Runaway Dispersal in Social Species
Local populations are in most cases open and connected with other populations through dispersal. Dispersal, aside from its multiplicative nature, has a demographic additive effect for the spatiotemporal dynamics and extinction–colonization turnover of the donor and the receiver populations. Population dynamics are more sensitive to dispersal under perturbations, because dispersing is a resilience mechanism to avoid or reduce novel mortality risk. Furthermore, dispersing individuals carry information, a process that may create dynamic landscape information networks. In social species, the decision to stay or to disperse is made based on decisions made by others. When perturbations accumulate and jeopardize survival or fecundity, leading individuals may decide to disperse, and this decision is copied by others, generating a runaway dispersal to other patches. The decision trade-off between staying and dispersing depends on the dynamic spatiotemporal heterogeneity in patch quality. What matters for making a decision is not the difference in patch quality, but the ratio between the patch currently occupied and the rest of the patches. Decision-making in social animals for dispersing is explored under the frameworks of the prospect theory, the neoclassical economic theory, and the hypercycle theory. It is also shown how runaway dispersal may occur from a theoretical point of view due to a very simple mechanism of copying others in a density-dependent manner. This simple mechanism overruns a rational scenario when making decisions in social animals. This chapter ends by assessing the potential consequences of runaway dispersal for nonlinear responses in communities and entire ecosystems.