The relationship between host species diversity and fitness of generalist parasites is underdeveloped, including cases of vector-borne parasite transmission where generalist-feeding vectors facilitate cross-species transmission in host communities that vary across space and time, generating hot spots and hot moments for parasite transmission. To explore this effect, we developed a tractable model for transmission dynamics which includes a host community of arbitrary richness along with a single vector species. To compare parasite fitness across communities, we calculated the basic reproductive ratio of the parasite (R0) in host communities of different composition. In particular, we develop results to compare sets of host communities to their subsets, which allows flexible scenario building, including loss of apex predators following habitat degradation, trophic cascades, and introduction of novel host species due to natural invasion or anthropogenic translocation. Additionally, we include a flexible approach whereby vector abundance can respond to changes in host abundance. We characterize plausible host communities via phenomenological relationships between host species abundance and competency, and evaluate how parasite transmission potential may respond to these common changes to host communities.
Results/Conclusions
Relative abundance of host species in the community strongly impacts parasite transmission, as does species competency and the potential response of vector abundance to community changes. When the invader host species is more competent for the parasite, increased fitness is possible. However, increased fitness can also occur when the invader species is less competent. A potential mechanism for decreased parasite fitness in higher richness host communities regardless of invader competency is bite reduction, which occurs when vector bites per host decrease. When host community disassembly is modeled as a trophic cascade, the change in parasite fitness is dependent on the current level of disassembly across the explored abundance-competency relationships. Overall, we have shown that increased host richness does not strictly result in decreased parasite fitness, even when the additional host species is less competent for the parasite.