Experimental insight into the process of parasite community assembly

Community assembly is a fundamental process that has long been a central focus in ecology. Extending community assembly theory to communities of co-infecting parasites, we used a gastrointestinal nematode removal experiment in free-ranging African buffalo to examine the community assembly patterns and processes. We first asked whether reassembled communities differ from undisturbed communities by comparing anthelmintic-treated and control hosts. Next, we examined the temporal dynamics of assembly using a cross-section of communities that reassembled for different periods of time since last experimental removal. Next, we tested for evidence of assembly processes that might drive such reassembly patterns: environmental filtering based on host traits (i.e. habitat patches), interspecific interactions, priority effects and chance dispersal from the environmental pool of infective stages (i.e. the regional species pool). On average, reassembled parasite communities had lower abundance, but were more diverse and even, and these patterns varied tightly with reassembly time. Over time, the communities within treated hosts progressively resembled controls as diversity and evenness decreased, while total abundance increased. Notably, experimental removal allowed us to attribute observed differences in abundance, diversity and evenness to the process of community assembly. During early reassembly, parasite accumulation was biased towards a subordinate species and, by excluding stochastic assembly processes (i.e. chance dispersal and priority effects), we were able to determine that early assembly is deterministic. Later in the reassembly process, we established that host traits, as well as stochastic dispersal from the environmental pool of infective stages, can affect the community composition. Overall, our results suggest that there is a high degree of resiliency and environmental dependence to the worm communities of buffalo. More generally, our data show that both deterministic and stochastic processes may play a role in the assembly of parasite communities of wild hosts, but their relative importance may vary temporally. Consequently, the best strategy for managing reassembling parasite communities may also need to shift over time.