Novel parasite invasion leads to rapid demographic compensation and recovery in an experimental population of guppies

The global movement of pathogens is altering populations and communities through a variety of direct and indirect ecological pathways.  The direct effect of a pathogen on a host is reduced survival, which can lead to decreased population densities. However, theory also suggests that increased mortality can lead to no change or even increases in the density of the host. This paradoxical result can occur in a regulated population when the pathogen’s negative effect on survival is countered by increased reproduction at the lower density.  Here we analyze data from a long-term capture-mark-recapture experiment of Trinidadian guppies (Poecilia reticulata) that was recently infected with a nematode parasite (Camallanus cotti). By comparing the newly infected population with a control population that was not infected we show that decreases in the density of the infected guppy population were transient. The guppy population compensated for the decreased survival by a density-dependent increase ...