Habitat loss is one of the major threats to global biodiversity. As local communities may differ considerably in their contributions to the biodiversity and ecosystem functioning of metacommunities, it has been suggested that conservation priority should be given to functionally disproportionately important communities (i.e., keystone communities). However, we know little about what characteristics a local community has that make it a keystone community. We conducted a laboratory protist microcosm experiment to identify keystone communities and to examine the consequences of losing these keystone communities for biodiversity and ecosystem functioning. Each of our metacommunities contained three local communities that were lined up with one middle community connected to the other local communities. We incubated the three local communities under the light or dark conditions to manipulate environmental heterogeneity. We used eight protist species, including heterotrophic ciliated protozoans and autotrophic microalgae. The loss of one of the local communities would result in the reduction in environmental heterogeneity and/or patch connectivity of the metacommunities. We monitored the alpha-, beta-, and gamma- diversity, and a series of ecosystem functions for each metacommunity for eight weeks.
Results/Conclusions
Our results showed that the removal of the middle communities of a metacommunity, which resulted in a decrease in habitat connectivity in the metacommunity, reduced alpha- and gamma-diversity and increased beta-diversity. The removal of local communities with unique environmental conditions, which resulted in a decrease in habitat heterogeneity, reduced alpha- and gamma-diversity, but increased beta-diversity. Moreover, when removing local communities contributing to both connectivity and heterogeneity of metacommunities, we observed a drastic decline in their alpha- and gamma-diversity, as well as a decline in protist community biovolume production and organic matter decomposition. The removal of these local communities resulted in greater community- and ecosystem-level impacts than the removal of other communities, qualifying them as keystone communities. Our study highlights the important role of keystone communities in maintaining biodiversity and ecosystem functioning of metacommunities.