Influence of invader-driven heterogeneity on metacommunity dynamics

Background/Question/Methods

Introducing heterogeneity into a metacommunity can have diverse effects on local and regional biodiversity. While a large body of research has focused on abiotic heterogeneity within metacommunities, much less research has focused on how biologically-induced heterogeneity influences metacommunity dynamics. Invasive ecosystem engineers alter ecosystems in novel ways such that they can have not only strong local, but also regional effects if they are part of a larger metacommunity where invaded and non-invaded habitats are connected by dispersal.  As invasion intensity increases and more of the individual sites within a metacommunity are invaded, there is an increase in biological heterogeneity that can alter local and regional biodiversity. We conducted a mesocosm study using the invasive zebra mussel (Dreissena polymorpha) to create a biologically-induced heterogeneity gradient across four metacommunity treatments to determine how invasion intensity within a metacommunity influences local and regional zooplankton biodiversity. We created a gradient of invasion intensity in replicated metacommunities that consisted of three communities connected by dispersal. Heterogeneity was introduced by inoculating 0, 1, 2, or 3 communities within each metacommunity with zebra mussels. We then measured local and regional zooplankton biodiversity over a period of six weeks. 

Results/Conclusions

Zebra mussels significantly reduced local biodiversity in invaded communities. However, the extent to which local biodiversity was reduced was determined by the number of invaded communities within the metacommunity: Local biodiversity of invaded communities was highest in the metacommunity with two-invaded communities and lowest in the fully-invaded metacommunity. Conversely, the local biodiversity of communities that were not invaded by zebra mussels was unaffected by the number of invaded communities within the metacommunity, suggesting that invasion intensity within the metacommunity does not influence local biodiversity of non-invaded communities. Regional biodiversity was significantly lower in the fully invaded metacommunity, but did not differ between the non-invaded metacommunity and the two intermediately invaded metacommunities. These results suggest that intermediate levels of biologically-induced heterogeneity can have diverse effects on local biodiversity but may not be as influential on regional biodiversity.