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and thus ancestor to A. afarensis and all other australopithecines. Differing Views of the Hominid Family Tree (a.5 1 1.5 2 2.5 3 3.5 4 4.5 (b) H. sapiens H. neanderthalensis H. erectus H. heidelbergensis H. ergaster H. habilis A. robustus A. boisei H. rudolfensis A. africanus Classified by some scientists as the sing...
to be A. afarensis. Only within the last 30 years have a significant number of fossils of early Homo been uncovered. An explosion of interest has fueled intensive field exploration in the last few years, and new finds are announced regularly; every year, our picture of the base of the human evolutionary tree grows cle...
years old and has been assigned to the species Homo ergaster (a form of Homo habilis recognized by some as a separate species). Much larger than earlier hominids, he was about 1.5 meters in height and weighed approximately 47 kilograms. How Diverse Was Early Homo? Because so few fossils have been found of early Homo, ...
that time, and few scientists were willing to accept that it was an ancient species of human. Peking Man Another generation passed before scientists were forced to admit that Dubois had been right all along. In the 1920s a skull was discovered near Peking (now Beijing), China, that closely resembled Java man. Continue...
H. habilis, H. erectus quickly became widespread and abundant in Africa, and within 1 million years had migrated into Asia and Europe. A social species, H. erectus lived in tribes of 20 to 50 people, often dwelling in caves. They successfully hunted large animals, butchered them using flint and bone tools, and cooked ...
,000 years old. Other fossils from Israel appear to be between 100,000 and 120,000 years old. Outside of Africa and the Middle East, there are no clearly dated H. sapiens fossils older than roughly 40,000 years of age. The implication is that H. sapiens evolved in Africa, then migrated to Europe and Asia, the Out-of-Af...
China. Later, H. erectus was followed and replaced by Homo neanderthalensis, a pattern repeated again still later by Homo sapiens (red arrow). H. sapiens (Cro-Magnon) H. neanderthalensis FIGURE 23.13 (continued) Chapter 23 How Humans Evolved 489 Our Own Species: Homo sapiens H. sapiens is the only surviving species of...
social organization and are thought to have had full language capabilities. They lived by hunting. The world was cooler than it is now—the time of the last great ice age—and Europe was covered with grasslands inhabited by large herds of grazing animals. Pictures of them can be seen in elaborate and often beautiful cav...
, and dark skin shields the body from the damaging effects of ultraviolet radiation, which is much stronger in the tropics than in temperate regions. All human beings are capable of mating with one another and producing fertile offspring. The reasons that they do or do not choose to associate with one another are purel...
. The code below the figure is arranged in order of similarity. (b) Similarity among Homo sapiens based on skin color. The categories are arranged by amount of pigmentation in the skin. For this reason, relatively little of the variation in the human species represents differences between the described races. Indeed, o...
genus Homo evolved in Africa. • Hominids with an enlarged brain and the ability to use tools belong to the genus Homo. Species of early Homo appeared in Africa about 2 million years ago and became extinct about 1.5 million years ago. • Homo erectus appeared in Africa at least 1.5 million years ago and had a much large...
of these odd generalizations: songbirds in the tropics lay fewer eggs than their counterparts at higher latitudes (see above right). Tropical songbirds typically lay a clutch of 2 or 3 eggs, on average, while songbirds in temperate and subarctic regions generally lay clutches of 4 to 6 eggs, and some species as many a...
maximizes the number of offspring which are fed enough to survive to maturity. The driving force behind Lack’s theory of optimal clutch size is his idea that broods with too many offspring would be undernourished, reducing the probability that the chicks would survive. In Lack’s own words: “The average clutch-size is ...
was completed in 1987 in the woods near Oxford, England. Over many years, Oxford University researchers led by Professor Mark Boyce (now at the University of Wyoming, Laramie) carefully monitored nests of a songbird, the greater tit, very common in the English countryside. They counted the number of eggs laid in each ...
a population can be clumped, random, or even. Metapopulations. Sometimes, populations are arranged in networks connected by the exchange of individuals. 24.2 Population dynamics depend critically upon age distribution. Demography. The growth rate of a population is a sensitive function of its age structure; population...
focus for our inquiry. A population consists of the individuals of a given species that occur together at one place and time. This flexible definition allows us to speak in similar terms of the world’s human population, the population of protozoa in the gut of an individual termite, or the population of deer that inha...
white rhinoceros 496 Part VII Ecology and Behavior 15,000 years ago Present ) km 2 km 1 km Alpine tundra Spruce-fir forests Mixed conifer forest Woodlands 0 km Grassland, chaparral, and desert scrub Alpine tundra Spruce-fir forests Mixed conifer forest Woodlands Grassland, chaparral, and desert scrub FIGURE 24.3 Altit...
