The cost of protecting biodiversity in harvested metacommunities

Background/Question/Methods

Marine reserves are often established with the goal of protecting biodiversity.  It is regularly assumed that this protection must result in reduced economic productivity.  Quantifying this tradeoff requires spatial models that include many interacting species as well as the effects of harvesting on both the biological community and on profit.  However, for mathematical tractability, previous work has almost exclusively focused on models with only one or two species.  We have constructed and analyzed metacommunity models to investigate the tradeoff between profits and biodiversity in harvested systems with an arbitrary number of species.  To explore how species interactions can influence the tradeoff, we compare communities that are assembled either as a result of colonization by independent species that do not interact, or as a result of ecological succession (i.e. obligatory facilitation). In addition, we compare the balance between biodiversity and profit under traditional (effort-based) management or by using marine reserves.

Results/Conclusions

In our models, species diversity decreases monotonically with harvesting effort, while profits are maximized at an intermediate level of harvesting.  As a result, there is always some cost (in terms of forgone profits) for maximizing diversity.  At the same time, there is always a diversity cost associated with maximizing profit. This diversity cost is more sensitive to economic parameters in successional communities than in communities with independent species. Furthermore, incorrectly ignoring species interactions when they are present can result in diversity lower by approximately 75% relative to the successional profit-maximizing value. When species interactions are incorrectly ignored, profits can drop as drastically, with profits over three times lower. The establishment of spatial reserves always results in a reduction in potential profits (compared with traditional management), but results in higher diversity.  In overharvested systems, diversity and economic productivity can simultaneously improve by reducing effort.