Can prey-naïveté explain invasive predator success? Anti-predator responses of native Florida fish in the presence of the invasive Hemichromis letourneuxi

Abstract

The African jewelfish (Hemichromis letourneuxi) is a freshwater cichlid that has become highly invasive in Southern and Central Florida over the last 50 years. Jewelfish prey on a multitude of native species, though why jewelfish have become so dominant in invaded waters remains largely unknown. To explain jewelfish success, several scholars have invoked the naïve-prey hypothesis (NPH), which attributes invasive species success to native prey species lacking the anti-predator adaptations needed to survive the new threat. However, these studies failed to manipulate prey-naïveté—a necessary requisite for testing the NPH—and are therefore unconvincing. To address this concern, I captured populations of two indigenous prey species, the eastern mosquitofish (Gambusia holbrooki) and golden topminnow (Fundulus chrysotus), which I then exposed to jewelfish or a native predator, bluegill (Lepomis macrochirus). Within these species, I examined the behavioral differences between populations that had previously coexisted with jewelfish (experienced) versus those that had not (naïve) by filming the interaction between a single native fish and a single predator in aquaria. I examined (1) average speed, (2) vertical distribution, (3) predator-prey distance, and (4) proportion of time behind cover. In the presence of jewelfish, only decreased average speed was observed in experienced compared to naïve native fish, lending support to the NPH. However, that I did not observe significant differences between experienced and naïve individuals in (2)- (4) suggests that other, yet-unknown factors beyond the NPH must also account for jewelfish success. To this end, future studies should be intervention-focused, which would not only address the practical issue of jewelfish eradication but also illuminate the underlying scientific principles behind the establishment of jewelfish in Florida.