Abstract:

Recent studies have highlighted both the positive and negative impacts of species invasions. Most of these studies have
been conducted on either immobile invasive plants or sessile fauna found at the base of food webs. Fewer studies have
examined the impacts of vagile invasive consumers on native competitors. This is an issue of some importance given the
controlling influence that consumers have on lower order plants and animals. Here, we present results of laboratory
experiments designed to assess the impacts of unintended aquaculture releases of the Nile tilapia (Oreochromis niloticus), in
estuaries of the Gulf of Mexico, on the functionally similar redspotted sunfish (Lepomis miniatus). Laboratory choice tests
showed that tilapia prefer the same structured habitat that native sunfish prefer. In subsequent interspecific competition
experiments, agonistic tilapia displaced sunfish from their preferred structured habitats. When a piscivore (largemouth bass)
was present in the tank with both species, the survival of sunfish decreased. Based on these findings, if left unchecked, we
predict that the proliferation of tilapia (and perhaps other aggressive aquaculture fishes) will have important detrimental
effects on the structure of native food webs in shallow, structured coastal habitats. While it is likely that the impacts of
higher trophic level invasive competitors will vary among species, these results show that consequences of unintended
releases of invasive higher order consumers can be important.