Feeding under predation hazard: testing models of adaptive behavior with stream fish.

Many empirical studies support the premise that animals consider both the benefits of feeding and the cost of mortality when making behavioral decisions, and many theoretical studies predict animal behavior in the presence of a feeding-mortality trade-off. However, empirical work is lacking in studies that quantitatively assess alternative models. Using data from two sets of behavioral experiments examining stream minnows (bluehead chubs) foraging in the presence of sunfish predators (green sunfish), we assess, via statistical model fitting, the utility of four basic optimization models of foraging behavior. Our analysis of feeding and mortality of the minnows indicates that mortality is incurred so as to feed above maintenance requirements, that feeding rate is suppressed in response to the presence of predators, and that the balance of feeding against mortality can be estimated using a life-history parameter theta, interpreted theoretically as the marginal rate of substitution of mortality rate for growth rate. Our results indicate that both body size and age are probably involved in determining the value of theta, and we suggest that future studies should focus on estimating and understanding this parameter.