recap

52.4 recap

Many behaviors are shaped by environmental conditions that influence the decisions animals must make. Decisions can result in benefits that increase reproductive fitness, but they also involve costs, including energetic costs, opportunity costs, and risk costs. Cost–benefit analysis can be applied to territorial and foraging behaviors.

learning outcomes

You should be able to:

  • Describe how a cost–benefit approach is applied to investigating animal behavior.

  • Describe different types of territorial behaviors and the cost and benefit factors that shape their evolution.

  • Explain why aggressive territorial behavior is associated with some essential resources, but not others.

  • Foraging involves trade-offs between nutrients acquired and the costs of energy required, opportunity loss, and risk.

Question 1

Male redwing blackbirds prefer to build nests in marshes, but they feed in upland meadows. What costs and benefits most likely shaped these behaviors?

The benefit of the marsh-nesting site is that it reduces the risk of predation. The cost is that there is greater competition for those sites and less food availability. Feeding in upland areas opens up a greater potential food source, and it does not involve the cost of defending a feeding territory. A risk, however, may be exposure to predation and the need to leave the nest unguarded during feeding.

Question 2

Cichlid fish have dominant males that have colorful markings and defend territories. There are also nondominant males that are plain and do not defend territories but occasionally dash in when a female is spawning to try to fertilize some of her eggs. What are the costs and benefits of these two male phenotypes?

The cost of being a dominant male cichlid is the energetic expenditure involved in territory defense and courtship of females. Also, there are opportunity costs in having less time to feed. The benefit is the likelihood of attracting a mate and fertilizing her eggs. The nondominant male does not incur the costs of territory defense and display and benefits from being able to achieve some reproductive success.

Question 3

Elephant seals defend a piece of beach as a mating territory, whereas prairie-chickens defend small pieces of grassland as a mating territory. Male elephant seals are much larger than the females and viciously fight with one another over their territories. Male prairie-chickens are not much larger than females; they have elaborate displays, and they don’t fight viciously with neighboring males. What selective pressures have shaped the behaviors of these two different kinds of animals that defend mating territories?

Female elephant seals have to have access to a beach to give birth and rear their young, and males can guarantee that access by excluding other males from their piece of beach. Thus the major focus of male elephant seal territorial behavior is exerting physical dominance over other males, and natural selection has optimized the males’ ability to do so. Female elephant seals have no choice over who their “beachmaster” is. In contrast, female prairie-chickens do not need the territory of a male to rear their young, so they are able to simply choose the male they find most attractive. Therefore natural selection in prairie-chickens has favored male displays that are directed at females rather than at other males.

Question 4

Consider a species that has a choice of two potential sources of food. One is calorie-rich, but is dispersed in a sparse environment. The other is calorie-poor but occurs in dense patches in a protected environment. Which types of selective pressures would likely shape the food preference of this species?

One source of selective pressure would be minimization of opportunity costs; therefore the amount of calories obtainable per unit of foraging time would be a critical variable. Another selective pressure is the danger of predation; the relative risk of exposure to predators in the open versus protected environment would be another critical variable.

Behavioral ecologists are interested in understanding how the natural environment influences the fitness value of behavioral choices—the ultimate causes of those behaviors, in Tinbergen’s terms. Other behavioral biologists focus on the physiological mechanisms that underlie the proximate causes of behavior.