Mastering Concepts
36.1
1. What is ethology?
Ethology is the scientific study of animal behavior, especially in the natural environment.
2. Distinguish between the proximate and ultimate causes of an animal’s behavior.
A proximate cause of a behavior is the anatomical or physiological mechanism that
makes it happen. An ultimate cause of a behavior reflects its contribution to survival or
reproduction.
36.2
1. What is the traditional distinction between innate and learned behaviors?
Innate behaviors are instinctive behavior patterns that do not involve learning and that
tend to be stereotypical in nature; traditionally they were viewed as under the control of
“nature” (genetic control). Learned behaviors are modified in response to an animal’s
experiences; traditionally they were seen as under the influence of “nurture”
(environmental control).
2. Describe three examples of innate animal behaviors.
Innate animal behaviors include reflexes, taxes, and fixed action patterns. Reflexes are
instantaneous, automatic responses to a stimulus. For example, a startle reflex makes
your eyes close if an object suddenly approaches your head. Taxis behaviors involve
movement toward or away from a stimulus. For example, a male moth flies toward the
source of a female’s pheromone. Fixed action patterns are triggered by an environmental
stimulus and go to completion even if the stimulus is withdrawn. For example, the sight
of an egg outside its nest triggers a fixed action pattern by which a goose returns the egg
to the nest.
3. Name four types of learning.
Four types of learning are habituation, associative learning, imprinting, and observational
learning.
4. What are some examples of animal cognition?
Examples of animal cognition include reasoning, problem solving, tool use, and
communication by sign language or symbols.
5. How does song learning in birds illustrate how genes and experience interact to
determine an animal’s behavior?
Young male song sparrows instinctively begin to sing, indicating a genetic influence on
singing behavior. However, a young sparrow that hears no song, or that hears the song of
another species, will perform an abnormal song. The sparrow will learn to sing normally
only if exposed to songs of its own species during a critical period. This observation
indicates the influence of experience on a basic genetic template in the song-learning
process.
36.3
1. What are four mechanisms by which animals find their way to a specific location?
Three mechanisms are orientation, path integration, piloting, and true navigation. In
orientation, the animal adjusts its position relative to the sun, stars or magnetic fields. In
path integration, the animal integrates information about speed and direction to estimate
its location. In piloting, the animal uses distant objects as a guide. In true navigation, an
animal understands its current position and plots a course to its destination without
relying on stimuli from that location.
2. Describe how optimal foraging theory explains an animal’s foraging decisions.
Optimal foraging theory states that animals will maximize their energy returns for each
unit of time spent foraging. An animal’s optimal strategy reflects a trade-off between the
calories in the food versus time spent searching for, obtaining, and handling the food.
3. What are some behaviors that help animals avoid predation?
Specialized body markings and behaviors help some animals hide from predators. Some
animals reveal markings that resemble those of predators, whereas others deploy sharp
quills or release toxic chemicals when threatened. Distraction displays may divert a
predator from a nest or den. Groups of animals may stot, mob, or use alarm calls to avoid
predators.
36.4
1. List three functions of animal courtship rituals.
Courtship displays ensure that the male and female are of the same species. They also
coordinate physiological and hormonal responses between the pair. Finally, courtship
displays allow each to gauge the suitability of the other as a mate.
2. Describe examples of intrasexual selection and of intersexual selection.
Intrasexual selection occurs when males compete with one another for exclusive access to
females. Examples of traits that reflect intrasexual selection include the size of the
proboscis in elephant seals and the size of antlers in deer. Intersexual selection occurs
when females choose among multiple males. Examples of traits that reflect intersexual
selection include a peacock’s tail and the color of a rooster’s comb.
3. What is the relationship between sexual dimorphism and mating systems?
Species that are polygamous typically display sexual dimorphic characteristics. Species
that are monogamous are typically not sexually dimorphic.
4. Explain how confidence of paternity influences the degree of parental care by a male.
If a male has low confidence that he is the father of a female’s offspring, then he is
unlikely to spend energy caring for the young. He enhances his fitness by spending his
energy seeking additional mates instead. On the other hand, if a male has high confidence
of paternity, he enhances his fitness by helping to care for the young, ensuring the
survival of the offspring.
