Human influence has created novel ecological communities by introducing nonindigenous species into ecosystems that they may have never encountered previously. As a consequence of potential impacts of non-native species on biodiversity and ecosystem function, it is crucial to recognize what factors contribute to their invasion success. Mechanistic insights from invasion biology indicate that propagule pressure of non-native species, and native community structure, can independently influence establishment success. It is unknown, however, whether regional dispersal dynamics of native species can amplify or reduce these effects on invasion. Recent work from metacommunity ecology demonstrates that native community connectivity can alter community structure relative to isolated communities in a landscape. Native community connectivity may therefore increase biotic resistance to invasion of non-native species, but the relative effects could depend upon the level of propagule pressure. Here, we test the importance of propagule pressure and native community connectivity on invasion success by leveraging native zooplankton communities and the exotic zooplankter Daphnia lumholtzi as a model system. We used a microcosm experiment to evaluate the independent and combined effects of D. lumholtzi propagule pressure (four levels) and native community connectivity (unconnected vs. connected) on invasion success, native species composition, and ecosystem response.
Results/Conclusions
Propagule pressure positively correlated with establishment success and density of the non-native species. Native community connectivity, however, buffered against invasion at low and intermediate levels of propagule pressure but not at high levels. Native species richness was greater in uninvaded than invaded communities regardless of community connectivity. This result was in part driven by a native congeneric competitor that occurred at significantly higher frequencies in uninvaded than invaded communities. There were interactive effects of community connectivity and propagule pressure on ecosystem response through effects on total and inedible phytoplankton biomass. The results indicate that while native community connectivity can reduce the probability of invasion success, high levels of propagule pressure can overcome these effects. Taken together, the results suggest that the relative strength of native community connectivity in the landscape and propagule pressure can interact to determine establishment success of non-native species. Maximizing native community connectivity in a landscape would therefore provide insurance against future invasions.