Aquatic communities have been dramatically altered by invasive species with devastating effects on native biodiversity and ecosystem function. Native biodiversity can mitigate the effects of an invader and needs to be considered when predicting the impact of invasive species.  Common carp (Cyprinus carpio) are a ubiquitous, invasive fish that influences fish communities and ecosystem processes.  Predicting the effects of carp is difficult, because most studies have not accounted for diversity differences within invaded systems. Diversity patterns across communities are not random assemblages of species. Yet, designing realistic community patterns for experiments is difficult as local abundance are imperfect predictors of species changes. Nested subset analysis was used to predict nonrandom changes in diversity by quantifying the degree to which species distributions are ordered across a series of systems. Using empirical data, the prevalence of species is arranged based on observations of occurrences in each community producing realistic species combinations.  We examined the effect of carp across a range of fish richness representative of field data in mesocosm tanks with both an additive and substitution design. 

Results/Conclusions:

The fish community patterns from Illinois lakes are strongly nested (measure of disorder 13.34). Thus, the nested subset rank is a realistic order of their removal from the community. Representing the range in prevalence of species found in lakes in decreasing order are bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), golden shiner (Notemigonus crysoleucas), redear sunfish (Lepomis microlophus), red shiner (Cyprinella lutrensis), and fathead minnow (Pimephales promelas).  These results were then used to create the levels of the fish diversity treatments to design mesocosm experiments using two experimental designs.  Carp reduced fish production in both additive and substitution designs.  In the additive design, the magnitude of decrease in fish biomass between carp and no carp treatments decreased with increasing fish richness.  Fish richness was important in explaining native fish production in the substitution design, but was overwhelmed by the carp effects.  The experimental design also influenced the conclusions about the impact of carp on lower trophic levels.  In the additive design, the presence of carp drove the patterns in primary production.  The influence of carp was affected by native fish richness in the substitution design with carp increasing primary production in the lower richness treatments.  Examining the influence of invasive species across a gradient of diversity furthers our understanding of how biodiversity governs ecosystem function by connecting biodiversity ecosystem function theory with invasion ecology.