Behavior Ecology

1. Behavior Ecology 51

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

9. Conditional Strategies and Decision Making • In some cases, animals respond to a change in their environment in a simple, highly predictable way.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

16. 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.

20. 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.

21. 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.

25. 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.

27. 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.

29. 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.

34. 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.

35. How Do Animals Find Their Way on Migration? • Biologists distinguish three categories of navigation: • Piloting is the use of familiar landmarks. • Compass orientation is movement oriented in a specific direction. • 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.

36. 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.

37. 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.

39. 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.

40. Homing Behavior in Digger Wasps Web Activity: Homing Behavior In Digger Wasps

41. 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.

42. 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.

43. 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.

44. 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.

48. 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.