Designing effective reserve networks for nonequilibrium metacommunities

Abstract

The proliferation of efficient fishing practices has promoted the depletion of commercial stocks around the world and caused significant collateral damage to marine habitats. Recent empirical studies have shown that marine reserves can play an important role in reversing these effects. Equilibrium metapopulation models predict that networks of marine reserves can provide similar benefits so long as individual reserves are sufficiently large to achieve self-sustainability, or spaced based on the extent of dispersal of the target species in order to maintain connectivity between neighboring reserves. However, these guidelines have not been tested in nonequilibrium metacommunity models that exhibit the kinds of complex spatiotemporal dynamics typically seen in natural marine communities. Here, we used a spatially explicit predator–prey model whose predictions have been validated in a marine system to show that current guidelines are not optimal for metacommunities. In equilibrium metacommunities, there is a community-level trade-off for designing effective reserves: Networks whose size and spacing are smaller than the extent of dispersal maximize global predator abundance but minimize global prey abundance because of trophic cascades, whereas the converse is true for reserve networks whose size and spacing are larger than the extent of dispersal. In nonequilibrium metacommunities, reserves whose size and spacing match the extent of spatial autocorrelation in adult abundance (i.e., the extent of patchiness) escape this community-level trade-off by maximizing global abundance and persistence of both the prey and the predator. Overall, these results suggest that using the extent of adult patchiness instead of the extent of larval dispersal as the size and spacing of reserve networks is critical for designing community-based management strategies. By emphasizing patchiness over dispersal distance, our results show how the apparent complexity of nonequilibrium communities can actually simplify management guidelines and reduce uncertainty associated with the assessment of dispersal in marine environments.Keywords: metacommunities, dynamic resources, spatial management, patchiness, reserve networks, nonequilibrium, trophic cascade