5. How do observations of reproductive behavior in nonhuman animals enable
researchers to make predictions about humans?
First, women invest more in rearing offspring than do men; therefore, one prediction is
that women should be choosier than men in selecting mates. Second, in species with
sexual dimorphism, monogamy is not the rule. Humans show sexually dimorphic
characteristics, so it is not surprising that men have multiple wives in many societies.
Third, in nonhuman animals, males invest more in offspring when they have greater
confidence that the offspring are theirs. This observation translates to forms of mate
guarding that boost a man’s confidence of paternity.
36.5
1. What are some benefits and costs of group living?
Benefits include the ability to share information (e.g., about food and resources) and
enhanced protection (e.g., from cold and from predators). Costs include higher
competition for food and mates; diseases also spread easily within a group. A group may
also be more visible to predators than individual organisms.
2. Explain the roles of dominance hierarchies and territoriality in animal societies.
Dominance hierarchies assign mating rank within a group, reducing competition for
mates. Territoriality provides individuals or groups of animals with exclusive access to
resources within a defended area.
3. Define altruism and explain why evolution should select against it.
In altruism, an individual reduces its own fitness to help an unrelated individual, with no
benefit to itself. Because altruism reduces fitness, natural selection should “weed out”
animals that exhibit altruism.
4. What is eusociality?
Eusociality is a social division of labor, especially concerning mating. Typical traits of
eusocial animals include cooperative care of young, the presence of sterile castes that
help care for breeding animals, and the care of young by older siblings.
36.6
1. Why does evolution select for males that mimic females, even though the chance of
success is relatively low?
Although the success rate of disguised males may seem low (about 3% of the mimics
ultimately fathered offspring), small males that do not disguise themselves as females
have an even lower chance of fathering offspring. The deceptive behavior is therefore
favored.
2. How would you test the hypothesis that the offspring of a mate-guarding male is more
likely to guard his mate than is the offspring of a “sneaker” male? What does this
hypothesis assume about the inheritance of mate guarding?
One experimental design could be to tag male cuttlefish at birth as offspring of either
mate-guarding males or “sneaker” males. These offspring could then be observed for
guarding and sneaking behavior after they are sexually mature. This hypothesis assumes
that mate guarding behavior has a genetic basis.
Write It Out
1. Classify each of the following descriptions as either a proximate or an ultimate cause
of behavior. For all proximate causes, speculate about a possible ultimate cause of the
behavior.
a. A surge of epinephrine initiates a flight response in a gazelle.
b. Turtles use Earth’s magnetic field lines as guides during migration.
c. A small mammal ignores low-energy food sources that are difficult to obtain,
maximizing energy gain from foraging.
d. A bird distracts a predator near its nest, increasing the nestlings’ chance of
survival.
Scenarios a and b describe proximate causes of behavior, whereas c and d describe
ultimate causes. For scenario a, the ultimate cause of the behavior is that gazelles that flee
at the sight of a predator are more likely to survive than those that do not. For scenario b,
the ultimate cause of the behavior is that turtles that use the shortest path to reach feeding
or mating grounds have the most energy available for mating or rearing young.
2. In what way is a taxis similar to and different from a tropism in a plant (see chapter
24)? Give an example of a taxis and a tropism.
In both instances the organism is directing its movement toward or away from a stimulus.
A taxis is based on the movement of an entire animal; a tropism is based on differential
growth in a plant. A scorpion tends to move away from light; this behavior is a taxis. A
plant in a windowsill may grow toward light; this phenomenon is a tropism.
3. Give an example of a fixed action pattern.
Many answers are possible, but one example of a fixed action pattern is the behavior of
the praying mantis when it catches and eats its prey.
4. What do nonthreatening odors, repetitive sounds, and constant touch have in common?
Animals are likely to habituate to all of these stimuli.
5. Explain how biologists identify genes controlling behavior in a fruit fly. Why might it
be difficult to identify similar genes in humans?
Biologists can use chemicals or radiation to cause mutations in fruit fly genes and then
observe the behavior of the resulting mutant organisms. Although it is possible to search
the human genome for genes that are homologous to fruit fly genes, it is unethical to
intentionally mutate genes in humans and then observe any changes in the person’s
behavior.
