CONCEPTS IN BIOLOGY

PART IV. EVOLUTION AND ECOLOGY

18. Evolutionary and Ecological Aspects of Behavior

18.7. Selected Topics in Behavioral Ecology

The science of animal behavior is a broad one, drawing on information from several fields of study, and it can be used to explore many kinds of questions. Of the examples so far in this chapter, some involved laboratory studies, some were field studies, and some included aspects of both. Often, these studies overlap with the field of psychology. This is particularly true for many of the laboratory studies. The topics that follow concentrate on the significance of behavior from ecological and evolutionary points of view. Now that we have some understanding of how organisms generate behavior, we can look at a variety of behaviors in several kinds of animals and see how they are significant for their ecological niches.

Communication

Communication is the use of signals to convey information from one animal to another. Animals communicate in many ways and for a variety of purposes.

Sensory Systems

The senses of hearing, sight, taste, smell, and touch are all involved in communication. Regardless of the sensory system used, communication involves the production of signals that can be received and interpreted by others of the same species. For most animals, the communication system is instinctive. However, in humans language is a learned behavior.

1. Sound is used by many kinds of animals for communication. Birds, frogs, alligators, crickets, wolves, and many other animals use sound to communicate information.

2. Sight is used to communicate in many ways. Colors, lights, body postures, and movements are all involved in communication.

3. The chemical senses of taste and smell are important in the communication system of many kinds of animals. Pheromones are chemicals produced by animals and released into the environment that trigger behavioral or developmental changes in other animals of the same species. For example, honeybees produce a pheromone that smells like bananas to humans. This pheromone triggers aggressive behavior in the bees of the hive. Many kinds of animals produce odors that communicate information about their reproductive status. Licking or touching with antennae is a way to obtain chemical information about other animals.

4. Touch is probably involved in the communication systems of nearly all organisms. If nothing else, the touch of one animal by another announces its presence.

Often, several of the senses are used at the same time in the process of communication. For example, when two dogs meet for the first time, they are likely to communicate by sound, sight, smell, touch, and taste. They bark or growl. They assume special body postures or bare their teeth, which are visual signals. They sniff one another. They may push one another, or one may put a leg over the other’s body. Finally, if they are friendly, they are likely to lick one another.

Purposes of Communication

Animals communicate for several purposes.

1. Advertising location is an important function of communication. Information about location can be used to gather individuals together. The calls of frogs in the spring bring animals together at a breeding site (figure 18.12). The calls of crows can call attention to a predator or food source. Many birds use sounds to attract potential mates to their location. The same sounds can be used to tell others of the same species that a particular piece of the habitat is occupied and to stay away.

FIGURE 18.12. Communication by Sound

This tree frog is calling. The inflated vocal sac amplifies the sound he produces.

2. Social structure among animals that live in groups is maintained through communication. The elaborate greeting activities of wolves are an example. There is much posturing, touching, smelling, licking, and vocalization, all of which help reinforce the status of each individual in the group (figure 18.13).

FIGURE 18.13. Maintaining Social Order

Many kinds of body postures and actions are used for communication that reinforces the social status of animals. The wolf on the left is the dominant wolf. It has its ears up, head in an elevated position, and is staring. The wolf on the right is in a submissive position. Its ears are back and its head is lowered. Both wolves are showing aggression with exposed teeth.

3. Alarm signals alert animals to potential danger. The alarm pheromone of honeybees mentioned earlier is an example. The raised tail of a white-tailed deer is a similar signal, but deer also snort and stamp their forefeet when they are disturbed by something in their surroundings.

And many birds and mammals use alarm calls to alert others to the presence of danger.

4. Reproduction requires communication. Information about the location and reproductive readiness of individuals is important for reproduction to be successful.

Reproductive Behavior

The reproductive behavior of many kinds of animals has been studied a great deal. Although each species has its own behaviors, some components of reproductive behavior are common to nearly all animals. In order for an animal to produce offspring that reach adulthood, several events must occur. A suitable mate must be located, mating and fertilization must take place, and the young must be provided for.

