Adaptive behavior and interference in the functional response of predator to prey

Behavior plays a central role in predator-prey interactions. Moreover, most animals occupy intermediate positions in food webs and must acquire resources for growth and reproduction while simultaneously avoiding predation mortality. This dissertation explores quantitative methods for conceptualizing the behavior of individuals that are predators, prey or both.; Chapter 1 is a theoretical study of the behavior of animals facing a three-way tradeoff among rates of growth, mortality and reproduction: improvements in one of these components of Darwinian fitness can only be obtained at the expense of the remaining two components. Dynamic optimization and ideal-free distribution theory are applied to predict that non-growing adults should behave so as to minimize the ratio of mortality rate to birth rate and that mortality rate should be linear in rates of growth and reproduction when measured across habitat patches. A literature review identifies challenges in testing the theory.; Chapter 2 is a statistical evaluation of four functional response models using 19 data sets from the literature. The classic prey-dependent functional response (a functional response depending on prey abundance alone), the Holling Type II model, can be rejected in 18 of the 19 data sets because one of three predator-dependent forms (a functional response depending on prey and predator abundance) provides a statistically better fit to the data. Data sets indicating predator-dependence at high prey abundances favor the Crowley-Martin model, whereas models lacking such predator-dependence favor the Beddington-DeAngelis and Hassell-Varley forms.; Chapter 3 presents the results of laboratory tests of four alternative optimization models of behavior: maximize growth, minimize mortality, minimize mortality/growth and maximize a linear combination of growth and mortality. The feeding and mortality rates of stream minnows measured in the presence of varying amounts of food and green sunfish predators are used with statistical model fitting to evaluate the models. The minnows behaved so as to balance growth and mortality and their assessment of the growth-mortality tradeoff can be quantitatively estimated in terms of reproductive value.