, or clumped (figure 24.5). Randomly spaced (a) Bacterial colonies Random Uniform Clumped Individuals are randomly spaced within populations when they do not interact strongly with one another or with nonuniform aspects of their microenvironment. Random distributions are not common in nature. Some species of trees, how...
• •••••• ••• • •• • ••• • •• ••• • • • ••• • • • • • • •• ••• • • ••• • ••• • • • •••• • ••• ••••••• •••• • • •••••• •••• •• •••••• •• • ••• •••• ••• • • •• •• •• • ••• ••••• ••• • • • •• • •• • • • •• • •• • •••••• • • ••••••• •••• •• • •••• •• • • • •• ••••••••• • •• • • • • ••• • •••• • • •• ••• •• ••• • •• • •••••...
•••••••• ••••••••••• •••• • • • • • • • • • • •• • • • •• • • • • • •••••••• ••• •••• • • • • • • • • • • • • • •••••• • • • • • (d) Clumped distribution of Chamguava schippii Windblown fruits Adherent fruits Fleshy fruits FIGURE 24.6 Some of the many adaptations of seeds to facilitate dispersal. Seeds have evolved a n...
Their population steadily spread such that by 1980, they occurred throughout the United States. Similar stories could be told for countless numbers of plants and animals, and the list increases every year. Unfortunately, the success of these invaders often comes at the expense of native species. Dispersal Mechanisms D...
extinction of existing populations is balanced by the rate of colonization of empty habitats. A second type of metapopulation structure occurs in areas in which some habitats are suitable for long-term population maintenance, whereas others are not. In these situations, termed source-sink metapopulations, the populati...
ink metapopulations, the species as a whole occupies a larger area than it otherwise might occupy. For these reasons, the study of metapopulations has become very important in conservation biology as natural habitats become increasingly fragmented. The distribution of individuals within a population can be random, unif...
ice go through approximately 100 generations during the course of one elephant generation—but not all of it (figure 24.8). Newts, for example, are smaller than mice, but have considerably longer generation times. Everything else equal, populations with shorter generations can increase in size more quickly than populati...
to assess how populations in nature are changing. Life tables can be constructed by following the fate of a cohort from birth until death, noting the number of offspring produced and individuals that die each year. A very nice example of a life table analysis is exhibited in a study of the meadow grass Poa annua. This...
have been produced. A figure of 1.0 would be the breakeven number, the point at which the population was neither growing nor shrinking. In this case, the population appears to be growing rapidly. In most cases, life table analysis is more complicated than this. First, except for organisms with short life spans, it is ...
cohort of the meadow grass, Poa annua. Mortality increases at a constant rate through time. Chapter 24 Population Ecology 503 24.3 Life histories often reflect trade-offs between reproduction and survival. Natural selection favors traits that maximize the number of surviving offspring left in the next generation. Two ...
of increased reproductive efforts may not make a difference in future survival. 504 Part VII Ecology and Behavior.5 0.2 0.1 0.05 0.1 0.2 0.5 1.0 Annual adult mortality rate FIGURE 24.11 Reproduction has a price. Increased fecundity in birds correlates with higher mortality in several populations of birds ranging from ...
between clutch size and parental investment discussed above; in this case, the parental investment is simply how many resources can be invested in each offspring before they are born. Reproductive Events per Lifetime The trade-off between age and fecundity plays a key role in many life histories. Annual plants and mos...
ending the high costs of reproduction. In long-lived animals, the relative advantage of juvenile experience outweighs the energy investment in survival and growth. In shorter-lived animals, on the other hand, quick reproduction is more critical than juvenile training, and reproduction tends to occur earlier. Life histo...
10 years, their descendants would form a swarm more than 2 meters thick over the entire surface of the earth! In practice, such patterns of unrestrained growth prevail only for short periods, usually when an organism reaches a new habitat with abundant resources (figure 24.16). Natural examples include dandelions reac...
by N, the number of individuals present at any one time), adjusted for the amount of resources available. The adjustment is made by multiplying rN by the fraction of K still unused (K minus N, divided by K). As N increases (the population grows in size), the fraction by which r is multiplied (the remaining resources) ...
are density-dependent. When populations approach their carrying capacity, competition for resources can be severe, leading both to a decreased birthrate and an increased risk of mortality (figure 24.18). In addition, predators often focus their attention on particularly common prey, which also results in increasing ra...
many cases, such patterns result because growth is under the control of density-independent effects. In other words, the rate of growth of a population at any instant is limited by something other than the size of the population. 0 A variety of factors may affect populations in a density-independent manner. Most of th...