Finding Each Other

To reproduce, an animal must find individuals of the same species that are of the opposite sex. Various species use different methods, but most send signals that can be interpreted by others of the same species. Depending on the species, any of the senses (sound, sight, touch, smell, or taste) may be used to identify the species, sex, and sexual receptiveness of another animal. For instance, different species of frogs produce distinct calls. The call produced by male frogs, which both male and female frogs can hear, results in frogs of both sexes congregating in a limited area. Once they gather in a small pond, it is much easier to have the further communication necessary for mating to take place. Many other animals, including most birds, insects (e.g., crickets), reptiles (e.g., alligators), and some mammals, produce sounds that are important for bringing individuals together for mating.

Chemicals can have the same effect as the sounds made by frogs or birds; they are just a different code system. For example, many kinds of female moths release a chemical into the air. The large, fuzzy antennae of the male moths can receive the chemical in unbelievably tiny amounts. The males fly upwind to the source of the pheromone, which is a female (figure 18.14).

FIGURE 18.14. Chemical Communication

The female moth signals her readiness to mate and attracts males by releasing a pheromone, which attracts males from long distances downwind.

Most mammals rely on odors. Females typically produce distinct odors when they are in breeding condition. When a male happens on such an odor trail, he follows it to the female. Many reptiles also produce distinctive odors that are attractants.

Visual cues are also important for many species. Brightly colored birds, insects, fish, and many other animals use specific patches of color for species identification. Conspicuous movements can also be used to attract the attention of a member of the opposite sex.

The firefly is probably the most familiar organism that uses light signals to bring males and females together. Several species may live in the same area, but each species flashes its own code. The code is based on the length of the flashes, their frequency, and their overall pattern (figure 18.15). There is also a difference between the signals given by males and those given by females. For the most part, males are attracted to and mate with females of their own species. Once male and female animals have attracted one another’s attention, the second stage in successful reproduction takes place. However, in one species of firefly, the female has the remarkable ability to signal the correct answering code to species other than her own. After she has mated with a male of her own species, she continues to signal to passing males of other species. She is not hungry for sex, just hungry. The luckless male who responds to her “come-on” will be her dinner.

FIGURE 18.15. Firefly Communication

The pattern of light flashes, their location, and their duration all help fireflies identify members of the opposite sex who are of the appropriate species.

Courtesy of James E. Lloyd.

Assuring Fertilization

The second important activity in reproduction is fertilizing eggs. Many marine organisms simply release their gametes into the sea simultaneously and allow fertilization and further development to take place without any input from the parents. Sponges, jellyfishes, and many other marine animals fit into this category. Other aquatic animals congregate, so that the chances of fertilization are enhanced by the male and female being near one another as the gametes are shed. This is typical of many fish and some amphibians, such as frogs. Internal fertilization, in which the sperm are introduced into the female’s reproductive tract, occurs in most terrestrial animals. Some spiders and other terrestrial animals produce packages of sperm, which the female picks up with her reproductive structures. Many of these mating behaviors require elaborate, species-specific communication prior to the mating act.

Raising Young

The third element in successful reproduction is providing the young with the resources they need to live to adulthood. Many invertebrate animals spend little energy on the care of the young, leaving them to develop on their own. Usually, the young become free-living larvae, which eat and grow rapidly. Many insects lay their eggs on the particular species of plant that the larva will feed on as it develops. Parasitic species seek out the required host in which to lay their eggs. The eggs of others may be placed in spots that provide safety until the young hatch from the egg (figure 18.16). Turtles, many fish, and some insects fit into this category. In most of these cases, however, the female lays large numbers of eggs, and most of the young die before reaching adulthood. This is an enormously expensive process: The female invests considerable energy in producing eggs but has a low success rate. Nevertheless, most species use this strategy, and it has proven to be very successful.

FIGURE 18.16. No Parental Care

The mother of these caterpillars does not provide any care for her offspring. The only provision she has made for her offspring is to lay her eggs on a suitable food plant. Most of these larvae will die.

An alternative strategy to this “wasteful” loss of potential young is to produce fewer young but invest large amounts of energy in their care. This is not necessarily a more efficient system, because it still requires large investments by the parents in the production and care of the young. This strategy is typical of birds and mammals. Parents build nests, share in the feeding and protection of the young, and often assist the young in learning appropriate behaviors. Caring for the young requires many complex behavior patterns (figure 18.17). Most of the animals that feed and raise young are able to distinguish their own young from those of other nearby families and may even kill the young of another family unit. Elaborate greeting ceremonies are usually performed when animals return to the nest or the den. Perhaps this has something to do with being able to identify individual young. Often, this behavior is shared among adults as well. This is true for many colonial nesting birds, such as gulls and penguins, and for many carnivorous mammals, such as wolves, dogs, and hyenas.

