Synchronous population dynamics can reduce the persistence of spatial population networks. Thus understanding factors that affect synchrony are important from both basic and applied perspectives. Synchrony is generally thought to arise through either dispersal among populations or exogenous forcing by density-dependent or density-independent factors. I explored an additional mechanism - that the simultaneous loss or gain of immigrants resulting from local extinction and recolonization may synchronize populations through internal pulsed forcing. Using simulation modeling of eight logistic populations, I explored conditions under which extinction and colonization can affect synchrony. I was particularly interested in how differences in dispersal and heterogeneity among populations in carrying capacity affect synchrony following extinction or recolonization.
Results/Conclusions
Both local extinction and colonization affect synchrony. For homogeneous populations, a decrease in immigration resulting from local extinction decreases synchrony, while an increase in immigration from recolonization increases synchrony. For heterogeneous populations results were more complex. Both extinction and recolonization could either increase or decrease synchrony depending population growth rates, dispersal rates, the pattern of dispersal among populations and the size of populations undergoing extinction or recolonization relative to other populations. The results indicate that both local extinction and recolonization can create a positive feedback increasing the risk of extinction for the entire network. These effects were greatest for networks of populations with high dispersal rates. The results also imply that stochastic patch occupancy models (SPOMs), which do not account for local dynamics, underestimate the risk of metapopulation extinction.
