Parasites are increasingly recognized as essential components in ecological communities. Hosts and parasites experience intimate, long-lasting associations that impact where they are found in space and how they interact in the larger ecological community. The spatial ecology of parasites is therefore an interesting and complex area of research that requires careful study. In this dissertation I explore three areas of parasite spatial ecology building on some of the latest statistical and mathematical tools in ecology. Specifically, I concentrate on a guild of trematodes in estuaries along the Pacific west coast. I begin by quantifying how parasite distributions vary across space, with special consideration of how to do so when parasite data is limited or affected by error. In the second chapter, I explore how to statistically predict trematode abundance across several estuaries and what these findings suggest about the mechanisms driving parasite abundance. Finally, I define a mathematical model describing host-parasite transmission dynamics in systems that demonstrate an encounter dilution effect as a result of infective stage depletion in the environment. These three works not only improve what is known about the focal trematode guild, but they also improve understanding of how statistical and mathematical models can be used to gain valuable, accurate insight about parasites more generally.

The biogeography of host-parasite dynamics is an area that has received little attention in studies of island ecology. While a few studies have shed insight on patterns of parasitism in insular host populations, more empirical evidence is needed to ascertain how isolation impacts parasites. Biogeography generally theorizes that the physical size of islands and the duration of each island’s isolation can be driving geographic factors controlling species interactions and populations dynamics. To test this, we assessed the effect of island structure and population isolation on the endemic insular lizard Podarcis erhardii and its native hemogregarine parasite (Apicomplexa: Adeleorina) in the Cyclades (Aegean Sea). We analyzed the relationships of prevalence and parasitemia of hemogregarine infection with several factors concerning the island (size, time of isolation, spatial isolation, population density) and host (body size) levels using regression and structural equation models, respectively. Regressions indicate that islands with greater host density and islands which have been isolated for shorter timespans tend to have higher hemogregarine prevalences; structural equation models suggest a similar pattern for parasitemia. We hypothesize this may be driven by insular density compensation. Hosts on islands that are more temporally and spatially isolated also tend to have higher prevalence and parasitemia of hemogregarines. Our results indicate that island area, island isolation, and host population density are likely to be significant drivers of changes in host-parasite interactions in fragmented populations.