FIGURE 18.17. Parental Care

Mammals and birds typically invest a great deal of energy in caring for their young. (a) Zebras protect their young and provide food in the form of milk. (b) Robins and other birds build nests away from most predators, and provide food until the young are able to fend for themselves.

Care of the young also occurs in several species of fish and reptiles, such as alligators. Certain kinds of insects, such as bees, ants, and termites, have elaborate social organizations in which one or a few females (queens) produce large numbers of young, which are cared for by the queen’s sterile offspring. Most of the offspring are sterile workers, but a few become new queens.

Territorial Behavior

A territory is the space used for food, mating, or other purposes, that an animal defends against others of the same species. Territorial behaviors are activities performed to secure and defend a space. These behaviors are widespread in the animal kingdom and can be seen in such diverse groups as insects, spiders, fish, reptiles, birds, and mammals (figure 18.18). On the other hand, many kinds of animals do not establish fixed territories. For example, most insects, worms, and many other invertebrates do not form territories. In addition, many kinds of migratory animals, such as tuna and wildebeest, do not establish territories or do so only during the breeding season.

FIGURE 18.18. Territorial Behavior

This clown fish lives with a sea anemone. It will defend its small territory against other clown fish.

Territorial Behavior Reduces Conflict

When territories are first being established, there is often much conflict among individuals. However, this eventually gives way to their use of signals that define the territory and communicate to others that the territory is occupied. For example, the male redwing blackbird has red shoulder patches, but the female does not. The male will perch on a high spot, flash his red shoulder patches, and sing to other males that venture into his territory. Most other males get the message and leave his territory; those that do not leave are attacked. He will also attack other red objects such as people wearing red caps. Clearly, the spot of red is the characteristic that stimulates the male to defend his territory. Once the initial period of conflict is over, the birds tend to respect one another’s boundaries. All that is required is to frequently announce that the territory is still occupied. They do so by singing from a conspicuous position in the territory. After territorial boundaries have been established, little time is required to prevent other males from venturing close. Thus, the animal may spend a great deal of time and energy securing the territory initially, but doesn’t need to expend much to maintain it.

Territorial Behavior Involves Special Signals

For redwing blackbirds, singing in a conspicuous location and flashing red shoulder patches is a signal warning other male blackbirds to stay away. The use of signals replaces the need for fighting. Much of the singing behavior of other species of birds is also territorial. Many carnivorous mammals, such as foxes, weasels, cougars, coyotes, and wolves, use urine or other scents to mark the boundaries of their territories. Territorial fish use color patterns and threat postures to defend their territories. Crickets use sound and threat postures. Male bullfrogs engage in shoving matches to displace males that invade their small territories along the shoreline.

Territorial Behavior Allocates Resources

A territory has great importance, because it reserves exclusive rights to the use of a certain space for an individual or small group of individuals, such as a pair of robins or a wolf pack. These resources may include sources of food or water, nest or den sites, or access to potential mates. Thus, establishing and maintaining a territory is a way to allocate resources among the members of a species. This is also likely to have an effect on population size, because animals that are not able to establish a territory or are forced to accept poor-quality territories will be less likely to survive and reproduce.

Territory Size

Different species of animals maintain territories for different purposes. Some species maintain small territories of a few square meters, whereas others maintain territories of several square kilometers. For example, many seabirds build nests in colonies. Each pair of birds maintains an extremely small nesting territory of about 1 square meter within the colony. Each territory is just beyond the reach of the bills of the neighbors (figure 18.19). When one bird invades the nesting territory of another, the resident bird uses threat postures to drive the intruder away. If the intruder does not take the hint, it is attacked. Many kinds of fish also maintain small territories.

FIGURE 18.19. Territory Size

Colonial nesting seabirds typically have very small nest territories. Each territory is just out of pecking range of the neighbors.

Many other birds maintain territories for both nesting and gathering food resources. These territories range from a few hundred square meters, such as for robins, to several square kilometers, such as for owls.

