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Behavior Ecology
51
BIOLOGICAL SCIENCE
FOURTH EDITION
SCOTT FREEMAN
Lectures by Stephanie Scher Pandolfi
© 2011 Pearson Education, Inc.
Key Concepts
Biologists analyze behavior at the proximate and ultimate levels—
the genetic and physiological mechanisms and how they affect
fitness.
can behave in a wide range of ways; which behavior occurs
depends on current conditions.
Foraging patterns may vary with genotype; foraging decisions
maximize energy gain and minimize costs.
Sexual behavior depends on surges of sex hormones; females
choose mates that provide good alleles and needed resources.
© 2011 Pearson Education, Inc.
Key Concepts
Animals navigate using an array of cues; the costs of migration
can be offset by benefits in food availability.
Animals communicate with movements, odors, or other stimuli;
communication can be honest or deceitful.
Individuals that behave altruistically are usually helping relatives
or individuals that help them in return.
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Introduction
• Behavior is action—a response to a stimulus.
• Ecology is the study of how organisms interact with their physical
and biological environments; behavioral biology is the study of
how organisms respond to particular stimuli from those
environments. The action in behavior is this response.
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An Introduction to Behavioral Biology
• To understand why animals and other organisms do what they do,
researchers have to ask questions about genetics, hormonal signals,
neural signaling, natural selection, evolutionary history, and
ecological interactions.
• Behavioral ecologists ask questions and test hypotheses at two
fundamental levels—proximate and ultimate.
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Proximate and Ultimate Causation
Most behavioral studies start by carefully observing what animals
do in response to specific problems or situations. As research
progresses, investigators use experimental approaches to probe the
proximate and ultimate causes of behavior.
• Proximate (or mechanistic) causation explains how actions
occur.
• Ultimate (or evolutionary) causation explains why actions occur.
• Efforts to explain behavior at the proximate and ultimate levels
are complementary. To understand what an organism is doing,
biologists want to know how the behavior happens and why.
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Proximate and Ultimate Causation
• For example, spiny lobsters are able to find their way back to one
of their dens after a night of hunting.
– On a proximate level, research indicates that they use special
receptors in their brains that detect changes in Earth’s magnetic
field.
– On an ultimate level, the ability to navigate allows them to
search for food over a wide area under cover of darkness, then
return to a safe refuge before predators can find them.
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Conditional Strategies and Decision Making
• In some cases, animals respond to a change in their environment in
a simple, highly predictable way.
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Innate, Inflexible Behavior Is Rare
• Fixed action patterns (FAPs) are highly inflexible, stereotypical
behavior patterns.
• FAPs are examples of innate behavior, behavior that is inherited
and shows little variation based on learning or the individual’s
condition.
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Most Behavior Is Flexible and Condition-Dependent
• Innate behavior is relatively rare. More commonly, behavior
changes in response to learning shows flexibility in response to
changing environmental conditions.
Most animals have a range of actions that they can perform in
response to a situation. Animals take in information from the
environment and, based on that information, make decisions about
what to do.
• This kind of behavior is called condition-dependent behavior.
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Most Behavior Is Flexible and Condition-Dependent
• To link condition-dependent behavior to fitness, biologists use a
framework called cost-benefit analysis.
• Animals appear to weigh the costs and benefits of responding to a
particular situation in various ways.
– Costs and benefits are measured in terms of their impact on
fitness —the ability to produce offspring.
• The decisions made by nonhuman organisms are not—as far as is
known—conscious.
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What Should I Eat?
• When animals seek food, they are foraging.
• In most cases, animals have a relatively wide range of foods that
they exploit over the course of their lifetime.
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Foraging Alleles in Drosophila melanogaster
• Fruit-fly larvae exhibit one of two behaviors during feeding.
– “Rovers” move after feeding in a particular location.
– “Sitters” stay in one location to feed.
• Experiments determined that this feeding behavior is inherited via
the foraging (for) gene.
• Rovers and sitters tend to behave differently when they are foraging
because they have different alleles of the for gene.
