Darwin’s famous naturalization hypothesis states that the probability of an invasive species successfully introducing itself to a new environment decreases due to competition if closely related species are already present. Though this has proven true for many invasives, the opposite appears true for frogs. Researchers at the University of Sydeny, Australia, recently published a study examining a suite of successful and unsuccessful amphibian invasions across 162 species. It turns out that chance of a successful invasion increases significantly as the number of related species increases. Invader success is also higher on islands than mainlands, and higher in areas with abiotic conditions similar to the invader’s natural habitat.
Why would invaders be more likely to succeed if closely related species, who undoubtedly use similar resources and occupy similar habitats, are present? The “preadaptation hypothesis” suggests that the very attributes of an ecosystem that allow an invader’s relatives to thrive allow the invader to establish itself as well- that is to say, the resource competition between relatives is not as important as the suitability of the habitat for both species. (Could humans learn a thing or two from frogs?) Preadaptation is known to be true for some invasive plants, but these findings represent the first example of support for the preadaptation hypothesis in an animal. For conservationists interested in endangered frogs, this information will no doubt be valuable in searching for suitable new habitats.
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