Many large carnivores have territories that cover several square kilometers. In such cases, the signals they use must be perceived over great distances or last for a long time. The howling of wolves and the roaring of lions are signals that can be heard over long distances (figure 18.20). The use of scent posts—places where animals urinate, defecate, or deposit other scents, transmits long-lasting signals. The “owner” of the territory does not need to be present all the time to defend its territory, but it must visit these sites regularly to renew the signal.

FIGURE 18.20. Advertising One's Territory

The howling of this wolf has several functions. One is to advertise its presence in its territory.

Dominance Hierarchy

In social animals, a kind of organization known as a dominance hierarchy is often observed. A dominance hierarchy is a relatively stable, mutually understood order of priority within the group. One individual in the group dominates all the others. A second-ranking individual dominates all but the highest-ranking individual, and so forth; the lowest- ranking individual must give way to all others within the group. Generally, the initial establishment of a dominance hierarchy involves fighting. The best fighters take the top places. However, once the hierarchy is established, it results in a more stable social unit with little conflict, because the positions of the individuals within the hierarchy are reinforced by various kinds of threats without the need for fighting. This kind of behavior is seen in barnyard chickens and is known as a pecking order. Figure 18.21 shows a dominance hierarchy; the lead animal has the highest rank and the last animal has the lowest rank.

A dominance hierarchy gives certain individuals preferential treatment when resources are scarce. The dominant individual has first choice of food, mates, shelter, water, and other resources because of its position. Animals low in the hierarchy may be malnourished or fail to mate in times of scarcity. In many social animals, such as wolves, usually only the dominant male and female reproduce. If the dominant male and female have achieved their status because they have superior characteristics, their favorable genes will probably be passed on to the next generation. Poorly adapted animals with low rank may never reproduce. Such a hierarchy frequently results in low-ranking individuals emigrating from the area. Such migrating individuals are often subject to heavy predation.

FIGURE 18.21. A Dominance Hierarchy

Many animals maintain order within their groups by establishing a dominance hierarchy. For example, in a group of cows or sheep walking in single file, the dominant animal is probably at the head of the line and the lowest-ranking individual is at the end.

Behavioral Adaptations to Seasonal Changes

Most animals live in environments that change from time to time. There may be differences in temperature, rainfall, or availability of food. In some areas, the dry part of the year is the most stressful. In temperate areas, winter reduces many sources of food and forces organisms to adjust. Animals have several behavioral means for coping with these changes.

1. Metabolic changes allow many animals to avoid seasonal changes or times of environmental stress. Where drought occurs, many animals become inactive until water becomes available. Frogs, toads, and many insects remain inactive (estivate) underground during long periods of drought and emerge to mate when it rains. Hibernation in mammals is a response to cold, seasonal temperatures in which the body temperature drops and all the body processes slow down. The slowing of body processes allows an animal to survive on the food it has stored within its body as fat prior to the onset of severe environmental conditions and low food availability. Hibernation is typical of bats, marmots, and some squirrels. Animals such as insects, reptiles, and amphibians are not able to regulate their temperatures the way birds and mammals do. Because their body temperatures drop when the environmental temperature drops, their activities are slowed during the winter and they require less food.

2. Migration allows many animals simply to move to areas that are less stressful. Migratory birds fly hundreds or thousands of kilometers. Many birds that nest in the north avoid winter by migrating to more southerly regions (figure 18.22). Many migratory mammals move from drier areas where food has been depleted to other moister areas where food is more available. In many cases, the migrations are triggered by instinctive responses to environmental clues, and the same migration routes are used generation after generation.

FIGURE 18.22. Seasonal Migration

(a) Snow geese and many other birds migrate from their northern breeding grounds to milder climates during the winter. In this way, they are able to use the north for breeding and avoid the harsh winter climate. (b) Wildebeest migrate annually to find better grazing.

3. Storing food during seasons of plenty for periods of scarcity is a common behavior pattern. These behaviors are instinctive and are seen in a variety of animals. Squirrels bury nuts, acorns, and other seeds. (They also plant trees because they never find all the seeds they bury.) Chickadees stash seeds in cracks and crevices when food is plentiful and spend many hours during the winter exploring similar places for food. Some of the food they find is food they stored. Honeybees store honey, which allows them to live through the winter when nectar is not available. This requires a rather complicated set of behaviors that coordinates the activities of thousands of bees in the hive.

