Demography and parental investment in orange-crowned warblers: testing life history theory

Abstract

Understanding the diversification of life history strategies is a major goal of evolutionary ecology. Research on avian life history strategies has historically focused on explaining variation in clutch size, and most studies have tested whether this variation can be explained by variation in a single ecological factor, such as food availability or mortality risk. However, relatively few studies have evaluated whether the causes of variation within populations are distinct from or similar to the causes of variation between populations. In my dissertation, I compare the life history strategies of orange-crowned warbler (Oreothlypis celata) populations and study the causes of variation in clutch sizes, incubation behavior, nestling provisioning rates, nestling growth rates, and breeding phenology. I tested alternative hypotheses for the ecological causes of divergent life histories, and assessed the consequences of these different reproductive strategies for parents and offspring. My results indicate that no single ecological factor can explain life history variation either within or between populations. Instead, life history and behavioral traits differ in their sensitivities to different ecological factors, and while differences between nearby populations can reflect plastic responses to ecological variation, populations that are more geographically and evolutionarily distant can differ in both their responses to ecological variation and in the consequences of variation in parental behavior for offspring growth and development.