behavior ecology

© 2011 Pearson Education, Inc.

Lectures by Stephanie Scher Pandolfi

BIOLOGICAL SCIENCE

FOURTH EDITION

SCOTT FREEMAN

51Behavior Ecology


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.


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.


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.


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.


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.


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.


Conditional Strategies and Decision Making

• In some cases, animals respond to a change in their environment in a simple, highly predictable way.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


Homing Behavior in Digger Wasps

Web Activity: Homing Behavior In Digger Wasps


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.


How Should I Communicate?

• Communication is a process in which a signal (any information-containing 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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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.


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:

– The fitness benefits of altruistic behavior are high for the recipient.

– The altruist and recipient are close relatives.

– The fitness costs to the altruist are low.


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.


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.


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.


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.


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.


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.


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.

behavior ecology

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