Date of Award

Summer 7-2-2014

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Pieter Johnson

Second Advisor

Valerie McKenzie

Third Advisor

Kendi Davies

Abstract

Metacommunity theory investigates how local (species interactions and environmental filters) and regional (movement across the landscape) processes combine to determine the distribution, composition, and diversity of communities. In particular, studies of metacommunities usually explicitly or implicitly incorporate space, leading to an emphasis on spatial scale. Most metacommunity studies have focused on free-living organisms; however, using parasite communities offers unique insight into metacommunity patterns and processes through high replication and the ability to incorporate an additional scale. Complex life cycle parasite communities have three spatial scales that are biological important (1) within host, where parasite communities interact with each other and the host immune system, (2) within locality, where the host demography and environmental conditions can affect free-living parasite stage success, and (3) across the landscape, following the movement of their most vagile hosts, usually vertebrates. I used a metacommunity of flatworm (digenean trematode) parasites in their freshwater mollusk hosts to investigate metacommunity patterns and processes across scales.

I used a combination of broad field surveys, advanced statistics, mathematical models, and experimentation to evaluate how patterns and processes affecting metacommunities shifted across the spatial scale of investigation. Within hosts, I found that parasite communities can be interactive, affecting each other's colonization of host snails in controlled experimental mesocosms. Scaling up to within a locality, site and species specific feedbacks were more important than interspecific interactions based on a series of metacommunity models fit to a three year field dataset of a trematode metacommunity. On the same metacommunity scale, I investigated the relationship between avian hosts and trematode infections. I found that avian host use had strong seasonal patterns, and that trematode species richness and prevalence was positively related to the abundance and richness of birds. Then I scaled up again to consider patterns and processes affecting trematode metacommunities across the landscape using a two year field study. The availability of mollusk hosts was most important for landscape level trematode metacommunity structure. Overall, the drivers of parasite metacommunities shifted across scales, with interspecific interactions important within hosts, but with site level characteristics most important within sites and across the landscape.

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