Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Pieter T.J. Johnson

Second Advisor

Andrew Martin

Third Advisor

Samuel Flaxman

Fourth Advisor

Christy McCain

Fifth Advisor

Robert Garcea

Abstract

In wildlife communities, the diversity of both host species and pathogens can affect disease and transmission dynamics. However, the various mechanisms leading to these biodiversity effects occur at strikingly different spatial scales. For my dissertation, I used empirical and theoretical tools to understand how pathogen and host diversity affect transmission at multiple scales. First, I conducted a series of laboratory experiments using a genus of viruses, Ranavirus, which can cause devastating die-offs in amphibian populations. I asked how multiple virus types might interact to affect individual-level probabilities of infection and, subsequently, population-level transmission dynamics. I found that co-exposure to two Ranavirus species substantially increased the probability of an amphibian larva becoming infected, as well as the average viral load among individuals. Concordantly, the presence of multiple Ranavirus species led to larger epidemics in experimental populations, as well as an increased probability of mortality. This research illustrates that Ranavirus coinfection could strongly mediate epidemic dynamics in natural amphibian populations. In the next part of my dissertation, I created an epidemiological model in which a single pathogen circulates through a vertebrate host community. I found that the relationship between host species richness and pathogen transmission could be positive, negative, or non-monotonic depending on how the host's total community density scales with host richness and the type of pathogen transmission assumed. These results highlight that host community composition influences transmission in complex ways, suggesting that observing a consistent effect of host diversity in natural systems is unlikely. Finally, scaling up and using a metacommunity framework, I developed a statistical method to explore how symbiont (including pathogen) communities are structured across space. I then applied this method to a large scale, longitudinal data set of amphibian symbiont communities and discovered that the structure of these communities changes through time and is predominantly influenced by temporal changes in host community composition. Overall, my research illustrates that transmission dynamics are influenced by factors at multiple spatial scales and that integrating across scales is important for understanding how, where, and when biodiversity will affect disease dynamics.

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