Unintended consequences: Adaptation to habitat loss may increase the likelihood of species extinction when accompanied by habitat fragmentation or environmental fluctuations

Background/Question/Methods

The ability of a species to disperse across a landscape has many important ecological consequences. Perhaps most pressing, dispersal allows species to shift ranges in response to climate change, habitat loss, or biological invasions. The evolutionary optimal dispersal rate is predicted to increase in response to increased local extinction, allowing locally unstable populations to persist regionally through re-colonization of recently extinct habitat patches. However, high dispersal can also synchronize local population dynamics, increasing the likelihood of synchronous extinction and metapopulation collapse. Synchrony can also be induced by environmental fluctuations. Thus, a critical question is: when are the selective benefits of dispersal in response to increased local extinction counteracted by the negative effects of synchrony? Dispersal, local extinction, and synchrony are all likely to have the strongest influence on metapopulations of predators and their prey. Predator-prey interactions tend to be locally unstable, and synchrony is amplified in the presence of predators. Using stochastic simulations of predator-prey interactions I measure metapopulation persistence as a function of local extinction (habitat patch size), synchrony (habitat patch number and environmental drivers), and dispersal.

Results/Conclusions

The model confirms the expectation that in the absence of synchrony, as local extinction increases (through reduced local patch size), metapopulation persistence is maximized at the predicted evolutionary optimal dispersal rate. However, if dispersal also tends to synchronize populations (through increased habitat patch number), then for high local extinction rates, metapopulation persistence is maximized at a dispersal rate less than the evolutionary optimum. The same is true if populations are additionally synchronized by environmental fluctuations. However, in the latter case metapopulation persistence approaches 0 for all dispersal rates as local extinction increases. The implications of these results are significant in an era where species are experiencing accelerating environmental changes like habitat loss (akin to decreased patch size) and fragmentation (akin to increased patch number) and increased environmental variability. The focus of many studies has been whether or not species can adapt quickly enough to respond to these types of disturbances. I suggest here that even if species are able to respond to increasing habitat loss, dispersal- or environmentally- mediated synchrony will counter the benefit of increased dispersal, driving the species to global extirpation regardless of their ability to adapt.