Propagule pressure and native community connectivity interact to influence invasion success in metacommunities
10 June 2019King, Gabrielle; Howeth, Jennifer
Mechanistic insights from invasion biology indicate that propagule pressure of exotic species and native community structure can independently influence establishment success. The role of native community connectivity via species dispersal and its potential interaction with propagule pressure on invasion success in metacommunities, however, remains unknown. Native community connectivity may increase biotic resistance to invasion by enhancing species richness and evenness, but the effects could depend upon the level of propagule pressure. In this study, a mesocosm experiment was used to evaluate the independent and combined effects of exotic propagule pressure and native community connectivity on invasion success. The effects of three levels of exotic Daphnia lumholtzi propagule pressure on establishment success, community structure, and ecosystem attributes were evaluated in native zooplankton communities connected by species dispersal versus unconnected communities, and relative to a control without native species. Establishment of the exotic species exhibited a propagule dose-dependent relationship with high levels of propagule pressure resulting in the greatest establishment success. Native community connectivity, however, effectively reduced establishment at the low level of propagule pressure and further augmented native species richness across propagule pressure treatments. Propagule pressure largely determined the negative impacts of the exotic species on native species richness, native biomass, and edible producer biomass. The results highlight that native community connectivity can reduce invasion success at a low propagule dose and decrease extinction risk of native competitors, but high propagule pressure can overcome connectivity-mediated biotic resistance to influence establishment and impact of the exotic species. Together, the results emphasize the importance of the interaction of propagule pressure and community connectivity as a regulator of invasion success, and argue for the maintenance of metacommunity connectivity to confer invasion resistance.