Year FIGURE 24.20 Linked population cycles of the snowshoe hare and the northern lynx. These data are based on records of fur returns from trappers in the Hudson Bay region of Canada. The lynx populations carefully track the snowshoe hares, but lag behind them slightly. Which factor is responsible for the predator-pre...
& Row, New York. Population Growth Rates and Life History Models As we have seen, some species usually have stable population sizes maintained near the carrying capacity, whereas the populations of other species fluctuate markedly and are often far below carrying capacity. As we saw in our discussion of life histories...
selected life history traits, including small brood size, late reproduction, and a high degree of parental care. These life history traits evolved during the early history of hominids, when the limited resources available from the environment controlled population size. Throughout most of human history, our populations...
24.22 History of human population size. Temporary increases in death rate, even severe ones like the Black Death of the 1400s, have little lasting impact. Explosive growth began with the Industrial Revolution in the 1700s, which produced a significant long-term lowering of the death rate. The current population is 6 b...
44 years old represent the “baby boom.” The rectangular shape of the population pyramid indicates that the population of the United States is not expanding rapidly. The very triangular pyramid of Kenya, by contrast, predicts explosive future growth. The population of Kenya is predicted to double in less than 20 years....
the fraction of the world’s population that lives in industrialized countries. In 1950, fully onethird of the world’s population lived in industrialized countries; by 1996 that proportion had fallen to one-quarter; in 2020 the proportion will have fallen to one-sixth. Thus the world’s population growth will be centere...
dichotomy, significant efforts are underway worldwide to lower birthrates. The human population has been growing rapidly for 300 years, since technological innovations dramatically reduced the death rate. Chapter 24 Population Ecology 513 Chapter 24 Summary www.mhhe.com/raven6e www.biocourse.com Questions Media Resour...
What is the definition for the actual rate of population increase? What other two factors affect it? 7. What is an exponential capacity for growth? When does this type of growth naturally occur? Give an example. 8. What is carrying capacity? Is this a static or dynamic measure? Why? 9. What is the difference between r...
urbance. Disturbances can disrupt successional change. In some cases, moderate amounts of disturbance increase species diversity. FIGURE 25.1 Communities involve interactions between disparate groups. This clownfish is one of the few species that can nestle safely among the stinging tentacles of the sea anemone—a class...
Semibalanus balanoides (called Balanus balanoides prior to 1995) lives lower down, where it is rarely exposed to the atmosphere (figure 25.2). In the deeper zone, Semibalanus could always outcompete Chthamalus by crowding it off the rocks, undercutting it, and replacing it even where it had begun to grow, an example o...
A niche may be defined as the way in which an organism utilizes its environment. Interspecific interactions may cause a species’ realized niche to be smaller than its fundamental niche. If resources are limiting, two species normally cannot occupy the same niche indefinitely. Gause and the Principle of Competitive Exc...
, both species were able to survive. However, competition did have a negative effect on the participants (figure 25.3c). When grown without a competitor, both species reached densities three times greater than when they were grown with a competitor. Competitive Exclusion Gause’s principle of competitive exclusion can b...
• • 0 4 12 8 Days 16 20 24 75 50 25 0 (c) •• • •• • 0 4 • • P. caudatum P. bursaria •• • • • •• • • • • • • • •• •• • •• • • • • 8 12 16 20 Days Chapter 25 Community Ecology 517 Resource Partitioning Gause’s exclusion principle has a very important consequence: persistent competition between two species is rare in nat...
bills of similar size when allopatric, but different size when sympatric. populations. Called character displacement, the differences evident between sympatric species are thought to have been favored by natural selection as a mechanism to facilitate habitat partitioning and thus reduce competition. Thus, the two Darw...
of North America. In 1988, researchers set up a series of 50 meter 50 meter enclosures to investigate the effect of kangaroo rats on other, smaller seed-eating rodents. Kangaroo rats were removed from half of the enclosures, but not from the other enclosures. The walls of all of the enclosures had holes in them that a...