• The rover allele is favored at high population density while the
sitter allele reaches high frequency in low-density populations.
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© 2011 Pearson Education, Inc.
Optimal Foraging in White-Fronted Bee-Eaters
When biologists set out to study why animals forage in a
particular way, they usually start by assuming that individuals
make decisions that maximize the amount of usable energy they
take in, given the costs of finding and ingesting their food and the
risk of being eaten while they’re at it.
• This claim is called optimal foraging.
• Researchers found that birds called white-fronted bee-eaters vary
their foraging behavior depending on the distance between their
nesting area and their feeding territory.
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Who Should I Mate With?
Biologists want to know how sexual activity occurs, in terms of
underlying hormonal mechanisms, and why variation in mate
choice affects fitness.
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Sexual Activity in Anolis Lizards
• Anolis lizards have a distinct breeding season, and sexual condition
changes throughout the year.
• Sex hormones—testosterone in males and estradiol in females—are
the proximate cause of dramatic seasonal changes in behavior.
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© 2011 Pearson Education, Inc.
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© 2011 Pearson Education, Inc.
Sexual Activity in Anolis Lizards
• A series of experiments indicate that two types of stimulation are
necessary to produce the hormonal changes that lead to sexual
behavior.
– Females need to experience springlike light and temperatures,
as well as exposure to breeding mates.
• Males signal females and induce estradiol release by exhibiting a
specific mating signal. When males court females, they bob up and
down and extend a brightly colored patch of skin called a dewlap.
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How Do Female Barn Swallows Choose Mates?
• Females are usually the gender that is pickiest about mate choice.
– Females choose males that contribute good alleles and/or
resources to their offspring.
• Although both male and female barn swallows help build the nest
and feed the young, the species exhibits a significant amount of
sexual dimorphism—males are slightly larger and more brightly
colored, and their outer tail feathers are about 15 percent longer
than the same feathers in females.
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How Do Female Barn Swallows Choose Mates?
• Experiments supported the hypothesis that female barn swallows
prefer long-tailed mates.
– Long-tailed males are more efficient in flight and more
successful in finding food, and thus have higher fitness.
– He will also pass high-fitness alleles on to her offspring and be
able to help her rear those offspring efficiently.
• Data on mate choice in barn swallows reinforce a central theme:
Animals usually make decisions in a way that maximizes their
fitness.
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Where Should I Live?
• There are many questions related to habitat selection:
– Should juveniles disperse from the area where they were
raised?
– How large of a territory should be defended against
competitors.
– How do habitat density and quality affect fitness?
• Addressing the proximate and ultimate mechanisms responsible for
migration — the long-distance movement of a population
associated with a change of seasons—relates to these questions of
habitat selection.
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How Do Animals Find Their Way on Migration?
• Biologists distinguish three categories of navigation:
1. Piloting is the use of familiar landmarks.
2. Compass orientation is movement oriented in a specific
direction.
3. True navigation is the ability to locate a specific place on
Earth’s surface.
• Biologists understand little about true navigation, but piloting and
compass orientation are increasingly well understood.
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Piloting
• Many species use piloting to find their way.
• In some species of migratory birds and mammals, offspring seem to
memorize the route by following their parents south in the fall and
north in the spring.
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Compass Orientation
• Birds and perhaps other organisms have multiple mechanisms for
finding a compass direction.
• At least some species can use a Sun compass, a star compass, and a
magnetic compass.
• Which system they use depends on the weather and other
circumstances.
• The Sun is difficult to use as a compass reference, because its
position changes throughout the day.
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© 2011 Pearson Education, Inc.
Compass Orientation
• Most animals have a circadian clock that maintains a 24-hour
rhythm of chemical activity. The clock is set by the light-dark
transitions of day and night and tells an animal enough about the
time of day that it can use the Sun’s position to find magnetic north.
• On clear nights, migratory birds in the Northern Hemisphere can
use the North Star to find magnetic north.
• During cloudy weather, birds appear to orient themselves using
Earth’s magnetic field.
