LAUSR

Invasive predators might serve as ecological filters for prey communities, either through non-consumptive or consumptive effects. The Western Mosquitofish (Gambusia affinis [Baird and Girard, 1853]) is an invasive non-native fish that affects native aquatic communities, potentially because of effects on oviposition or initial colonization of habitats (non-consumptive effects), post-colonization effects (i.e., consumptive effects), or a combination of both non-consumptive and consumptive effects. We conducted a mesocosm experiment to examine non-consumptive and consumptive effects of G. affinis on colonization of experimental ponds by native macroinvertebrates. We predicted that, if G. affinis affects macroinvertebrates through non-consumptive effects, there would be lower abundances in both the non-lethal (caged G. affinis) and lethal (free-ranging G. affinis) treatments compared to the control (no G. affinis), whereas, if the effect of G. affinis is primarily due to consumptive effects, there would be lower abundances of macroinvertebrates in the lethal treatment compared to the non-lethal and control treatments. Most macroinvertebrate taxa (dytiscid beetles, baetid Ephemeroptera, corixid and gerrid hemipterans, libellulid odonates) were less abundant, or even absent, in the presence of G. affinis in the lethal treatment compared to their abundance in the non-lethal G. affinis treatment; however, notonectids were not affected by treatment. The invasive fish predator, G. affinis, therefore, can act as an ecological filter for macroinvertebrates in invaded aquatic habitats, primarily through lethal consumptive effects.