of each species will prey on juveniles of the other species. In addition, the presence of one species may attract predators, which then also prey on the second species. In this case, the second species may have a lower population size in the presence of the first species due to the presence of predators, even if they ...
populations exploded. Conversely, the introduction of rats, dogs, and cats to many islands around the world has led to the decimation of native faunas. Populations of Galápagos tortoises on several islands are endangered, for example, by introduced rats, dogs, and cats, which eat eggs and young tortoises. Similarly, s...
to be able to grasp. In turn, these adaptations may have pressured predators to evolve ever more effective predatory adaptations and tactics. Predation and Evolution Predation provides strong selective pressures on prey populations. Any feature that would decrease the probability of Predation can have substantial effe...
from eating them. In addition, these plants usually contain cardiac glycosides, molecules named for their drastic effect on heart function in vertebrates. The Evolutionary Response of Herbivores Certain groups of herbivores are associated with each family or group of plants protected by a particular kind of secondary ...
the chrysalis stage to the adult and even to the eggs of the next generation. The incorporation of cardiac glycosides thus protects all stages of the monarch life cycle from predators. A bird that eats a monarch butterfly quickly regurgitates it (figure 25.9) and in the future avoids the conspicuous orange-and-black p...
probably avoid trying to capture all orange-and-black insects in the future. FIGURE 25.10 Cryptic coloration. An inchworm caterpillar (Necophora quernaria) (hanging from the upper twig) closely resembles a twig. FIGURE 25.11 Vertebrate chemical defenses. Frogs of the family Dendrobatidae, abundant in the forests of La...
ars feed on willows and cottonwoods, and neither caterpillars nor adults were thought to be distasteful to birds, although recent findings may dispute this. Interestingly, the Batesian mimicry seen in the adult viceroy butterfly does not extend to the caterpillars: viceroy caterpillars are camouflaged on leaves, resemb...
ps they mimic, flying often and actively from place to place. In Batesian mimicry, unprotected species resemble others that are distasteful. Both species exhibit aposematic coloration. In Müllerian mimicry, two or more unrelated but protected species resemble one another, thus achieving a kind of group defense. Chapter...
spores of particular fungi. These fungi are cultivated by the ants and brought from one specially prepared bed to another, where they grow and reproduce. In turn, the fungi constitute the primary food of the ants and their larvae. The relationship between leafcutter ants and these fungi is an excellent example of symb...
anemones secrete different chemical mediators; these attract particular species of fishes and may be toxic to the fish species that occur symbiotically with other species of anemones in the same habitat. There are 26 species of clownfishes, all found only in association with sea anemones; 10 species of anemones are in...
Mutualism is a symbiotic relationship among organisms in which both species benefit. Examples of mutualism are of fundamental importance in determining the structure of biological communities. Some of the most spectacular examples of mutualism occur among flowering plants and their animal visitors, including insects, ...
provide a balanced diet, including the sugar-rich nectar and the protein-rich Beltian bodies. What, if anything, do the ants do for the plants? Whenever any herbivore lands on the branches or leaves of an acacia inhabited by ants, the ants, which continually patrol the acacia’s branches, immediately attack and devour ...
, or parasite, is much smaller than the prey and remains closely associated with it. Parasitism is harmful to the prey organism and beneficial to the parasite. The concept of parasitism seems obvious, but individual instances are often surprisingly difficult to distinguish from predation and from other kinds of symbios...
a parasite and has lost its chlorophyll and its leaves in the course of its evolution. Because it is heterotrophic, unable to manufacture its own food, dodder obtains its food from the host plants it grows on. FIGURE 25.17 Brood parasitism. This bird is feeding a cuckoo chick in its nest. The cuckoo chick is larger th...
major predator such as wolves or mountain lions from a community. The result is to decrease rather than increase the biological diversity of the community, the opposite of what is intended. Parasitism May Counter Competition Parasites may effect sympatric species differently and thus influence the outcome of interspec...
of removing a competitor; why did it reverse? The answer reveals the intricacies of natural ecosystems (figure 25.20). Rodents prefer large seeds, whereas ants prefer smaller seeds. Further, in this system plants with large seeds are competitively superior to plants with small seeds. Thus, the removal of rodents leads...
have a tendency to change from simple to complex in a process known as succession. This process is familiar to anyone who has seen a vacant lot or cleared woods slowly become occupied by an increasing number of plants, or a pond become dry land as it is filled with vegetation encroaching from the sides. Succession If ...