Navigation and Migration

Because animals move from place to place to meet their needs, it is useful for them to be able to return to a nest, water hole, den, or favorite feeding spot. This requires some memory of their surroundings (a mental map) and a way of determining direction. Direction can be determined by such things as magnetic fields, landmarks, scent trails, or reference to the Sun or stars. If the Sun or stars are used for navigation, some sort of time sense is also needed because these bodies move in the sky. It is valuable to have information about distance as well.

Animals often use the ability to sense changes in time to prepare for seasonal changes. Away from the equator, the length of the day—the photoperiod—changes as the seasons change. Many birds prepare for migration and have their migration direction determined by the changing photoperiod. For example, in the fall, many birds instinctively change their behavior, store up fat, and begin to migrate from northern areas to areas closer to the equator. This seasonal migration allows them to avoid the harsh winter conditions signaled by the shortening of days. The return migration in the spring is triggered by the lengthening photoperiod. This migration requires a lot of energy, but it allows many birds to exploit temporary food resources in the north during the summer months.

In honeybees, navigation also involves communication among the various individuals that are foraging for nectar. The bees are able to communicate information about the direction and distance of the nectar source from the hive. If the source of nectar is some distance from the hive, the scout bee performs a “wagging dance” in the hive. The bee walks in a straight line for a short distance, wagging its rear end from side to side. It then circles around back to its starting position and walks the same path as before (figure 18.23). This dance is repeated many times. The direction of the straight-path portion of the dance indicates the direction of the nectar relative to the position of the Sun. For instance, if the bee walks straight upward on a vertical surface in the hive, this tells the other bees to fly directly toward the Sun. If the path is 30° to the left of vertical, the source of the nectar is 30° to the left of the Sun’s position.

FIGURE 18.23. Honeybee Communication and Navigation

The direction of the straight, tail-wagging part of the dance of the honeybee indicates the direction to a source of food. The angle that this straight run makes with the vertical is the same angle the bee must fly in relation to the Sun to find the food source. The length of the straight run and the duration of each dance cycle indicate the flying time necessary to reach the food source.

The duration of the entire dance and the number of waggles in its straight-path portion are positively correlated with the length of time the bee must fly to get to the nectar source. So the dance communicates the duration of flight as well as the direction. Because the recruited bees have picked up the scent of the nectar source from the dancer, they also have information about the kind of flower to visit when they arrive at the correct spot. Because the Sun is not stationary in the sky, the bee must constantly adjust its angle to the Sun. It appears that they do this with an internal clock. Bees that are prevented from going to the source of nectar or from seeing the Sun still fly in the proper direction sometime later, even though the position of the Sun is different.

Like honeybees, some daytime-migrating birds use the Sun to guide them. For nighttime migration, some birds use the stars to help them find their way. In one interesting experiment, warblers, which migrate at night, were placed in a planetarium. The pattern of stars as they appear at any season could be projected onto a large, domed ceiling. In autumn, when these birds would normally migrate southward, the stars of the autumn sky were shown on the ceiling. The birds responded with much fluttering activity at the south side of the cage, as if trying to migrate southward. Then, the experimenters projected the stars of the spring sky, even though it was autumn. The birds then attempted to fly northward, although there was less unity in their efforts to head north; the birds seemed somewhat confused. Nevertheless, the experiment showed that the birds recognized star patterns and were influenced by them.

Some birds navigate by compass direction—that is, they fly as if they had a compass in their heads. They seem to be able to sense magnetic north. Their ability to sense magnetic fields was proven at the U.S. Navy’s test facility in Wisconsin. The weak magnetism radiated from this test site has changed the flight patterns of migrating birds, but it is yet to be proved that birds use the Earth’s magnetism to guide their migration. Homing pigeons are famous for their ability to find their way home. They make use of a wide variety of clues, but it has been shown that one of the clues they use is magnetism. In one study, birds with tiny magnets glued to the sides of their heads were very poor navigators; others, with nonmagnetic objects attached to the sides of their heads, did not lose their ability to navigate.

Social Behavior

A society is a group of animals of the same species that interact with one another and in which there is a division of labor.

