CONCEPTS IN BIOLOGY

PART IV. EVOLUTION AND ECOLOGY

 

18. Evolutionary and Ecological Aspects of Behavior

 

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Urban Coyotes Kill Pets

What can be done to solve the problem

Coyotes have adapted to urban and suburban locations where there are natural areas such as parks, golf courses, drainage ditches, and similar places that provide suitable habitat. Reports of coyotes killing pets, particularly cats and small dogs, are common throughout the United States. What has happened to make this wary animal lose its fear of humans?

Humans have contributed to this problem by providing several sources of food that are attractive to wild animals. Animals like coyotes learn to associate food with humans. The three most common sources of food are (1) garbage that is not in a secure container; (2) pet food provided outdoors; and (3) bird feeders. Coyotes are scavengers as well as carnivores and will use these sources of food. Once coyotes become habituated to finding food around homes, they are likely to encounter pets that are outside the home. Cats that roam at night are particularly vulnerable to predation by coyotes.

• Why do coyotes lose their fear of humans?

• Can coyotes be trained to avoid humans?

• In areas with a coyote problem, should homeowners be required to place garbage in a secure container, stop feeding birds, and keep their pets indoors?

 

ü  Background Check

Concepts you should already know to get the most out of this chapter:

• How natural selection shapes the evolution of organisms (chapter 13)

• The difference between a scientific test of a hypothesis and an opinion (chapter 1)

 

18.1. Interpreting Behavior

 

Behavior is how an animal acts—what it does and how it does it. When you watch a bird, a squirrel, or any other animal, its activities appear to have a purpose. Birds search for food, take flight as you approach, and build nests in which to raise young. Usually, the nests are inconspicuous or placed in difficult-to-reach spots. Likewise, squirrels collect and store nuts and acorns, “scold” when you get too close, and learn to visit sites where food is available.

 

Discovering the Significance of Behavior

It is not always easy to identify the significance of a behavior without careful study of the behavior pattern and its impact on other organisms. For example, a baby herring gull pecks at a red spot on its parent’s bill. What possible value can this behavior have for either the chick or the parent? If we watch, we see that, when the chick pecks at the spot, the parent regurgitates food onto the ground, and feeds it to the chick (figure 18.1). This looks like a simple behavior, but there is more to it than meets the eye. Why did the chick peck to begin with? How did it “know” to peck at that spot? Why did the pecking cause the parent to regurgitate food? These questions are not easy to answer. Many people assume that the actions have the same motivation and direction as similar human behaviors, but this is not necessarily a correct assumption. For example, when a little girl points to a piece of candy and makes appropriate noises, she is indicating to her parent that she wants some candy. Is that what the herring gull chick is doing? We don’t know. Although both kinds of young may get food, we don’t know what the baby gull is thinking because we can’t ask it.

 

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FIGURE 18.1. Understanding Behavior

A herring gull chick causes its parent to regurgitate food onto the ground by pecking at the red spot on its parent’s bill. This behavior is instinctive. The parent then picks up the food and feeds it to the chick.

 

Behavior Is Adaptive

When we observe behavior, we must keep in mind that behavior is adaptive just like any other characteristic displayed by an animal. Behaviors are important for survival and appropriate for the environment in which an animal lives. As with animals’ highly adaptive structural characteristics, behaviors are the result of a long evolutionary process. Birds that do not take flight at the approach of another animal are eaten by predators. Squirrels that do not find deposits of food are less likely to survive, and birds that build obvious nests on the ground are more likely to lose their young to predators.

Because the nervous system of animals is the product of genes, many aspects of behavior have a genetic component. In this respect, behavioral characteristics are no different from physical characteristics, such as eye structure, wing shape, or tail length. However, the evolution of behavior is much more difficult to study than structural characteristics. This is because behavior is temporary, and it is difficult to find fossils that show the development of behavior, the way fossils allow us to follow changes in structures. Fossils of footprints, nests, and specific structures such as teeth adapted for grinding give clues about the behavior of extinct animals (How Science Works 18.1). However, these examples represent only a few fragments of the total behavior that must have been a part of the lives of extinct animals. When scientists compare the behavior of closely related animals living today, they can see inherited behaviors that are slightly different from one another. This strongly suggests that these behaviors have evolved, just as the wings of different species of birds have evolved for different kinds of flight. In both cases (structural and behavioral) a basic pattern has been modified as the organisms adapted to their environments.

 

HOW SCIENCE WORKS 18.1

Males Raised the Young in Some Species of Dinosaurs

Sometimes it is possible to use fossils to gain insight into the behavior of extinct animals. In 2008, scientists published a study that suggests that some kinds of theropod dinosaurs (Oviraptor, Troodon, Citipati) had a mating system in which the male dinosaurs were the primary caregivers for young. The male dinosaurs guarded the eggs in the nest and cared for the young after the eggs hatched. They based their assertion on several lines of evidence. Fossils of adult dinosaurs have been found associated with nests of eggs and the position of the adult is consistent with it protecting the nest. The dinosaurs that show this behavior show many birdlike characteristics and are closely related to species of birds that show male brooding of young—kiwi, ostrich, and emu. The number of eggs in the nest is large. Birds in which males brood the eggs and raise the young have large numbers of eggs. They compared the number of eggs in the nest of the dinosaurs with that of modern dinosaur relatives—crocodiles, alligators, and birds—and found that the number of eggs in the nest closely matched that of birds in which males brood the eggs. Finally, they compared the bone structure of the dinosaurs found guarding the nest and determined that the bones lacked a layer of spongy bone inside their long bones. Female birds produce this spongy bone during reproduction. The absence of this feature strengthens the argument that the individual guarding the nest were males.

This has significant implications for our understanding of the evolution of bird behavior. Perhaps the first birds were those in which males cared for the young, and the common pattern we see today—both parent birds caring for the young—has evolved from the more primitive condition found in ostriches and their relatives.

 

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18.1. CONCEPT REVIEW

1. Why is it more difficult to study the evolution of behavior than the evolution of structural characteristics?

2. List two animal behaviors and state their significance to the animal’s reproductive success.