Metacommunity size and functional diversity in a natural mesocosm landscape

Background/Question/Methods

Ecosystems are often arranged in naturally patchy landscapes with habitat patches linked by dispersal of species in a metacommunity. The size of a metacommunity, or number of patches, is predicted to influence community dynamics and therefore the structure and function of local communities. For example, species richness and evenness are expected to decrease with number of patches in a metacommunity while stochastic processes will increase. However, such predictions have yet to be experimentally tested using full food webs in natural metacommunities. We used the natural mesocosm system of aquatic macroinvertebrates in bromeliad phytotelmata to test the effect of the number of patches in a metacommunity on species richness, abundance, and community composition in a long term enclosure experiment.

Results/Conclusions

We found that species richness, abundance, and biomass were lower in enclosures compared to surrounding unenclosed bromeliads, but did not differ between enclosed metacommunities of differing patch numbers. Species diversity and evenness, however, significantly increased with increasing metacommunity size, with the smallest metacommunities showing greater stochasticity in community structure. Community composition was affected by metacommunity size with a greater predator to prey ratio in smaller metacommunities, and a more even detritivore community in larger metacommunities. Species-specific effects were predictable based on species traits. Our study is the first test of metacommunity size in a natural metacommunity landscape and shows that both diversity and community composition are significantly affected by metacommunity size. This study opens the door for more explicit tests of the mechanisms driving community change and ecosystem function in fragmented metacommunities.