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Homing Behavior in Digger Wasps
Web Activity: Homing Behavior In Digger Wasps
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Why Do Animals Move with a Change of Seasons?
• At the ultimate level, migration exists because individuals that
migrate achieve higher reproductive success than individuals that
do not migrate.
Increased access to food is a benefit of migration. There is a high
cost, however, in time, energy, and predation risk.
• At the proximate level, explaining migratory movements is often
extremely difficult.
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How Should I Communicate?
• Communication is a process in which a signal (any informationcontaining behavior) from one individual modifies the behavior of
another individual.
• Communication is a social process. For communication to occur, it
is not enough that a signal is sent; the signal must be received and
acted on.
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Honeybee Language
• Honeybees are highly social animals that live in hives, in which a
queen bee lays eggs that are cared for by workers.
• Besides caring for young and building and maintaining the hive,
workers obtain food for themselves and other members of the
colony.
• Researchers hypothesized that successful food-finders have some
way of communicating the location of food to other individuals.
• At the ultimate level, this communication is easily understood.
However, researchers were unsure of the proximate mechanism of
communication.
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The Dance Hypothesis
• Karl von Frisch suspected that honeybees that are successful in
finding food communicate the location of food to other honeybees
in their hive.
• He observed bees displaying a “round dance” to workers, as well as
a “waggle dance.”
• Other worker bees follow the progress of the dance by touching the
displaying individual.
• Von Frisch found that both the round dance and the waggle dance
communicate information about food sources.
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Communicating Directions and Distances
• The round dance is used to indicate the presence of food within 80–
100 m from the hive, while the waggle dance indicates the direction
and distance to food over 100 m from the hive.
• The orientation of the waggle dance correlated with the direction of
the food source from the hive, and the length of the straight
waggling run was proportional to the distance the foragers had to
fly to reach the food.
• This dance also communicated the position of the food relative to
the current position of the Sun.
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© 2011 Pearson Education, Inc.
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Modes of Communication
• Several modes of communication are often used together.
Communication can be tactile, olfactory, acoustic, or visual. The
type of signal an organism uses correlates with its habitat.
• Each mode of communication has advantages and disadvantages.
Communication systems have been honed by natural selection to
maximize their benefits and minimize their costs.
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When Is Communication Honest or Deceitful?
At the ultimate level, one of the questions that biologists ask about
communication concerns the quality of the information. Is the
signal reliable?
• In some cases, it is advantageous for an individual to convey
information accurately.
• In other cases, natural selection has favored the evolution of
deceitful communication, or lying.
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Deceiving Individuals of Another Species
• Individuals sometimes increase their fitness by providing inaccurate
or misleading information to members of a different species.
• For example:
– The anglerfish dangles a minnow-like appendage near its
mouth and attacks another fish that approaches and attempts to
eat this “lure.”
– Male and female fireflies flash species-specific signals to each
other during courtship. Predatory Photuris firefly females
attract a male of different species with the appropriate set of
flashes, and then attack and eat him.
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Deceiving Individuals of the Same Species
• In some cases, natural selection has also favored the evolution of
traits or actions that deceive members of the same species.
• For example, some male bluegills will mimic females—these fish
look like females and even act like them during courtship with
territory-owning males. The territory-owning male thinks he is
courting two females.
• When the actual female begins to lay eggs, the mimic releases
sperm and fertilizes some of the eggs. In this way the female-mimic
male fathers offspring but does not help care for them.
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When Does Deception Work?
• Deceit works only when it is relatively rare; if it becomes common,
natural selection will strongly favor individuals that can detect and
avoid or punish liars.
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When Should I Cooperate?
• Most behaviors help individuals respond to environmental stimuli
such that they can maximize their own fitness. Altruism, behavior
that has a fitness cost to the individual exhibiting it and a fitness
benefit to the recipient, appears to contradict this pattern.
• Altruism decreases an individual’s ability to produce offspring but
helps others produce more offspring.
• The existence of altruistic behavior appears to be paradoxical;
alleles that make an individual more likely to be altruistic should be
selected against.