Animal societies exhibit many levels of complexity, and the types of social organization differ from species to species. Some societies show little specialization of individuals other than that determined by sexual differences and differences in physical size and endurance. The African wild dog illustrates such a flexible social organization. These animals are nomadic and hunt in packs. Although an individual wild dog can kill prey about its own size, groups are able to kill fairly large animals if they cooperate in the chase and kill. Young pups are unable to follow the pack. When adults return from a successful hunt, they regurgitate food if the proper begging signal is presented to them (figure 18.24). Therefore, the young and the adults that remained behind to guard the young are fed by the returning hunters. The young are the responsibility of the entire pack, which cooperates in their feeding and protection. While the young are at the den site, the pack must give up its nomadic way of life. Therefore, the young are born during the time of year when prey are most abundant. Only the dominant female in the pack has young each year. If every female had young, the pack couldn’t feed them all. At about 2 months of age, the young begin to travel with the pack, and it can return to its nomadic way of life.

FIGURE 18.24. African Wild Dog Society

African wild dogs hunt in groups and share food, which they take back to the den. Only the dominant male and female mate and raise offspring.

Honeybees have a social organization with a high degree of specialization. A hive may contain thousands of individuals, but under normal conditions only the queen bee and the male drones are capable of reproduction. None of the thousands of workers, who are also females, reproduce. The large number of sterile female worker honeybees collect food, defend the hive, and care for the larvae. As they age, the worker honeybees move through a series of tasks over a period of weeks. When they first emerge from their wax cells, they clean the cells. Several days later, their job is to feed the larvae. Next, they build cells. Later, they become guards, challenging all insects that land near the entrance to the hive. Finally, they become foragers, finding and taking back nectar and pollen to the hive to feed the other bees and to be stored for the winter. Foraging is usually the workers’ last job before they die. Although this progression of tasks is the normal order, workers can shift from their main task to others if there is a need. Both the tasks performed and the progression of the tasks are instinctively (genetically) determined (figure 18.25).

FIGURE 18.25. Honeybee Society

Within the hive, the queen lays eggs, which the sterile workers care for. The workers also clean and repair the hive and forage for food.

Altruism

Altruism is behavior in which an individual animal gives up an advantage or puts itself in danger to aids others. In honeybee societies, the workers give up their right to reproduce and help raise their sisters. Is this a kind of self-sacrifice by the workers, or is there another explanation? In general, the workers are the daughters or sisters of the queen and, therefore, share a large number of her genes. This means that they are helping a portion of their genes get to the next generation by helping raise their own sisters, some of whom will become new queens. This argument has been used to partially explain behaviors in societies that might be bad for the individual but advantageous for the society as a whole.

In other cases, it is not clear that there is any advantage to altruistic behavior. Alarm calls may alert others to a danger but do not benefit the one who gives the alarm. In fact, the one giving the alarm may call attention to itself.

Culture

Culture often develops among social organisms. Extensive contact between parents and offspring allows the offspring to learn certain behavior patterns from their parents. Thus, there are behavioral differences among groups within species. This is obvious in humans, who have various languages, patterns of dress, and many other cultural characteristics. But it is even possible to see similar differences in other social animals. Different groups of chimpanzees use different kinds of tools to get food. Some groups of lions climb trees; others do not (figure 18.26).

FIGURE 18.26. Tree-Climbing Lions

In most of Africa, lions do not climb trees; however, in some areas, they do. The difference is cultural.

Sociobiology

In many ways, honeybee and African wild dog societies are similar. Not all the females reproduce, raising the young is a shared responsibility, and there is some specialization of roles. The analysis and comparison of animal societies has led to the thought that there may be fundamental processes that shape all societies. Sociobiology is the systematic study of all forms of social behavior, both human and nonhuman.

How did various types of societies develop? What selective advantage does a member of a social group have? In what ways are social groups better adapted to their environment than nonsocial organisms? How does social organization affect the way populations grow and change? These are difficult questions because, although evolution occurs at the population level, it is individual organisms that are selected. Thus, new ways of looking at evolutionary processes are needed when describing the evolution of social structures.

