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Population Dynamics of a Long-distance Migratory Insect

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Title: Population Dynamics of a Long-distance Migratory Insect
Author: Flockhart, David Thomas Tyler
Department: Department of Integrative Biology
Program: Integrative Biology
Advisor: Norris, RyanMartin, Tara
Abstract: The population dynamics of migratory animals requires understanding how individuals move, survive, and reproduce throughout the year. How sequential life history events interact to influence population abundance depends upon how populations are spatially connected, termed their migratory connectivity. Developing predictive models of population dynamics for these species requires integrating patterns of migratory connectivity and demographic population processes across the annual cycle. In this thesis, I used the the iconic monarch butterfly (Danaus plexippus) as a model to understand the population dynamics of long-distance migratory animals. In the first chapter, I geographically connected multiple breeding generations of monarch butterflies during an entire breeding season. Breeding monarchs moved north over successive generations but, by late summer, butterflies were moving south to breed. The implication is that monarchs have complex movement patterns over multiple breeding generations and multiple geographic locations are necessary to ensure population viability. In the second chapter, I experimentally measured density-dependent competition amongst larvae and adult monarch butterflies. Female butterflies did not lay fewer eggs under increasing density. However, larval mortality increased across a range of larval densities which correspond to densities commonly observed in field surveys in some geographic regions during the breeding season suggesting density dependence could operate dynamically in space and time across the breeding season. In the third chapter, I developed a stochastic, density-dependent population model that linked migratory connectivity and demographic vital rates across the annual cycle. I found that under continuing habitat loss and projected climate change scenarios, the monarch butterfly population will decline at such a rate that it will meet the IUCN criteria to be listed as vulnerable. In contrast to the traditional conservation focus on the wintering grounds, my results suggest that monarch population abundance is most sensitive to changes in vital rates on the breeding grounds. The results of these studies provide a model system where year-round population models can be used to quantify contributions to population growth across the annual cycle. Ultimately, developing structured quantitative models is a necessary prerequisite to formally address conservation decision-making for long-distance migratory animals at continental scales.
URI: http://hdl.handle.net/10214/7620
Date: 2013-11
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