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BIO153 Ch 51 Notes.pdf

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Christoph Richter

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Freeman, Biological Science, 4e, Chapter 51 Chapter 51 – Behavioral Ecology Learning Objectives: Students should be able to … • Explain proximate and ultimate causes of behavior and how genetic and physiological mechanisms affect fitness. • Describe how foraging decisions maximize energy gain and minimize costs. • Explain how sexual hormones affect behavior, and explain female mate choice. • Describe the various cues that animals use to navigate. • Describe the various ways in which animals communicate. • Explain why animals might behave altruistically. Lecture Outline I. An Introduction to Behavioral Biology A. Proximate and ultimate causation 1. Proximate causation explains how actions occur. 2. Ultimate causation explains why actions occur. 3. For example, spiny lobsters spend the day hiding in cracks and holes in the coral reef; at night, they emerge and wander in search of food. How do they find their way back? (Fig. 51.1) 4. The proximate and ultimate levels of causation are complementary. To understand what an organism is doing, biologists want to know how the behavior happens and why. B. Conditional strategies and decision making 1. Innate, inflexible behavior is rare. a. Highly inflexible behavior patterns are called fixed action patterns (FAPs). b. FAPs are examples of innate behavior—that is, types of behavior that are inherited and show little variation based on learning. 2. Most behavior is flexible and condition-dependent. a. Although all species studied to date show some degree of innate behavior, it is much more common for an individual’s behavior to change in response to learning and show flexibility in response to changing environmental conditions. b. Animals take information from the environment and make decisions about what to do based on that information; animals make choices. c. Cost-benefit analysis: Animals appear to weigh the costs and benefits of responding in various ways, based on their impact on fitness. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 51 II. What Should I Eat? A. Animals forage for food. 1. Animals forage in a way that maximizes 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. B. Foraging alleles in Drosophila melanogaster 1. Marla Sokolowski discovered an important behavioral trait controlled by a single gene. She noticed that some fruit-fly larvae tended to move away from food after eating, while others remained in place. 2. By breeding “rovers” and “sitters” that possessed other distinct genetic markers, Sokolowski and colleagues were able to map the gene responsible for the behaviors. (Fig. 51.2) C. Optimal foraging in white-fronted bee-eaters 1. To test whether optimal foraging actually occurs, researchers studied the eating behavior of white-fronted bee-eaters. 2. White-fronted bee-eaters appear to make decisions that maximize the energy they deliver to their offspring, given their costs of finding food. This behavior is highly flexible and would change in a way that maximizes its fitness. (Fig. 51.3) III. Who Should I Mate With? A. Sexual activity in Anolis lizards 1. Males become active in January and begin establishing territories. (Fig. 51.4a) 2. Females lay an egg every 10–14 days. By the end of the breeding season, females will lay an amount of eggs equal to twice their body mass. 3. What causes these dramatic seasonal changes in behavior? (Fig. 51.4b) At the proximate level, these seasonal changes in behavior are caused by the sex hormones testosterone and estradiol. 4. What environmental cues trigger hormonal secretion? a. Researchers captured inactive Anolis lizards and placed them in five treatment groups in the laboratory, all in springlike environmental conditions: (1) Single isolated female (2) Group of females (3) Single female with a single male (4) Single female with a group of castrated males (5) Single female with a group of breeding males b. The control group was females in the wild, who were inactive, and in winter conditions. c. Experiment: Check the ovaries of females in all groups to determine when they begin to produce eggs. d. Results: Two types of stimulation are necessary to produce the hormonal changes that lead to sexual behavior in female lizards: (Fig. 51.5) © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 51 (1) Springlike light and temperature conditions (2) Exposure to males displaying courtship behavior (a) Males displaying their dewlaps stimulated females. (b) Males lacking a dewlap did not stimulate females. 5. The data suggest that the dewlap is a key visual signal that triggers hormone production and the onset of sexual behavior. B. How do female barn swallows choose mates? 1. Male barn swallows are slightly larger and more brightly colored than females. Their tail feathers are about 15% longer. (Fig. 51.6) 2. The hypothesis is that female barn swallows choose a mate with a long tail, which is indicative of high fitness. 3. Biologists caught a large group of males and randomly assigned them to groups: short tails, unchanged tails, untouched tails, or elongated tails. (Fig. 51.7) 4. Females preferred to mate with long-tailed males. 5. Data from this experiment reinforced the fact that animals make decisions in a way that maximizes their fitness. IV. Where Should I Live? A. Animals select their habitats. 1. Biologists have explored an array of questions related to habitat selection. a. Whether or not juveniles should disperse to a new area b. How large a territory should be defended c. Whether high-quality, crowded habitats are better than low- quality, uncrowded habitats 2. Migration is the long-distance movement of a population associated with a change in seasons. B. How do animals find their way on migration? 1. Many species use piloting, or using familiar landmarks, to find their way. a. Young offspring follow their parents during migrations and appear to memorize the route. b. Homing pigeons can always find their way back home, but if their eyes are covered, they fail to navigate just the final stage, suggesting they may use piloting for the final part of a journey. 2. Compass orientation is using a reference to determine where north is. (Fig. 51.8) a. To determine where north is, homing pigeons appear to use the Sun during the day and the stars at night. During cloudy conditions, these birds appear to use Earth’s magnetic field to orient. b. To use the Sun as a reference, the animals must have a circadian clock that maintains a 24-hour rhythm of chemical activity. c. Although research on mechanisms of compass orientation continues, one point is clear: Birds and perhaps other © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 51 organisms have multiple mechanisms of finding compass direction. d. At least some species can use a Sun compass, a star compass, and a magnetic compass. Which systems they use depends on the weather and other circumstances. C. Why do animals move with a change of seasons? 1. Migratory movements can be spectacular. 2. Arctic terns a. Arctic terns nest along the Atlantic coast of North America, fly south along the coast of Africa to wintering grounds off Antarctica, and then fly back along the eastern coast of South America. b. They feed on fish that are available in different parts of the world in different seasons. 3. Monarch butterflies a. Many of the monarch butterflies native to North America spend the winter in the mountains of central Mexico or southwest California. b. They may achieve higher reproductive success by migrating compared to overwintering. 4. Salmon a. Salmon that hatch in rivers along the Pacific Coast of North America and northern Asia migrate to the ocean when they are a few months to several
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