Interspecific Differences in Responses to Predation Risk May Confer Competitive Advantages to Invasive Freshwater Turtle Species

Abstract

The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red‐eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments.

Interference competition between native Iberian turtles and the exotic Trachemys scripta

“…In contrast, M. leprosa hidden within the shell are more prone than T. scripta to overheating or predation due to their more flattened shape. Thus, as expected, M. leprosa escapes quickly to the water when facing a terrestrial threat while T. scripta tends to remain for longer in land, hidden inside the shell (POLO-CAVIA et al, 2008). These inter-specific differences in response to predation risk between native and introduced turtles may result advantageous for the introduced species in altered habitats where human pressure has considerably reduced the risk of predation by natural predator species.…”

“…In these habitats, where terrestrial predators are reduced and human pre-sence carries little risk of actual predation, T. scripta could avoid unnecessary flees to water and subsequently basking interruptions by remaining hidden in the shell (POLO-CAVIA et al, 2008). These findings emphasise the importance of further studies linking habitat conservation with invasion success.…”

“…overheating risk, interruption of basking, loss of foraging or mating opportunities, etc.) (SIH et al, 1998;MARTÍN et al, 2005;POLO-CAVIA et al, 2008). In these cases, the high thermal inertia of T. scripta protects turtles from desiccation (CARR, 1952;WYNEKEN et al, 2008;POLO-CAVIA et al, 2009b) and its spherical shell shape reduces the risk of successful predatory attacks, as it hampers the capture by snapping jaws or avian predators (PRITCHARD, 1979;JANZEN et al, 2000).…”

“…Hence, the inability of amphibian tadpoles to innately recognise chemical cues from exotic predatory turtles may represent a further competitive advantage for introduced turtles over native ones in the Iberian Peninsula (POLO-CAVIA et al, 2010b). However, the magnitude and impact of this evolutionary release on native populations of Iberian turtles remains uncertain, as amphibian prey might acquire learned recognition of novel competitive predators and enhance survival (MIRZA & CHIVERS, 2000;GAZDEWICH & CHIVERS, 2002;POLO-CAVIA & GOMEZ-MESTRE, 2014).…”

Establishment risk from pet-trade freshwater turtles in the European Union

“…When it reaches adulthood, however, it loses its attractive coloration, and hobby keepers often release their turtles into local waters (Cadi and Joly, 2003). At these locations, the released individuals may indirectly exclude or outcompete native turtle species (Cadi and Joly, 2003;Polo-Cavia et al, 2008) and can indeed negatively affect other species in aquatic communities (Mlíkovský and Stýblo, 2006;Teillac-Deschamps and Prevot-Julliard, 2006;Pešát, 2008 , and Italy (Sindaco et al, 2006). Although it seems reasonable to stop import of the pond slider, this does open up the possibility for introduction of other invasive species, inasmuch as the demand for aquatic turtles by hobby keepers still persists.…”