Predicting range-shift success potential for tropical marine fishes using external morphology.

With global change accelerating the rate of species' range shifts, predicting which are most likely to establish viable populations in their new habitats is key to understanding how biological systems will respond. Annually, in Australia, tropical fish larvae from the Great Barrier Reef (GBR) are transported south via the East Australian Current (EAC), settling into temperate coastal habitats for the summer period, before experiencing near-100% mortality in winter. However, within 10 years, predicted winter ocean temperatures for the southeast coast of Australia will remain high enough for more of these so-called 'tropical vagrants' to survive over winter. We used a method of morphological niche analysis, previously shown to be an effective predictor of invasion success by fishes, to project which vagrants have the greatest likelihood of undergoing successful range shifts under these new climatic conditions. We find that species from the family of butterflyfishes (Chaetodontidae), and the moorish idol, Zanclus cornutus, are most likely to be able to exploit new niches within the ecosystem once physiological barriers to overwintering by tropical vagrant species are removed. Overall, the position of vagrants within the morphospace was strongly skewed, suggesting that impending competitive pressures may impact disproportionately on particular parts of the native community.