| The search for fundamental patterns or rules by which parasites establish and persist in free-living species is a rapidly expanding area of interest for both parasitologists and ecologists. Though host-parasite interactions are fairly well understood at the population level, little is known about parasitism at the community level, nor why some free-living species harbor many parasite taxa while others are seemingly resistant to parasite establishment. The purpose of this dissertation was to explore several species and community attributes that could be important to parasite establishment and persistence in both a marine saltmarsh (Tuckerton, NJ) and a freshwater riverine system (Raritan River, NJ). This study specifically emphasized feeding interactions, abundance and spatial distributions of free-living species and their respective helminth parasites. In Tuckerton saltmarsh, I observed a strong spatial patterning in trematode infections of the mudsnail, Ilyanassa obsoleta, and this pattern is strongly correlated with habitat type and host quality. At the community level (along with data from four previously published systems), trophically transmitted parasites were found to utilize asymmetric predator-prey interactions, in which predator hosts have many prey items and prey hosts have relatively few predators. In a pristine site along the Raritan River high resolution abundance data revealed that predator-prey interactions are spatially constrained by habitat and that this pattern was even stronger for host-host and parasite-host interactions. Finally, I found a decrease in efficiency of biomass transfer up trophic levels across a perturbation gradient in this river system. This pattern correlated with losses in both free-living and parasite diversity. However, the relationship between these factors and human impact was not linear, suggesting a threshold at which community structure becomes less invasible by parasites. Collectively, this study suggests that spatial context, in combination with community structure, can greatly affect parasite establishment and persistence and can be used to explain or predict which free-living species are more hospitable hosts. |
