Looking through the predator's eyes: another perspective in naïveté theory.
The topic of biological invasion has adopted the concepts of neophobia and dietary conservatism to explain why some species are reluctant to include nonnative species in their diets, with prey naïveté predicting that prey would not be able to recognize novel predators in the environment. This is particularly true for fish, for which studies are rare, mainly in natural environments. Here, the existence of feeding selectivity in terms of prey origin was investigated in nature by quantifying the contribution of nonnative prey to the diets of native and nonnative predators. Three distinct rivers in the upper Paraná River basin (Brazil) and 13 piscivores were used to test the hypothesis. Out of the 650 possible trait combinations, only prey body shape (sagittiform) and predator relative body height were found to be correlated. Even though native and nonnative prey presented similar functional traits, very strong selectivity by prey origin was observed, with native predators positively selecting native prey. Native predators possibly do not recognize nonnative prey or lack the necessary ability to prey upon nonnative prey. Such findings show that, for several predators, prey origin does matter. There are many implications of "predator naïveté", as an increasing number of nonnative species are being introduced worldwide, with advances in such area enabling a better understanding of several limitations in biological invasions. Perhaps looking through the predator's eyes might bring some novel perspective and help to understand some as yet unexplainable paradigms in biological invasions.