, with the Alaskan Independence Party. Six Republicans and four Democrats have served as governor of Alaska. In addition, Republican governor Wally Hickel was elected to the office for a second term in 1990 after leaving the Republican party and briefly joining the Alaskan Independence Party ticket just long enough to be reelected. He officially rejoined the Republican party in 1994.
Alaska's voter initiative making marijuana legal took effect on February 24, 2015, placing Alaska alongside Colorado and Washington, as well as Washington D.C., as the first three U.S. states where recreational marijuana is legal. The new law means people over 21 can consume small amounts of cannabis. The first legal marijuana store opened in Valdez in October 2016. Taxes. To finance state government operations, Alaska depends primarily on petroleum revenues and federal subsidies. This allows it to have the lowest individual tax burden in the United States. It is one of five states with no sales tax, one of seven states with no individual income tax, and—along with New Hampshire—one of two that has neither. The Department of Revenue Tax Division reports regularly on the state's revenue sources. The department also issues an annual summary of its operations, including new state laws that directly affect the tax division. In 2014, the Tax Foundation ranked Alaska as having the fourth most "business friendly" tax policy, behind only Wyoming, South Dakota, and Nevada.
While Alaska has no state sales tax, 89 municipalities collect a local sales tax, from 1.0 to 7.5%, typically 3–5%. Other local taxes levied include raw fish taxes, hotel, motel, and bed-and-breakfast 'bed' taxes, severance taxes, liquor and tobacco taxes, gaming (pull tabs) taxes, tire taxes and fuel transfer taxes. A part of the revenue collected from certain state taxes and license fees (such as petroleum, aviation motor fuel, telephone cooperative) is shared with municipalities in Alaska. The fall in oil prices after the fracking boom in the early 2010s has decimated Alaska's state treasury, which has historically received about 85 percent of its revenue from taxes and fees imposed on oil and gas companies. The state government has had to drastically reduce its budget, and has brought its budget shortfall from over $2 billion in 2016 to under $500 million by 2018. In 2020, Alaska's state government budget was $4.8 billion, while projected government revenues were only $4.5 billion. Federal politics. Alaska regularly supports Republicans in presidential elections and has done so since statehood. Republicans have won the state's electoral college votes in all but one election that it has participated in (1964). No state has voted for a Democratic presidential candidate fewer times. Alaska was carried by Democratic nominee Lyndon B. Johnson during his landslide election in 1964, while the 1960 and 1968 elections were close. Since 1972, Republicans have carried the state by large margins. In 2008, Republican John McCain defeated Democrat Barack Obama in Alaska, 59.49% to 37.83%. McCain's running mate was Sarah Palin, the state's governor and the first Alaskan on a major party ticket. Obama lost Alaska again in 2012, but he captured 40% of the state's vote in that election, making him the first Democrat to do so since 1968. In 2020, Joe Biden received 42.77% of the vote for president, marking the high point for a Democratic presidential candidate since Johnson's 1964 victory.
The Alaska Bush, central Juneau, midtown and downtown Anchorage, and the areas surrounding the University of Alaska Fairbanks campus and Ester have been strongholds of the Democratic Party. The Matanuska-Susitna Borough, the majority of Fairbanks (including North Pole and the military base), and South Anchorage typically have the strongest Republican showing. Elections. Alaska has a history of primary defeats for incumbent U.S. Senators, including Ernest Gruening, Mike Gravel, and Lisa Murkowski. However, Murkowski won re-election with a write-in campaign. Despite this, Alaska has also seen long-serving members of Congress, such as Ted Stevens, who served as a U.S. Senator for 40 years, and Don Young, who held Alaska's sole U.S. House seat for 49 years (from 1973 to 2022). In the 2020 election cycle, Alaskan voters approved Ballot Measure 2. The measure passed by a margin of 1.1%, or about 4,000 votes. The measure requires campaigns to disclose the original source and any intermediaries for campaign contributions over $2,000. The measure also establishes non-partisan primaries, sometimes called jungle primaries, for statewide elections (like in Washington state and California) and ranked-choice voting (like in Maine). Measure 2 makes Alaska the third state with nonpartisan primaries for all statewide races, the second state with ranked choice voting, and the only state with both. The 2022 special election to fill Alaska's only U.S. House seat, left vacant by the death of Don Young, was won by Mary Peltola. She became the first Democrat to win the House seat since 1972 and the first Alaskan Native elected to the United States Congress in history. After winning a full term in the 2022 general election, Peltola lost reelection in 2024 to Republican Nick Begich III.
Agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to live in the cities. While humans started gathering grains at least 105,000 years ago, nascent farmers only began planting them around 11,500 years ago. Sheep, goats, pigs, and cattle were domesticated around 10,000 years ago. Plants were independently cultivated in at least 11 regions of the world. In the 20th century, industrial agriculture based on large-scale monocultures came to dominate agricultural output. , small farms produce about one-third of the world's food, but large farms are prevalent. The largest 1% of farms in the world are greater than and operate more than 70% of the world's farmland. Nearly 40% of agricultural land is found on farms larger than . However, five of every six farms in the world consist of fewer than , and take up only around 12% of all agricultural land. Farms and farming greatly influence rural economics and greatly shape rural society, affecting both the direct agricultural workforce and broader businesses that support the farms and farming populations.
The major agricultural products can be broadly grouped into foods, fibers, fuels, and raw materials (such as rubber). Food classes include cereals (grains), vegetables, fruits, cooking oils, meat, milk, eggs, and fungi. Global agricultural production amounts to approximately 11 billion tonnes of food, 32 million tonnes of natural fibers and 4 billion m3 of wood. However, around 14% of the world's food is lost from production before reaching the retail level. Modern agronomy, plant breeding, agrochemicals such as pesticides and fertilizers, and technological developments have sharply increased crop yields, but also contributed to ecological and environmental damage. Selective breeding and modern practices in animal husbandry have similarly increased the output of meat, but have raised concerns about animal welfare and environmental damage. Environmental issues include contributions to climate change, depletion of aquifers, deforestation, antibiotic resistance, and other agricultural pollution. Agriculture is both a cause of and sensitive to environmental degradation, such as biodiversity loss, desertification, soil degradation, and climate change, all of which can cause decreases in crop yield. Genetically modified organisms are widely used, although some countries ban them.
Etymology and scope. The word "agriculture" is a late Middle English adaptation of Latin , from 'field' and 'cultivation' or 'growing'. While agriculture usually refers to human activities, certain species of ant, termite and beetle have been cultivating crops for up to 60 million years. Agriculture is defined with varying scopes, in its broadest sense using natural resources to "produce commodities which maintain life, including food, fiber, forest products, horticultural crops, and their related services". Thus defined, it includes arable farming, horticulture, animal husbandry and forestry, but horticulture and forestry are in practice often excluded. It may also be broadly decomposed into plant agriculture, which concerns the cultivation of useful plants, and animal agriculture, the production of agricultural animals. History. Origins.
Scholars have offered multiple hypotheses to explain the historical origins of agriculture. Studies of the transition from hunter-gatherer to agricultural societies indicate an initial period of intensification and increasing sedentism; examples are the Natufian culture in the Levant, and the Early Chinese Neolithic in China. Then, wild stands that had previously been harvested started to be planted, and gradually came to be domesticated. Civilizations. In Eurasia, the Sumerians started to live in villages from about 8,000 BC, relying on the Tigris and Euphrates rivers and a canal system for irrigation. Ploughs appear in pictographs around 3,000 BC; seed-ploughs around 2,300 BC. Farmers grew wheat, barley, vegetables such as lentils and onions, and fruits including dates, grapes, and figs. Ancient Egyptian agriculture relied on the Nile River and its seasonal flooding. Farming started in the predynastic period at the end of the Paleolithic, after 10,000 BC. Staple food crops were grains such as wheat and barley, alongside industrial crops such as flax and papyrus. In India, wheat, barley and jujube were domesticated by 9,000 BC, soon followed by sheep and goats. Cattle, sheep and goats were domesticated in Mehrgarh culture by 8,000–6,000 BC. Cotton was cultivated by the 5th–4th millennium BC. Archeological evidence indicates an animal-drawn plough from 2,500 BC in the Indus Valley civilization.
