Year of Award

2020

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

L. Scott Mills

Commitee Members

Jedediah F. Brodie, Paul M. Lukacs, Thomas E. Martin, Kevin S. McKelvey

Keywords

cycle dampening, density, population cycles, population dynamics, snowshoe hare, state space model

Publisher

University of Montana

Abstract

Although periodic fluctuations in species abundance have long fascinated society (e.g. lemming mass migrations and locust plagues in Egypt), it was not until 1924 that Charles Elton brought cycles to the attention of the scientific community. Following his work, cycle dynamics have remained an enigmatic area of ecology with many cyclic species exhibiting dampened and even acyclic dynamics across space (i.e. portions of their range) or time. One such species, snowshoe hares, exhibit drastic population fluctuations in the northern boreal, but are thought to exhibit dampened cyclic or acyclic population dynamics in the southern portion of their range with quantification hampered by lack of data. For my dissertation, I contrasted multiple biotic and abiotic drivers of hare population dynamics and quantified the cyclic nature of hare population fluctuations in Montana using a novel 21 year dataset and a rigorous modeling framework. I first directly estimated hare densities over space and time with a spatially-explicit capture-mark-recapture model. I then removed the measurement error component to focus on drivers of process variance in hare densities using a Bayesian state space model. I found support for hare population dynamics driven by landscapes with more open areas, greater generalist predation and warmer temperatures. Consistent with other studies, I found that increasing camouflage mismatch resulting from shorter snow duration lowers hare density. I also found that less frequent cold winter days increase density while hotter summers lower density with the future negative effect of warming summers likely overwhelming the future positive effect of reductions of cold winter days. Both increased generalist predation and more open landscapes were associated with lower hare densities supporting the generalist predation and landscape structure hypotheses. Finally, using four different cyclicity metrics, I concluded that Montana hares are acyclic. Thus, multiple drivers act simultaneously to produce acyclic dynamics emphasizing the need to apply a unified modeling framework which considers multiple drivers to other cyclic systems in order to better elucidate cycle dynamics.

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© Copyright 2020 Alexander Vishvamitra Kumar