UC Davis

Anthropogenic environmental changes have dramatically impacted natural populations. Phenotypic responses represent a key set of mechanisms by which organisms cope with these environmental changes. Some species have responded well and proliferated, while most have responded poorly and declined. Success depends both on the evolutionary pressures that shape a population’s phenotypic strategies, as well as contingent events as population responds to a particular change. This dissertation develops theory to better understand the role of both past evolution and contingency on the ability of populations to cope with rapid environmental change. My first chapter models the influence of variability in seed fall on the evolution of caching behavior in scatterhoarding rodents, with parameters derived from the European beech (Fagus sylvatica) and yellow-necked mice (Apodemus flavicollis). We find that caching behavior is more prevalent when seed fall is more variable, illustrating the importance of environmental variability in driving phenotypic evolution. My second chapter models the evolution of within-generational plasticity, transgenerational plasticity, and bet-hedging as part of a unified “cue integration system” under a range of historical environmental conditions. We examine how different cue integration systems affect populations’ ability to cope with multiple types of environmental change, finding that populations tend to cope poorly when environmental change makes previously reliable cues unreliable. This chapter ties together the effect of historical conditions on the evolution of phenotypic strategies and the ability of those evolved strategies to enable a population to respond to a changing environment. My third chapter models how different kinds of contingency, in the form of demographic stochasticity, sex-ratio stochasticity, and phenotypic stochasticity, affect the likelihood of extinction for a population that must rapidly adapt to a changing environment in order to persist. I find that phenotypic stochasticity contributes relatively more to the ability to predict extinction or recovery than demographic stochasticity or sex ratio stochasticity early during rescue but contributes less as time goes on. Taken together, these chapters tie together the effects of evolutionary history and stochastic contingency on populations’ ability to respond to environmental change and make important progress in understanding the complex ways in which anthropogenic change affects the natural world.