Intraguild predation may facilitate coexistence of native and non-native fish.
Although largely ignored, coexistence of native species with non-native species is the rule rather than the exception in the contemporary world. Therefore, understanding the mechanisms that facilitate coexistence of native species with non-native invasive species is critical in implementing effective management strategies to conserve native biodiversity. We conducted field mesocosm experiments to study reciprocal predation between an invasive fish species (Western mosquitofish Gambusia affinis) and an endangered fish species (Mohave tui chub Siphateles bicolor mohavensis). Additional predation vulnerability modelling was conducted to assess the vulnerability of a given prey population to predation by a gape-size limited predator population. Adult mosquitofish reduced Mohave tui chub recruitment through predation on tui chub larvae. Reciprocally, adult tui chubs limited the population growth of mosquitofish through predation on adult mosquitofish, providing evidence for intraguild predation (IGP). Mohave tui chub predation on adult mosquitofish was apparently gape-size limited and larger female mosquitofish avoided tui chub predation. Vulnerability modelling provided additional information on gape-size limited reciprocal predation between these two fish species and insights on the effects of such IGP on persistence of Mohave tui chub in the presence of invasive mosquitofish. Synthesis and applications. Our results collectively show size-structured intraguild predation (IGP) between a native endangered fish and an invasive fish species, which may facilitate coexistence of these species. Invasive species often prey on native species, thus IGP may be a common but neglected phenomenon for invaded systems. Therefore, understanding the complex interactions among native and non-native species in the whole-ecosystem context may help conservation practitioners identify novel management strategies. This may be especially necessary when natural, uninvaded habitats for native species become increasingly scarce due to alterations resulting from multiple forms of human impact.