6. Male thynnine wasps approach and attempt to mate with female wasps that release
pheromones. Some orchid flowers emit a chemical that mimics the female wasp’s
pheromone so convincingly that male wasps will attempt to copulate with the flower.
Once a male visits a flower, however, he avoids the same flower in the future. How does
this example illustrate the interaction between innate and learned behaviors? What type
of learning has occurred in the male?
The example illustrates innate behaviors because male wasps instinctively try to mate
with anything that emits female pheromones. However, the male wasps eventually learn
to avoid orchids. The specific type of learning is associative learning (operant
conditioning), as a male wasp learns to associate the orchid with an unsuccessful mating
attempt and does not repeat the behavior.
7. For multiple decades, scientists in Russia have selectively bred one group of foxes for
aggression and bred a second group for friendliness toward humans. The offspring of
aggressive foxes tend to be aggressive, while those of friendly foxes tend to be friendly.
What do these results reveal about whether a fox’s disposition is influenced by genes or
the environment? What type of disposition would you predict for a baby fox captured
from the wild?
In foxes, disposition is an inherited trait. The behaviors associated with aggression or
friendliness are subject to artificial selection and are therefore genetically encoded. In the
wild, aggression is more likely to contribute to reproductive success than is friendliness.
A baby fox captured from the wild is therefore likely to be aggressive, although with
prolonged contact it may eventually learn to tolerate humans.
8. European cuckoos and American cowbirds are “brood parasites” that lay their eggs in
the nests of other birds. The chicks are generally raised by “adoptive parents” whose own
chicks receive less food and often are killed by the larger intruders. What kinds of
behaviors does natural selection favor in the cuckoo and cowbird chicks? In the adoptive
parents?
In cuckoo and cowbird chicks, natural selection favors aggressive behavior that
eliminates rivals from the nest. In adoptive parents, natural selection favors well-hidden
nests, denying access to the nest by adult cuckoos and cowbirds, the production of
multiple broods consisting of many offspring, and the ability to discriminate between
their own offspring and the cuckoo or cowbird chicks.
9. Prey animals may use distraction displays when a predator is nearby. What selective
pressures do these prey animals exert on predators? Explain why distraction displays may
become more convincing through evolutionary time
Animals that use deceptive behaviors, like distraction displays, to avoid predation are
likely to select for predators that can detect deception. In turn, predators that are not
fooled by deception will select for prey with more convincing distraction displays.
10. Why don’t animals exhibit true altruism?
True altruism would occur when an animal reduces its own fitness while improving the
fitness of an unrelated individual. An animal with reduced fitness has fewer offspring
surviving to maturity; therefore, an altruistic behavior would be selected against, as
individuals without the behavior would have more surviving offspring.
11. What are some of the costs and benefits of associating with a group? Can you think of
some costs and benefits not mentioned in this chapter?
Costs include easier detection by predators that detect large groups, increased
competition for some resources, and easier spread of disease. Additional costs might be
increased competition for mates, including the possibility of not mating at all. Benefits
include greater protection from cold or predators, and cooperation in finding food.
Additional benefits might include multiple models for learned behaviors and the
availability of extra helpers in parental care.
12. In the 1930s, the population geneticist J. B. S. Haldane famously said, “I would lay
down my life for two brothers or eight cousins.” What was he talking about?
You share half your genes with each of your siblings, so two brothers would, on average,
share 100% of your genes. You share 1/8 of your genes with your cousins, so the eight
cousins would also total 100%.
Pull it Together
1. Add foraging, habituation, kin selection, fixed action pattern, eusocial animals,
inclusive fitness, imprinting, and reciprocal altruism to this concept map.
“Foraging” connects with “is a behavior that enhances” to “Survival.” “Habituation” and
“Imprinting” connect with “are forms of” to “Learning.” “Kin selection,” “Inclusive
fitness,” and “Reciprocal altruism” connect with “may explain some forms of” to
“Cooperation.” “Fixed action pattern” connects with “is a type of” to “Innate behavior.”
“Eusocial animals” connects with “exhibit distinctive patterns of” to “Social
interactions.”
2. Select one of the three boxes under “Reproduction” in the diagram. For your selected
box, provide a specific example of an animal behavior. What is the proximate and
ultimate cause of the behavior you described?
[Answers will vary.]