in it in ways that favor other species. 530 Part VII Ecology and Behavior 300 250 200 150 100 50 Nitrogen in forest floor b Nitrogen in mineral soil Year 1 Year 100 Year 200 Pioneer mosses Invading alders Alder thickets Spruce forest FIGURE 25.22 Plant succession produces progressive changes in the soil. Initially, th...
ets. As soil nitrogen levels rise, (c) spruce crowd out the mature alders, forming a forest. The Role of Disturbance Disturbances often interrupt the succession of plant communities. Depending on the magnitude of the disturbance, communities may revert to earlier stages of succession or even, in extreme cases, begin at...
ably move along a successional trajectory culminating in the development of a climax community is no longer widely accepted. Rather, predicting the state of a community in the future may be difficult because the unpredictable occurrence of disturbances will often counter successional changes. Understanding the role tha...
. Which would be associated with an adult viceroy butterfly? Which would be associated with a larval monarch butterfly? Which would be associated with a larval viceroy butterfly? 5. Why is eliminating predators a bad idea for species richness? 6. How can predation and competition interact in regulating species diversit...
will survive into adulthood. Organisms interact with their environment in many ways. To understand these interactions, we need to appreciate both the internal factors that shape the way an animal behaves, as well as aspects of the external environment that affect individuals and organisms. In this chapter, we explore ...
could also ask why the behavior evolved, that is, what is its adaptive value? This is a question concerning ultimate causation. To study the ultimate cause of a behavior, we would attempt to determine how it influenced the animal’s survival or reproductive success. Thus, a male songbird may sing during the breeding se...
goose completes the behavior, as if driven by a program released by the initial sight of the egg outside the nest. According to ethologists, egg retrieval behavior is triggered by a sign stimulus (also called a key stimulus), the appearance of an egg out of the nest; a component of the goose’s nervous system, the inna...
responsible for the transduction of visual stimuli. Rhodopsin is made of cis-retinal and the protein opsin. Light is absorbed by the visual pigment cis-retinal causing it FIGURE 26.3 Lizard prey capture. The complex series of movements of the tongue this chameleon uses to capture an insect represents a fixed action pa...
. roseicollis carries material tucked under its flank feathers (figure 26.5). When Dilger crossed the two species to produce hybrids, he found that the hybrids carry nest material in a way that seems intermediate between that of the parents: they repeatedly shift material between the bill and the flank feathers. Other ...
a nursing posture over offspring. (d) Proportion of pups retrieved when they were experimentally moved. (a) (bc 14 12 10 8 6 4 2 0 1.0 0.8 0.6 0.4 0.2 (d) fosB alleles present fosB alleles absent Single Gene Effects on Behavior The maze-learning, hybrid, and identical twins studies just described suggest genes play a ...
amus. These modifications within the brain cause the female to react maternally toward her offspring. In contrast, in mothers lacking the fosB alleles, this reaction is stopped midway. No protein is activated, the brain’s neural circuitry is not rewired, and maternal behavior does not result. As these genetic technique...
sensitization. The two major types of associative learning are called classical conditioning and operant conditioning; they differ in the way the associations are established. Classical Conditioning In classical conditioning, the paired presentation of two different kinds of stimuli causes the animal to form an associ...
Today, it is thought that instinct guides learning by determining what type of information can be learned through conditioning. Instinct It is now clear that some animals have innate predispositions toward forming certain associations. For example, if a rat is offered a food pellet at the same time it is exposed to X ...
between stimuli and responses. In contrast, associative learning (classical and operant conditioning) involves the formation of an association between two stimuli or between a stimulus and a response. Chapter 26 Animal Behavior 539 The Development of Behavior Behavioral biologists now recognize that behavior has both ...
lings following Konrad Lorenz think he is their mother. He is the first object they saw when they hatched, and they have used him as a model for imprinting. (a) (b) FIGURE 26.10 How imprinting is studied. Ducklings will imprint on the first object they see, even (a) a black box or (b) a white sphere. childhood and adul...
a fully developed, white-crowned sparrow song as adults. These results suggest that these birds have a genetic template, or instinctive program, that guides them to learn the appropriate song. During a critical period in development, the template will accept the correct song as a model. Thus, song acquisition depends ...
arrows that heard no song during rearing. This difference indicates that the genetic program itself is insufficient to produce a normal song. FIGURE 26.12 Brood parasite. Cuckoos lay their eggs in the nests of other species of birds. Because the young cuckoos (large bird to the right) are raised by a different species ...
by testosterone and related steroid hormones. The male’s behavior causes the release of FSH in the female, and FSH promotes the growth of the ovarian follicles (see chapter 59). The developing follicles release estrogens, which affect other reproductive tissues. Nest construction follows after one or two days. The pre...
be in part responsible for the “mood swings” experienced by some human females during the menstrual cycle. Hormones have important influences on reproductive and social behavior. Behavioral Rhythms Many animals exhibit behaviors that vary at regular intervals of time. Geese migrate south in the fall, birds sing in the...