In China, from the 5th century BC, there was a nationwide granary system and widespread silk farming. Water-powered grain mills were in use by the 1st century BC, followed by irrigation. By the late 2nd century, heavy ploughs had been developed with iron ploughshares and mouldboards. These spread westwards across Eurasia. Asian rice was domesticated 8,200–13,500 years ago – depending on the molecular clock estimate that is used– on the Pearl River in southern China with a single genetic origin from the wild rice "Oryza rufipogon". In Greece and Rome, the major cereals were wheat, emmer, and barley, alongside vegetables including peas, beans, and olives. Sheep and goats were kept mainly for dairy products. In the Americas, crops domesticated in Mesoamerica (apart from teosinte) include squash, beans, and cacao. Cocoa was domesticated by the Mayo Chinchipe of the upper Amazon around 3,000 BC.
Indigenous Australians, long supposed to have been nomadic hunter-gatherers, practiced systematic burning, possibly to enhance natural productivity in fire-stick farming. Scholars have pointed out that hunter-gatherers need a productive environment to support gathering without cultivation. Because the forests of New Guinea have few food plants, early humans may have used "selective burning" to increase the productivity of the wild karuka fruit trees to support the hunter-gatherer way of life. The Gunditjmara and other groups developed eel farming and fish trapping systems from some 5,000 years ago. There is evidence of 'intensification' across the whole continent over that period. In two regions of Australia, the central west coast and eastern central, early farmers cultivated yams, native millet, and bush onions, possibly in permanent settlements. Revolution. In the Middle Ages, compared to the Roman period, agriculture in Western Europe became more focused on self-sufficiency. The agricultural population under feudalism was typically organized into manors consisting of several hundred or more acres of land presided over by a lord of the manor with a Roman Catholic church and priest.
Thanks to the exchange with the Al-Andalus where the Arab Agricultural Revolution was underway, European agriculture transformed, with improved techniques and the diffusion of crop plants, including the introduction of sugar, rice, cotton and fruit trees (such as the orange). After 1492, the Columbian exchange brought New World crops such as maize, potatoes, tomatoes, sweet potatoes, and manioc to Europe, and Old World crops such as wheat, barley, rice, and turnips, and livestock (including horses, cattle, sheep and goats) to the Americas. Irrigation, crop rotation, and fertilizers advanced from the 17th century with the British Agricultural Revolution, allowing global population to rise significantly. Since 1900, agriculture in developed nations, and to a lesser extent in the developing world, has seen large rises in productivity as mechanization replaces human labor, and assisted by synthetic fertilizers, pesticides, and selective breeding. The Haber-Bosch method allowed the synthesis of ammonium nitrate fertilizer on an industrial scale, greatly increasing crop yields and sustaining a further increase in global population.
Modern agriculture has raised or encountered ecological, political, and economic issues including water pollution, biofuels, genetically modified organisms, tariffs and farm subsidies, leading to alternative approaches such as the organic movement. Unsustainable farming practices in North America led to the Dust Bowl of the 1930s. Types. Pastoralism involves managing domesticated animals. In nomadic pastoralism, herds of livestock are moved from place to place in search of pasture, fodder, and water. This type of farming is practiced in arid and semi-arid regions of Sahara, Central Asia and some parts of India. In shifting cultivation, a small area of forest is cleared by cutting and burning the trees. The cleared land is used for growing crops for a few years until the soil becomes too infertile, and the area is abandoned. Another patch of land is selected and the process is repeated. This type of farming is practiced mainly in areas with abundant rainfall where the forest regenerates quickly. This practice is used in Northeast India, Southeast Asia, and the Amazon Basin.
Subsistence farming is practiced to satisfy family or local needs alone, with little left over for transport elsewhere. It is intensively practiced in Monsoon Asia and South-East Asia. An estimated 2.5 billion subsistence farmers worked in 2018, cultivating about 60% of the earth's arable land. Intensive farming is cultivation to maximize productivity, with a low fallow ratio and a high use of inputs (water, fertilizer, pesticide and automation). It is practiced mainly in developed countries. Contemporary agriculture. Status. From the twentieth century onwards, intensive agriculture increased crop productivity. It substituted synthetic fertilizers and pesticides for labor, but caused increased water pollution, and often involved farm subsidies. Soil degradation and diseases such as stem rust are major concerns globally; approximately 40% of the world's agricultural land is seriously degraded. In recent years there has been a backlash against the environmental effects of conventional agriculture, resulting in the organic, regenerative, and sustainable agriculture movements. One of the major forces behind this movement has been the European Union, which first certified organic food in 1991 and began reform of its Common Agricultural Policy (CAP) in 2005 to phase out commodity-linked farm subsidies, also known as decoupling. The growth of organic farming has renewed research in alternative technologies such as integrated pest management, selective breeding, and controlled-environment agriculture. There are concerns about the lower yield associated with organic farming and its impact on global food security. Recent mainstream technological developments include genetically modified food.
