Population density contributes to the higher functional response of an invasive fish

Abstract

Invasive species often have higher functional responses than native analogs. A better understanding of the functional response of invasive species could help explain the effect of these species on native prey communities, and aid in the development of tools for predicting invasion impact. We investigated the role of population density and location along the invasion pathway in determining the functional response of an invasive fish. We used invasive round goby (Neogobius melanostomus) collected from the Trent-Severn Waterway in Ontario, Canada to test for differences in the functional response of fish from high and low density sites, and from different locations along the invasion pathway. We also compared the functional response of round goby with that of northern logperch (Percina caprodes), a native species occupying the same niche. The density of the invasive predator population influenced its functional response, with attack rate being significantly higher for fish from high-density sites compared to fish from low-density sites. Functional response of individuals living at the invasion front was not significantly different from those living in established areas. The higher functional response of round goby compared to its native analog was associated with shorter handling time. Patterns in functional response curves were not explained by differences in diet among wild populations. Our research demonstrates that population density influences the functional response of an invasive species, and therefore should be accounted for when evaluating the functional response of a potential invader.