Individual Heterogeneity in Ecology and Evolution
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Authors
Forsythe, Amy
Date
Type
thesis
Language
eng
Keyword
Population dynamics , Life-history theory , Vital rates , Individual heterogeneity , Population growth rate , Matrix population models , Fixed condition , Dynamic condition , Life-history trade-offs , Positive life-history covariances , Individual stochasticity
Alternative Title
Abstract
Among-individual variation in vital rates, such as mortality rates and birth rates, can generate substantial diversity across individual life histories that scales up to influence population-level processes. The effects of this individual heterogeneity on population growth rates are of particular interest because ecological and evolutionary dynamics, such as rates of extinction and rates of evolution, depend directly on population growth rates. Current research suggests that population growth rates differ in the presence versus absence of individual heterogeneity, however the population-level consequences of different types of individual heterogeneity are still largely unknown. Here, I develop a mathematical model to explore how different types of individual heterogeneity affect population growth rates in age-structured populations. I first present my findings from a thorough literature review, which reveals inconsistencies and ambiguities in the use of terminology surrounding individual heterogeneity. More than just an issue in semantics, these discrepancies highlight the need for a conceptual framework to bridge empirical and theoretical studies. Therefore, I synthesize previous approaches into a comprehensive framework of individual heterogeneity with explicit terminology and definitions. I establish a novel distinction between prospective vital rates and realized vital rates, which forms the basis for a framework with precise translations to mathematical models of individual heterogeneity. The framework further separates individual heterogeneity in which prospective vital rates are permanent ("fixed condition") or can change ("dynamic condition") throughout life. Subsequently, I apply this conceptual framework to develop age-structured models that compare population growth rates when individual life histories are structured as fixed versus dynamic condition. I find that except for rare cases, the type of individual heterogeneity influences population growth rates and the average contributions of each age class to overall population growth. I also show that heterogeneity can affect population growth rates in ways that depend on the sign of the covariance among prospective survival probabilities and birth rates. These results emphasize the importance of considering individual heterogeneity and its different structures when making predictions about population growth rates. Moreover, their divergent effects on population growth rates imply that fixed and dynamic condition can have distinct consequences for ecological and evolutionary processes.
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Copying and Preserving Your Thesis
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ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.