Predator recognition of native but not invasive turtle predators by naïve anuran tadpoles

Abstract

The impact of alien predators on prey populations is well known by conservation biologists, but little attention has been paid to the negative effects that the introduction of exotic predators may have on native predators through competition for food. In the Iberian Peninsula, the red-eared slider, Trachemys scripta elegans, and other exotic freshwater turtles have been introduced, competing and displacing the native endangered terrapins (the European pond turtle, Emys orbicularis, and the Spanish terrapin, Mauremys leprosa). Although the nature of competitive interactions remains unclear, direct competition for food is likely to occur. Both native and invasive freshwater turtles are common predators of amphibian tadpoles. Naive amphibian tadpoles are known to recognize and respond to local predators with no prior experience, but tadpoles might not recognize new predatory species, since they have not shared a long evolutionary history with them. We examined the ability of four species of Iberian anuran tadpoles to recognize and respond to chemical cues from invasive and native freshwater predatory turtles. Three of the four tadpole species tested reduced their swimming activity when cues from native turtles were present in water, but not when cues belonged to exotic turtles. This inability of tadpole prey to respond innately to chemicals from introduced predatory turtles might be one of the causes that explains the displacement of native populations of Iberian terrapins by invasive exotic turtles, and may help clarify why alien predators sometimes prosper better in new habitats than locally adapted predators.