OPTIMAL TRAITS WHEN THERE ARE SEVERAL COSTS - THE INTERACTION OF MORTALITY AND ENERGY COSTS IN DETERMINING FORAGING BEHAVIOR

I analyzed the interaction of different types of costs in determining optimal behavior using mathematical models. The analysis concentrates on foraging behavior and asks (1) whether the cost factor that has the greatest effect on fitness generally has the greatest effect on optimal trait values and (2) whether increasing the size of one type of cost makes the optimal behavior absolutely or relatively more sensitive to that cost. The foraging costs considered are energy expenditure, predation risk, and other mortality factors. It is shown that increasing the magnitude of one cost often decreases the relative and absolute sensitivity of the optimal foraging strategy to that cost. The relative fitness effects of different costs generally differ from the relative sensitivities of the optimal strategies to the cost factors. Researchers should therefore measure the shapes of cost curves rather than their average magnitudes to determine which of several costs can be ignored in cost-benefit analyses.