Metacommunity size influences aquatic community composition in a natural mesocosm landscape (original) (raw)

Ecosystems are often arranged in naturally patchy landscapes with habitat patches linked by dispersal of species in a metacommunity. Th e size of a metacommunity, or number of patches, is predicted to infl uence community dynamics and therefore the structure and function of local communities. 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 eff ect of the number of patches in a metacommunity on species richness, abundance, and community composition. We created metacommunities of varying size using fi ne mesh cages to enclose a gradient from a single bromeliad up to the full forest. We found that species richness, abundance, and biomass increased from enclosed metacommunities to the full forest size and that diversity and evenness also increased in larger enclosures. Community composition was aff ected by metacommunity size across the full gradient, with a more even detritivore community in larger metacommunities, and taxonomic groups such as mosquitoes going locally extinct in smaller metacommunities. We were able to divide the eff ects of metacommunity size into aquatic and terrestrial habitat components and found that the importance of each varied by species; those with simple life cycles were only aff ected by local aquatic habitat whereas insects with complex life cycles were also aff ected by the amount of terrestrial matrix. Th is diff erential survival of obligate and non-obligate dispersers allowed us to partition the beta-diversity between metacommunities among functional groups. Our study is one of the fi rst tests of metacommunity size in a natural metacommunity landscape and shows that both diversity and community composition are signifi cantly aff ected by metacommunity size.

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