By 2015, the agricultural output of China was the largest in the world, followed by the European Union, India and the United States. Economists measure the total factor productivity of agriculture, according to which agriculture in the United States is roughly 1.7 times more productive than it was in 1948. Agriculture employed 873 million people in 2021, or 27% of the global workforce, compared with 1 027 million (or 40%) in 2000. The share of agriculture in global GDP was stable at around 4% since 2000–2023. Despite increases in agricultural production and productivity, between 702 and 828 million people were affected by hunger in 2021. Food insecurity and malnutrition can be the result of conflict, climate extremes and variability and economic swings. It can also be caused by a country's structural characteristics such as income status and natural resource endowments as well as its political economy. Pesticide use in agriculture went up 62% between 2000 and 2021, with the Americas accounting for half the use in 2021.
The International Fund for Agricultural Development posits that an increase in smallholder agriculture may be part of the solution to concerns about food prices and overall food security, given the favorable experience of Vietnam. Workforce. Agriculture provides about one-quarter of all global employment, more than half in sub-Saharan Africa and almost 60 percent in low-income countries. As countries develop, other jobs have historically pulled workers away from agriculture, and labor-saving innovations increase agricultural productivity by reducing labor requirements per unit of output. Over time, a combination of labor supply and labor demand trends have driven down the share of population employed in agriculture. During the 16th century in Europe, between 55 and 75% of the population was engaged in agriculture; by the 19th century, this had dropped to between 35 and 65%. In the same countries today, the figure is less than 10%. At the start of the 21st century, some one billion people, or over 1/3 of the available work force, were employed in agriculture. This constitutes approximately 70% of the global employment of children, and in many countries constitutes the largest percentage of women of any industry. The service sector overtook the agricultural sector as the largest global employer in 2007.
In many developed countries, immigrants help fill labor shortages in high-value agriculture activities that are difficult to mechanize. Foreign farm workers from mostly Eastern Europe, North Africa and South Asia constituted around one-third of the salaried agricultural workforce in Spain, Italy, Greece and Portugal in 2013. In the United States of America, more than half of all hired farmworkers (roughly 450,000 workers) were immigrants in 2019, although the number of new immigrants arriving in the country to work in agriculture has fallen by 75 percent in recent years and rising wages indicate this has led to a major labor shortage on U.S. farms. Women in agriculture. Around the world, women make up a large share of the population employed in agriculture. This share is growing in all developing regions except East and Southeast Asia where women already make up about 50 percent of the agricultural workforce. Women make up 47 percent of the agricultural workforce in sub-Saharan Africa, a rate that has not changed significantly in the past few decades. However, the Food and Agriculture Organization of the United Nations (FAO) posits that the roles and responsibilities of women in agriculture may be changing – for example, from subsistence farming to wage employment, and from contributing household members to primary producers in the context of male-out-migration.
In general, women account for a greater share of agricultural employment at lower levels of economic development, as inadequate education, limited access to basic infrastructure and markets, high unpaid work burden and poor rural employment opportunities outside agriculture severely limit women's opportunities for off-farm work. Women who work in agricultural production tend to do so under highly unfavorable conditions. They tend to be concentrated in the poorest countries, where alternative livelihoods are not available, and they maintain the intensity of their work in conditions of climate-induced weather shocks and in situations of conflict. Women are less likely to participate as entrepreneurs and independent farmers and are engaged in the production of less lucrative crops. The gender gap in land productivity between female- and male managed farms of the same size is 24 percent. On average, women earn 18.4 percent less than men in wage employment in agriculture; this means that women receive 82 cents for every dollar earned by men. Progress has been slow in closing gaps in women's access to irrigation and in ownership of livestock, too.
