The influence of isolation on the dynamics of populations and communities

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Calabrese, Justin
Fagan, William F
Isolation is defined as the separation in time or space of individuals, populations, or of species within a community. Though isolation can be the result of many ecological processes, its role in affecting the structure and dynamics of populations and communities is not often acknowledged directly. For example, spatial heterogeneity is a frequently recognized as a significant ecological factor, but the effects of spatial heterogeneity are manifested through the isolation that heterogeneity imposes on the focal populations or communities. Isolation is an important, but hidden, component of many other ecological theories and frameworks as well. In this dissertation, I explore the role of isolation per se as an organizing theme in ecology by studying the effects of isolation in time and in space on both populations and communities. Chapter 1 explores how isolation in time among individuals in a population may affect the population's dynamics and risk of extinction. Through a combination of modeling and meta-analysis, Chapter 1 demonstrates that reproductive asynchrony, a form of temporal isolation, can have profound negative effects at the population level in species that feature annual lifecycles. Chapter 2 reviews and synthesizes the literature on habitat connectivity, the inverse of spatial isolation, and lays out a novel framework for organizing and understanding the different metrics used to measure the connectivity. Chapter 3 examines the role of spatial isolation among species in an assemblage of Costa Rican bark beetles in mediating species interactions. The chapter uses a combination of modeling and field-collected observational data to test the hypothesis that isolation among species in this bark beetle assemblage results in a community that behaves neutrally. The studies presented in this dissertation represent a broad sweep of the ways in which the concept of isolation may be applied to better understand the dynamics of populations and communities. Individually, each chapter is an original contribution to the ecology literature. Taken together, these papers demonstrate the power of isolation as an organizing theme in ecology and will hopefully stimulate increased research effort and theoretical development around the concept of isolation.