Protected areas are a key conservation strategy in both the terrestrial and marine realms, and are thought to protect biodiversity by reducing habitat loss and mortality due to harvesting. At the community level, increased abundance, biomass and diversity often follow protection, however the pathways to increased diversity are not well understood. For example, responses to protection in marine reserves often depend on species’ vulnerability to fishing pressure, and species richness may increase in protected areas due simply to increases in the numbers of individuals of species targeted by fishing (i.e., a sampling effect). An increase in the abundance of large predatory fishes in protected areas may also cause changes to trophic interactions, likely resulting in altered species abundance distributions (e.g., evenness) that can affect species richness within protected areas. Additionally, protected areas are a spatially explicit conservation strategy that imposes a management scale on top of the natural spatial scale of ecological processes, making scale-dependent assessments of biodiversity a priority for adaptive management. Here we combine different types of rarefaction (individual-, sample-based, and spatially-explicit) to attribute observed changes in richness in Mediterranean marine protected areas to changes in total and relative abundance of species.
Results/Conclusions
The effect of protected areas on species richness depends on species’ vulnerability to fishing and scale. Species with high vulnerability to fishing have higher densities of individuals in protected areas at all scales. This increased total abundance contributes to increased species richness in protected areas at small to intermediate scales, but it is the continued accumulation of rare species that dominates the increased richness found for highly vulnerable species at large scales. Additionally, the increased abundance of large predatory fishes is likely responsible for the increased evenness among species with low vulnerability to fishing at small to intermediate scales, due to predation of numerically dominant species. This increased evenness of low vulnerability fishes also contributes to large increases in richness at small to intermediate scales. But this effect of evenness on richness diminishes at large scales, however, and there is no difference in richness for these low vulnerability species at the scale of the Mediterranean. Our scale-sensitive analysis of how diversity components contribute to biodiversity changes in protected areas shows that altered species abundance distributions, and not increases in total abundance, dominate the effects of protection from fishing on the biodiversity of fishes in the Mediterranean.