Aggregation begets aggregation: spatial distribution of environmental
parasites shapes parasite aggregation on host populations, but only at
low-to-moderate parasite density
Abstract
Spatial aggregation of environmental or trophically transmitted
parasites has the potential to influence host-parasite interactions. The
distribution of parasites on hosts is one result of those interactions,
and the role of spatial aggregation relative to intrinsic host factors
is unclear. We use a spatially explicit agent-based model to determine
how spatial aggregation of parasites influences the distribution of
parasite burdens across a range of parasite densities and host recovery
rates. Our model simulates the random movement of hosts across
landscapes with varying spatial configurations of areas infested by
environmental parasites, allowing hosts to acquire parasites they
encounter and subsequently recover from them. When parasites are more
spatially aggregated in the environment, the aggregation of parasite
burdens on hosts is higher (i.e., more hosts with few parasites, fewer
hosts with many parasites), but the effect is less pronounced at high
parasite density and fast host recovery rates. In addition, the
correlation between individual hosts’ final parasite burdens and their
cumulative parasite burdens (including lost parasites) is greater at
higher levels of spatial parasite aggregation. Our work suggests that
fine-scale spatial patterns of parasites can play a strong role in
shaping how hosts are parasitized, particularly when parasite density is
low-to-moderate and recovery rates are slow.