Designing effective reserve networks for non-equilibrium metacommunities

Background/Question/Methods

The proliferation of efficient and destructive fishing practices has promoted the depletion of commercial stocks around the world and caused significant collateral damage to marine habitats and non-commercial species. Recent empirical studies have shown that marine reserves can serve both conservation and fishery management goals by protecting communities from collateral damage and promoting the abundance of depleted commercial species within and beyond their boundaries. Equilibrium models predict that networks of marine reserves can provide similar benefits so long as individual reserves are sufficiently large to retain subsidies and achieve self-sustainability, or spaced judiciously in order to maintain connectivity between neighboring reserves via spillover. However, the applicability of these guidelines has not been tested in non-equilibrium models despite the fact that marine populations typically exhibit strong variability in both time and space.

Results/Conclusions

Using a spatially-explicit predator-prey model whose predictions have been validated in a natural marine system, we show that current guidelines are optimal for equilibrium metacommunities but not for non-equilibrium metacommunities. In equilibrium metacommunities, there is a community-level tradeoff 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 non-equilibrium metacommunities, using the extent of dispersal as the size and spacing of reserves minimizes the persistence of both the predator and the prey, and introduces a similar community-level tradeoff: reserves characterized by small (large) size and spacing provide a mild increase (reduction) in global predator abundance and minimize (maximize) global prey abundance. When the size and spacing of reserves matches the extent of naturally-occurring patterns of abundance (i.e., patchiness), this community-level tradeoff disappears as global abundance and persistence of both the prey and the predator are maximized. Overall, these results suggest that using the extent of patchiness instead of the extent of dispersal as the size and spacing of reserve networks is critical for designing effective, community-level management strategies that maximize the abundance and persistence of dynamic and trophically-coupled resources.