The ultimate step is to analyze human societies according to sociobiological principles. Such an analysis is difficult and controversial, however, because humans have a much greater ability to modify behavior than do other animals. However, there are some clear parallels between human and nonhuman social behaviors. This implies that there are certain fundamental similarities among social organisms, regardless of their species. Do we see territorial behavior in humans? “No trespassing” signs and fences between neighboring houses seem to be clear indications of territorial behavior in our social species. Do groups of humans have dominance hierarchies? Most business, government, and social organizations have clear dominance hierarchies, in which those at the top get more resources (money, prestige) than those lower in the organization. Do human societies show division of labor? Our societies clearly benefit from the specialized skills of certain individuals. Do humans treat their own children differently than other children? Studies of child abuse indicate that abuse is more common between stepparents and their nongenetic stepchildren than between parents and their biological children. Although these few examples do not prove that human societies follow certain rules typical of other animal societies, it bears further investigation. Sociobiology will continue to explore the basis of social organization and behavior and will continue to be an interesting and controversial area of study.

18.7. CONCEPT REVIEW

17. Describe why communication is important to successful reproduction.

18. Describe two alternative strategies for assuring that some offspring will survive to continue the species.

19. How do territorial behavior and dominance hierarchies provide certain individuals with an advantage?

20. What distinguishes societies from simple aggregations of individuals?

21. How do animals use chemicals, light, and sound to communicate?

22. What is sociobiology?

Summary

Behavior is how an organism acts, what it does, and how it does it. The kinds of responses organisms make to environmental changes (stimuli) include simple reflexes, very complex instinctive behavior patterns, or learned responses.

From an evolutionary viewpoint, behaviors represent adaptations to the environment. They increase in complexity and variety the more highly specialized and developed the organism is. All organisms have inborn, or instinctive, behavior, but higher animals also have one or more ways of learning. These include habituation, association, exploratory learning, imprinting, and insight. Communication for purposes of courtship and mating is accomplished through sounds, visual displays, touch, and chemicals, such as pheromones. Many animals have behavior patterns that are useful in the care and raising of their young.

Territorial behavior is used to obtain exclusive use of an area and its resources. Both dominance hierarchies and territorial behavior are involved in the allocation of scarce resources. To escape from seasonal stress, some animals estivate or hibernate, others store food, and others migrate. Migration to avoid seasonal extremes requires a timing sense and a way of determining direction. Animals navigate by means of sound, celestial light cues, and magnetic fields.

Societies consist of groups of animals in which individuals specialize and cooperate. Sociobiology attempts to analyze all social behavior in terms of evolutionary principles, ecological principles, and population dynamics.

Basic Review

1. Instinctive behavior differs from learned behavior in that instinctive behavior

a. is inherited.

b. is flexible.

c. is found only in simple animals.

d. is less valuable than learned behavior.

2. The thought that your dog is happy to see you is an example of _____.

3. Imprinting is different from other kinds of learning in that imprinting

a. is of little value to an organism.

b. is not reversible.

c. can be changed easily.

d. can occur at any time during the life of an individual.

4. Learning is a change in behavior as a result of experience. (T/F)

5. All of the following are typical of territorial behavior EXCEPT

a. territorial behavior reserves resources for particular individuals or groups.

b. territorial behavior involves the use of signals to denote territorial boundaries.

c. territorial behavior is found only in higher animals, such as birds and mammals.

d. territorial behavior reduces conflict after territories are established.

6. Social behavior typically involves individuals assuming specialized roles. (T/F)

7. Most methods of communication used by animals are learned. (T/F)

8. A social system in which each animal has a particular ranking in the group is a(n) _____.

9. Most kinds of animals provide no care for their offspring. (T/F)

10. Which of the following provide navigational clues to migrating animals?

a. landmarks, such as rivers and shorelines

b. the magnetic fields of the Earth

c. the stars

d. All of the above are correct.

11. Instinctive behaviors are simple. (T/F)

12. Humans do not learn through association. (T/F)

13. The concept of sociobiology

a. supposes that social behavior has common characteristics in all animals, including humans.

b. does not apply to humans.

c. is applied only to birds and mammals.

d. None of the above is correct.

14. If an organism has instinctive behavior, it probably also has the ability to learn. (T/F)

15. Exploratory learning

a. provides information that an animal can use later in life.

b. is evidence of imprinting.

c. is instinctive.

d. None of the above is correct.

Answers

1. a 2. anthropomorphism 3. b 4. T 5. c 6. T 7. F 8. dominance hierarchy 9. T 10. d 11. F 12. F 13. c 14. T 15. A

Thinking Critically

Talk to the Animals

If you were going to teach an animal to communicate a message new to that animal, what message would you select? How would you teach the animal to communicate the message at the appropriate time?