Metapopulations persist when local populations are rapidly recolonized following local extinctions. Such persistence requires asynchrony; simultaneous crashes of all populations would leave no source for recolonization. Previous work shows theoretically and experimentally that population extinctions due to severe disturbances can promote metapopulation persistence by preventing spatial synchrony, thereby enhancing recolonization. This behavior is termed the ‘spatial hydra effect’: extinctions can increase recolonization, analogous to how the mythical hydra grew two new heads when one was cut off. But many local populations go extinct due to their own dynamics, as when a disease fades out locally after exhausting the local population of susceptible hosts, or when a small local population goes extinct due to demographic stochasticity. Can such “self-generated” local extinctions promote metapopulation persistence via a spatial hydra effect? The answer is unclear, because "self-generated" local extinctions might be correlated in space and time, in ways that prevent them from enhancing recolonization.
Results/Conclusions
I simulated three different metapopulation models to identify conditions under which "self-generated" local extinctions promote metapopulation persistence. Self-generated local extinctions promote metapopulation persistence in a stochastic spatial version of the Nicholson-Bailey parasitoid-host model, but not in a stochastic spatial version of the Rosenzweig-MacArthur predator-prey model. The differing behaviors of the parasitoid-host and predator-prey models apparently arise because local extinctions reduce rescue effects in the predator-prey model, but not in the parasitoid-host model. Self-generated local extinctions also can promote metapopulation persistence in a realistic, spatially-explicit model of a rare New Zealand weevil and its plant host, indicating that metapopulation persistence via a “self-generated” spatial hydra effect is a real world possibility and not merely a theoretical curiosity. Some metapopulations may depend on local extinctions for their persistence, rather than being threatened by them. Persistence via a self-generated spatial hydra effects seems most likely in metapopulations with dynamics that doom them to local extinction, as with some specialized consumers and diseases.