Whether populations are sustained primarily by immigrants (open) or by self-recruitment (closed) remains one of the largest mysteries in marine ecology. Unraveling this mystery is critically important for deciding whether conservation should occur at regional or local scales. Previous research has revealed both high levels of long-distance gene flow (suggesting open populations) and high levels of self-recruitment (suggesting closed populations), even for species with nearly identical life histories. Here, we show how metapopulation theory and greater attention to habitat patchiness can explain this apparent contradiction.
Results/Conclusions
We first develop simple models for population openness as a function of habitat size and spacing. We then show that closed populations (high self-recruitment) can arise from small changes in habitat spacing, particularly when spacing is close to twice the dispersal distance. This finding suggests that observations of self-recruitment do not require unusually short dispersal distances. We apply the model to two maps of coral reefs to demonstrate that typical marine habitats likely create a patchwork of open and closed populations across the seascape. Finally, we apply the model to 17 coral seascapes from around the world to show that habitat patchiness varies substantially from region to region. Those landscapes with larger habitat gaps are predicted to contain closed populations for more species. The variability we discover appears sufficient to explain why previous research has uncovered both long-distance dispersal and closed populations, implying that such observations are not as contradictory as previously thought. Our work suggests that greater attention to habitat configuration in marine environments will improve our understanding of dispersal across a wide range of species. Our model may also provide a simple method for incorporating dispersal knowledge into conservation decisions in areas where detailed information is otherwise lacking.