When the Invader Becomes the Invaded: Temporal Variation of Gambusia affinis and Centrarchid Sunfish in Two Small Ponds

Piscivory, intraguild predation, and competition by native fish can limit the ability of non-native fish to invade or persist in invaded aquatic ecosystems. Gambusia affinis (Western Mosquitofish) is one of the most invasive species of freshwater fishes; however, the presence of native piscivorous or facultatively piscivorous fish might negatively affect their populations. We examined the effect of an “invasion” of native Lepomis megalotis (Longear Sunfish) on a non-native population of Western Mosquitofish in a small pond in central Ohio (Olde Minnow Pond). We also monitored fish populations in a nearby pond (Wood Duck Pond) that had small populations of non-native Western Mosquitofish and native Lepomis macrochirus (Bluegill Sunfish) throughout the study period. The abundance of Western Mosquitofish in minnow traps in Olde Minnow Pond was greatly reduced after the “invasion” of Longear Sunfish. In contrast, Wood Duck Pond showed no decline in Western Mosquitofish numbers in traps over the same period. In addition, the proportion of male Western Mosquitofish in Olde Minnow Pond was greater after the “invasion” of Longear Sunfish, but no such change was observed in Wood Duck Pond. In general, male and female body size did not differ between the pre- and post-invasion periods. Our results suggest that the invasion, abundance, and persistence of populations of non-native Western Mosquitofish can be limited by the presence of native Lepomis.