Subsidies mediate interactions between communities across space

Most spatial ecologyfocuses on how species dispersal a ects communitydynamics and coexistence. Ecosystems, however, are also commonly connected by ows of resources. We experimentally tested how neighbouring communitiesindirectly in uence each other in absence of dispersal, via resource exchanges. Using two-patch microcosm meta-ecosystems, we manipulated communitycomposition and dynamics, by varying separately species key functional traits ( autotrophversus heterotrophspecies and size of consumer species) and trophic structure of aquatic communities(species growing alone or in presence of competitors or predators). We then analysed the e ects of species functional traits and trophic structure on communitiesconnected through spatial subsidiesin the absence of actual dispersal. Both functional traits and trophic structure strongly a ected dynamics across neighbouring communities. Heterotroph communitiesconnected to autotrophneighbours developed better than with heterotrophneighbours, such that coexistence of competitors was determined by the functional traits of the neighbouring community. Densities in autotroph communitieswere also strikingly higher when receiving subsidiesfrom heterotroph communitiescompared to their own subsidieswhen grown in isolated ecosystems. In contrast, communitiesconnected to predator-dominated ecosystems collapsed, without any direct contact with the predators. Our results demonstrate that because communitycomposition and structure modify the distribution of biomass within a community, they may also a ect communitiesconnected through subsidies throughquantitative and qualitative changes of detritus ows. is stresses that ecosystem managementshould account for such interdependencies mediated by spatial subsidies, given that local communityalterations cascade across space onto other ecosystems even if species dispersal is completely absent.