Foraging Energetics and Risk

点击翻译按钮获取中文摘要

Maintaining or managing a natural system requires that we understand the survival strategies of the organisms that make up the system. We can gauge our level of understanding by our ability to predict how survival strategies will change as the environment changes. Many animals, especially small birds and mammals, must find and consume enough food to meet their energy expenditures each day, or face the possibility of starving overnight (when darkness interrupts foraging). In an environment where food rewards vary randomly, theory predicts that the foraging behavior of such animals depends on a comparison of expected daily energy intake with daily energy expenditures. Given a particular average level of food rewards, foragers should avoid food resources with high reward variability when expected energy intake exceeds expenditures (i.e., average benefits exceed costs). However, foragers should prefer high reward variability when necessary expenditures exceed expected energy intake (i.e., costs exceed average benefits). Dr. Caraco's previous experiments supported the theory. In that work, daily energy expenditures were essentially fixed, and Dr. Caraco experimentally manipulated the expected daily energy intake of foraging birds. But competing theories predict similar behavior in these experiments. Dr. Caraco's new research involves studies for which the different theories predict different behaviors. He will hold expected daily energy intake constant and experimentally manipulate daily energy expenditures. Using walk-in coolers, he can select ambient temperatures where a ("warm-blooded") bird's food intake exceeds, equals, and falls short of its requirement. He anticipates that the bird's aversion to, or preference for, food-reward variability will still depend on a comparison of expected energy intake with expenditure. If Dr. Caraco's experimental results match his predictions, it would indicate that his theory provides a marked increase in our level of understanding of the behavioral strategies that promote survival in variable environments.