, most of these people adopt daily activity patterns (one phase of activity plus one phase of sleep) of about 25 hours, although there is considerable variation. Some individuals exhibit 50-hour clocks, active for as long as 36 hours during each period! Under normal circumstances, the day-night cycle resets an individu...
-running cycle periods of approximately 24 hours; they are entrained to a more exact 24-hour cycle period by environmental cues. Chapter 26 Animal Behavior 543 26.3 Communication is a key element of many animal behaviors. Much of the research in animal behavior is devoted to analyzing the nature of communication signal...
to female and then leads her to nest 3 Male shows female entrance to nest 4 Female enters nest and spawns while male stimulates tail 5 Male enters nest and fertilizes eggs FIGURE 26.15 A stimulus-response chain. Stickleback courtship involves a sequence of behaviors leading to the fertilization of eggs. 544 Part VII E...
been determined. Each male then “knows” his neighbor by the song he sings, and also “knows” that male does not constitute a threat because they have already settled their territorial contests. So, all birds in the population can lower their energy costs by identifying their neighbors through their individualistic song...
from the hive, collecting nectar and pollen from a variety of plants and switching between plant species and populations on the basis of how energetically rewarding their food is. The food sources used by bees tend to occur in patches, and each patch offers much more food than a single bee can transport to the hive. A...
.5 seconds Eagle 0.5 seconds Leopard b) (a) FIGURE 26.20 Primate semantics. (a) Predators, like this leopard, attack and feed on vervet monkeys. (b) The monkeys give different alarm calls when eagles, leopards, and snakes are sighted by troupe members. Each distinctive call elicits a different and adaptive escape behav...
. That is why English speakers have difficulty mastering the throaty French “r,” French speakers typically replace the English “th” with “z,” and native Japanese often substitute “l” for the unfamiliar English “r.” Children go through a “babbling” phase, in which they learn by trial and error how to make the sounds of ...
their summer breeding ranges. What is amazing about the migration of the monarch, however, is that two to five generations may be produced as the butterflies fly north. The butterflies that migrate in the autumn to the precisely located overwintering grounds in Mexico have never been there before. When colonies of bob...
established range in the Midwest. When they migrate to South America in the winter, bobolinks that nested in the West do not fly directly to the winter range; instead, they fly to the Midwest first and then use the ancestral flyway. (b) The golden plover has an even longer migration route that is circular. These birds...
Spain FIGURE 26.23 Migratory behavior of starlings. The navigational abilities of inexperienced birds differ from those of adults who have made the migratory journey before. Starlings were captured in Holland, halfway along their full migratory route from Baltic breeding grounds to wintering grounds in the British Isl...
of their troop. There are many anecdotal accounts that appear to support the idea that deception occurs in some nonhuman primate species such as baboons and chimpanzees, but it has been difficult to devise fieldbased experiments to test this idea. Much of this type of research on animal cognition is in its infancy, bu...
never seen string before and were unable to get at the meat. After several hours, during which time the birds periodically looked at the meat but did nothing else, one bird flew to the branch, reached down, grabbed the string, pulled it up, and placed it under his foot. He then reached down and grabbed another piece o...
sexual imprinting? Why do some young animals imprint on objects like a moving box? 4. How does Marler’s work on song development in whitecrowned sparrows indicate that behavior is shaped by learning? How does it indicate that behavior is shaped by instinct? 26.3 Communication is a key element of many animal behaviors....
tebrate Societies. Many vertebrate societies exhibit altruism. Human Sociobiology. Human behavior, like that of other vertebrates, is influenced by natural selection. FIGURE 27.1 A snake in the throes of death—or is it? When threatened, many organisms feign death, as this snake is doing—foaming at the mouth and going l...
and reproduction. Current research in behavioral ecology focuses on the contribution behavior makes to an animal’s reproductive success, or fitness. As we saw in chapter 26, differences in behavior among individuals often result from genetic differences. Thus, natural selection operating on behavior has the potential ...

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