LB 23-248 - Optimal parasite strategies on disturbed island habitats connected by dispersal

Background/Question/Methods:

Parasites rely on hosts, which are island-like, ephemeral resources. Hosts, in turn, often live in metapopulations – distributed among discrete habitat patches connected by dispersal and subject to local extinction events due to habitat disturbance. Parasites may be more vulnerable to habitat disturbance than their hosts since they are affected both directly, through increased mortality, and indirectly, through reduced host density (which reduces transmission). Parasites also impact their host by increasing mortality or eliminating reproduction (castration), leading to potential tradeoffs in parasite strategies as disturbance intensifies. Here, we address the question: How do parasite colonization potential (good colonizer versus poor colonizer) and mode of host impact (increasing mortality versus castration) interact to influence occupancy and persistence under different disturbance scenarios? We address this question using a discrete-time, stochastic, cellular automaton model. The model tracks changes in parasite occupancy (number of habitable cells occupied) in networks of habitat patches connected by dispersal, both on individual patches and at the landscape-level.

Results/Conclusions:

In our model, when disturbance was infrequent, parasites reach the highest occupancy by being poorer colonizers while minimizing their impact on hosts. As disturbance frequency increases, parasites achieve higher occupancy by being increasingly better colonizers, even at the expense of harming their hosts more. Castrators have greater occupancy under all disturbance frequencies and persist under higher disturbance frequencies than parasites that increase mortality. On individual islands, the time until parasite recolonization and the time to reach equilibrium after disturbance are not heavily influenced by the parasite’s colonization ability or mode of host impact; rather, these rates depend more on the disturbance frequency and colonization status of neighboring islands. These results help interpret observations that some types of parasite species are more successful than others in isolated, disturbed habitats. Specifically, parasites that castrate their host rather than causing mortality, or parasites with strategies for rapid reproduction and colonization even at the cost of increasing host mortality, will persist under higher disturbance frequencies and reach higher densities in disturbed metapopulations.