Factors structuring parasite communities: testing alternatives to distance decay

Grant Winners

Dean

Abstract

Parasites are ubiquitous components of all major ecosystems, but the biogeographical factors that determine parasite species richness and community composition remain poorly studied. Previous studies have explored how processes operating at different scales (local, landscape, ecosystem) shape parasite communities; one commonly-tested factor is distance decay. In Biogeography, distance decay refers to a decrease of similarity between two biological communities as the distance between them increases. Theoretically, this negative relationship between distance and similarity is driven by species turnover along environmental gradients. Although distance decay has been demonstrated in free-living organisms, its application to parasite biogeography is problematic because a) significant distance decay effects are rarely observed in parasite communities, and b) observations of distance decay fail to provide information on the nature of the environmental gradients that are actually shaping the communities. We propose to critically assess the application of distance decay to parasite biogeography using 1) a field study of the parasite communities of fishes in the genus Fundulus, followed by 2) quantitative meta-analysis of published accounts of parasite community structure. We focus our field work on Fundulus (killifishes and topminnows) because they are excellent models to study parasite communities across a large geographic range: they host diverse parasite communities, and vary in their preferred habitats, allowing us to study how abiotic factors such as latitude, climate, landscape use, and water chemistry shape parasite community composition among closely related fishes. We will combine published and archival parasite data on Fundulus spp. with field data to compare the effect size of the above factors (including distance decay) in shaping parasite communities in Fundulus spp. For the second phase of this study, we will use a quantitative meta-analysis to test whether the conclusions of our field data are generalizable to parasite communities in other hosts. Using standard data mining techniques to extract information on latitude, longitude, parasite community species richness, and site-specific abiotic factors (latitude, Köppen Climate Classification, landscape use, salinity, …), we will calculate the effect size (as ohen's f2 = r2 / (1 - r2)) associated with each factor, as well as that for distance; we will then compare these effect sizes statistically. This project will provide a much-needed critical assessment of distance decay as a surrogate measure of environmental gradients in parasite biogeography, and consider alternative factors, such as temperature (climate) or landscape use, that are likely playing a more direct, quantifiable role in shaping parasite communities.