Women in agriculture still have significantly less access than men to inputs, including improved seeds, fertilizers and mechanized equipment. On a positive note, the gender gap in access to mobile internet in low- and middle-income countries fell from 25 percent to 16 percent between 2017 and 2021, and the gender gap in access to bank accounts narrowed from 9 to 6 percentage points. Women are as likely as men to adopt new technologies when the necessary enabling factors are put in place and they have equal access to complementary resources. Safety. Agriculture, specifically farming, remains a hazardous industry, and farmers worldwide remain at high risk of work-related injuries, lung disease, noise-induced hearing loss, skin diseases, as well as certain cancers related to chemical use and prolonged sun exposure. On industrialized farms, injuries frequently involve the use of agricultural machinery, and a common cause of fatal agricultural injuries in developed countries is tractor rollovers. Pesticides and other chemicals used in farming can be hazardous to worker health, and workers exposed to pesticides may experience illness or have children with birth defects. As an industry in which families commonly share in work and live on the farm itself, entire families can be at risk for injuries, illness, and death. Ages 0–6 may be an especially vulnerable population in agriculture; common causes of fatal injuries among young farm workers include drowning, machinery and motor accidents, including with all-terrain vehicles.
The International Labor Organization considers agriculture "one of the most hazardous of all economic sectors". It estimates that the annual work-related death toll among agricultural employees is at least 170,000, twice the average rate of other jobs. In addition, incidences of death, injury and illness related to agricultural activities often go unreported. The organization has developed the Safety and Health in Agriculture Convention, 2001, which covers the range of risks in the agriculture occupation, the prevention of these risks and the role that individuals and organizations engaged in agriculture should play. In the United States, agriculture has been identified by the National Institute for Occupational Safety and Health as a priority industry sector in the National Occupational Research Agenda to identify and provide intervention strategies for occupational health and safety issues. In the European Union, the European Agency for Safety and Health at Work has issued guidelines on implementing health and safety directives in agriculture, livestock farming, horticulture, and forestry. The Agricultural Safety and Health Council of America (ASHCA) also holds a yearly summit to discuss safety.
Production. Overall production varies by country as listed. Crop cultivation systems. Cropping systems vary among farms depending on the available resources and constraints; geography and climate of the farm; government policy; economic, social and political pressures; and the philosophy and culture of the farmer. Shifting cultivation (or slash and burn) is a system in which forests are burnt, releasing nutrients to support cultivation of annual and then perennial crops for a period of several years. Then the plot is left fallow to regrow forest, and the farmer moves to a new plot, returning after many more years (10–20). This fallow period is shortened if population density grows, requiring the input of nutrients (fertilizer or manure) and some manual pest control. Annual cultivation is the next phase of intensity in which there is no fallow period. This requires even greater nutrient and pest control inputs. Further industrialization led to the use of monocultures, when one cultivar is planted on a large acreage. Because of the low biodiversity, nutrient use is uniform and pests tend to build up, necessitating the greater use of pesticides and fertilizers. Multiple cropping, in which several crops are grown sequentially in one year, and intercropping, when several crops are grown at the same time, are other kinds of annual cropping systems known as polycultures.
In subtropical and arid environments, the timing and extent of agriculture may be limited by rainfall, either not allowing multiple annual crops in a year, or requiring irrigation. In all of these environments perennial crops are grown (coffee, chocolate) and systems are practiced such as agroforestry. In temperate environments, where ecosystems were predominantly grassland or prairie, highly productive annual farming is the dominant agricultural system. Important categories of food crops include cereals, legumes, forage, fruits and vegetables. Natural fibers include cotton, wool, hemp, silk and flax. Specific crops are cultivated in distinct growing regions throughout the world. Production is listed in millions of metric tons, based on FAO estimates. Livestock production systems. Animal husbandry is the breeding and raising of animals for meat, milk, eggs, or wool, and for work and transport. Working animals, including horses, mules, oxen, water buffalo, camels, llamas, alpacas, donkeys, and dogs, have for centuries been used to help cultivate fields, harvest crops, wrangle other animals, and transport farm products to buyers.

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