In the current crisis of biodiversity loss, species governed by metapopulation dynamics approaching extinction should become more and more common. Dispersal is a fundamental process in metapopulation dynamics. This work investigates the role of dispersal when a metapopulation approaches extinction. Here, we define extremity as set of conditions that threaten metapopulation persistence. We consider the three most common extremity drivers considered in classical metapopulation models about dispersal evolution: 1) off-patch mortality; 2) disturbance (frequency and intensity); 3) intra-patch density-dependence. We use a spatially implicit model in which ten clones varying in dispersal rates compete to persist in a metapopulation undergoing local disturbance. The model combines intra-patch dynamics with logistic growth, coupled by transience among patches mediated by the dispersal environment. The parameter values of the model are based on the biological context of a symbiont-host system (where hosts represent the patches).
Results/Conclusions
We demonstrate how competition acting on a gradient of available dispersal strategies explains the general predicted trends of increased evolutionary stable dispersal when system conditions approach extremity. We describe commonalities in abundance and occupancy patterns provoked by the different drivers of extremity, that explain the consistent positive effect of extremity on selected dispersal. Our study suggests that environmental changes can intensify extremity effects if their influence encompasses both intra-patch and dispersal environments. Furthermore, we demonstrate how increased dispersal under extreme conditions can help species to mitigate the effects of extremity through maximization of metapopulation size. Hence, increased dispersal is a potential rescue mechanism for species approaching extinction.