Interactions Between Non-Native Western Mosquitofish and Native Bluegill Sunfish: Mesocosm Experiments.

Aquatic ecosystems are often negatively affected by invasive species. However, biotic resistance by native species, either by competition or predation, can reduce the impacts of invasions by non-native species. The Western Mosquitofish () is one of the most impactful invasive species of freshwater fish and cause declines in native fish populations. Using two mesocosm experiments conducted in different years, we examined the ecological interactions between juveniles of the native fish, Bluegill Sunfish (), and adults of the invasive fish, . We found evidence for interactions between and . However, interactions did not appear symmetric, with generally more affected by intraspecific interactions than interspecific interactions whereas was more affected by interspecific interactions than intraspecific interactions. The presence of either species of fish led to a decrease in the number of large zooplankton and a tendency for a decrease in the total number of zooplankton. Based on these results, native appear to be able to reduce the ability of non-native to establish or maintain populations through both competition and predation (i.e., acting as an intraguild predator). The consistency of our results across both experiments, with their different designs and their occurring in different years, gives weight to these conclusions. The reduction of or prevention of establishment of populations of invasive would likely benefit the aquatic communities of ponds with fish, especially small-bodied native fish.