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Kin Selection
• Self-sacrificing behavior occurs in nature.
• For example, black-tailed prairie dogs perform a risky behavior
called alarm calling. Researchers have shown that alarm-callers
draw attention to themselves by calling and are in much greater
danger of being attacked than non-callers are.
• William D. Hamilton addressed the question of how natural
selection can favor the evolution of self-sacrificing behavior.
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Hamilton’s Rule
• Hamilton’s rule can be expressed as Br > C, where B is the fitness
benefit to the beneficiary, r is the coefficient of relatedness, and C
is the fitness cost to the actor.
• Hamilton’s rule states that altruistic behavior is most likely when
three conditions are met:
1. The fitness benefits of altruistic behavior are high for the
recipient.
2. The altruist and recipient are close relatives.
3. The fitness costs to the altruist are low.
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Calculating the Coefficient of Relatedness
• The coefficient of relatedness, r, varies between 0.0 and 1.0.
– If two individuals have no identical alleles that were inherited
from the same ancestor, then their r value is 0.0.
– Because every allele in pairs of identical twins is identical, their
coefficient of relatedness is 1.0.
• In each parent-to-offspring link of descent, the probability of any
particular allele being transmitted is ½.
• Researchers calculate the coefficient of relatedness using
information in pedigrees.
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Hamilton’s Rule
• When Hamilton’s rule holds, alleles associated with altruistic
behavior will be favored by natural selection—because close
relatives are very likely to have copies of the altruistic alleles.
• Hamilton’s rule is important because it shows that individuals can
pass their alleles on to the next generation not only by having their
own offspring, but also by helping close relatives produce more
offspring.
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Inclusive Fitness
• Biologists refer to direct fitness and indirect fitness.
– Direct fitness is derived from an individual’s own offspring.
– Indirect fitness is derived from helping relatives produce more
offspring than they could produce on their own.
• The combination of direct and indirect fitness components is called
inclusive fitness.
• Kin selection is natural selection that acts through benefits to
relatives and results in increased indirect fitness.
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Testing Hamilton’s Rule
• To test the kin-selection hypothesis, a researcher studied which of
the inhabitants of a black-tailed prairie dog town were most likely
to give alarm calls.
• It was determined within each small group—or coterie—whether
each individual had:
1. No close genetic relatives in its coterie.
2. No offspring in the coterie but at least one sibling, cousin,
uncle, aunt, niece, or nephew.
3. At least one offspring or grandoffspring in the coterie.
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Testing Hamilton’s Rule
• The kin-selection hypothesis predicts that individuals who do not
have close genetic relatives nearby will rarely give an alarm call.
• The data indicate that black-tailed prairie dogs are much more
likely to call if they live in a coterie that includes close relatives.
This same pattern—of preferentially dispensing help to kin—has
been observed in many other species of social mammals and birds.
Most cases of self-sacrificing behavior that have been analyzed to
date are consistent with Hamilton’s rule and are hypothesized to be
the result of kin selection.
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© 2011 Pearson Education, Inc.
© 2011 Pearson Education, Inc.
Reciprocal Altruism
• Reciprocal altruism is an exchange of fitness benefits that are
separated in time.
• For example, experimental evidence has shown:
– Vervet monkeys are most likely to groom unrelated individuals
that have groomed or helped them in the past.
– Vampire bats are most likely to donate blood meals to non-kin
that have previously shared food with them.
• Reciprocal altruism is also widely invoked as an explanation for the
helpful and cooperative behavior commonly observed among
unrelated humans.
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An Extreme Case: Abuse of Non-Kin in Humans
• Martin Daly and Margo Wilson helped pioneer the use of “selection
thinking” in studies of human behavior.
• They gathered data on child abuse and hypothesized that selection
should favor parents who invest resources in biological children but
not in stepchildren—with whom the parents have no genetic
relationship.
• They found that kids who are less than 2 years old are 70 times
more likely to be killed in a household with a stepparent than in a
household with only biological parents.
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© 2011 Pearson Education, Inc.