Identifying mechanisms driving assembly of parasite communities within hosts

Background/Question/Methods

Hosts with multiple infections are ubiquitous in nature. However, much of the literature on parasite communities is descriptive rather than experimental, and so we do not have a good idea of what the important structuring mechanisms of parasite communities are. Luckily, parasite and traditional communities are similar enough that we can use community ecology concepts to understand parasite community assembly rules. In this study, we attempt to elucidate how differences in energy flow and patch dynamics between parasite communities and traditional communities alter the create new opportunities for parasite co-existance. We address this question primarily through a combination of numerical and individual based modeling. 

Results/Conclusions

Parasite communities are similar to traditional communities in that they have multilevel trophic interactions, with the immune system feeding on parasites, which feed on host resources. They also experience meta-community dynamics, with parasites dispersing between hosts, which act as patches. Additionally, parasite and traditional communities share many of the same structuring processes, such as niche differences, neutral processes, priority effects and environmental filtering. However, there are a few dissimilarities which cause key differences in how parasite communities are structured. First, energy in parasite communities does not flow up a food chain. Rather, the bottom and top tropic levels (within host resources and the immune system), are the same organism, and compete with the middle trophic level (parasites) for energy. Secondly, as parasites exert control over host population dynamics, parasite community structure will influence patch density dynamics, leading to complex feedbacks. Overall, these differences could lead to dynamics that cannot be explained by traditional ecology concepts, and will restructure the relative importance of community assembly rules, leading to parasites prioritizing different colonization strategies than organisms in a traditional community.