No 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.

The red-eared slider (Trachemys scripta elegans) is a worldwide highly invasive species, currently introduced in most freshwater habitats as a consequence of massive pet trade. In the Iberian Peninsula, this species is competing with and displacing the endangered native Spanish terrapin (Mauremys leprosa). Sliders are considered environmentallyaggressive turtles, capable of threatening or biting other individuals during competitive activities such as feeding. We hypothesized that agonistic behavior of introduced sliders against native terrapins might negatively affect the feeding efficiency of M. leprosa. We compared food ingestion of turtles and aggressive interactions during feeding, under situations of conspecific and heterospecific competition. The amount of food ingested by native and introduced turtles was similar under conspecific competition, but T. scripta ingested a greater percentage of food supplied under heterospecific competition. Also, introduced sliders initiated most of the aggressions observed during feeding activity, and aggression was more frequently directed to heterospecifics. Our results suggest a more aggressive and competitive behavior of introduced T. scripta in vying for food resources, which might contribute to explain the observed displacement of native populations of M. leprosa.

The red-eared slider (Trachemys scripta elegans) is currently introduced in many Mediterranean countries, where it behaves as an invasive species that competes and displaces native populations of the endangered Spanish terrapin (Mauremys leprosa). However, the nature of competitive interactions is relatively unknown. During basking activity, factors like greater body size or pre-existing behavioral adaptations to an original habitat with higher levels of interspecific competition might confer competitive advantages to introduced T. scripta with respect to native terrapins. We hypothesized that competition for basking places with the introduced T. scripta might negatively affect the efficiency of basking and thermoregulation of the native Spanish terrapin. We experimentally analyzed the basking activity of T. scripta and M. leprosa under occasional and long-term situations of intra-and inter-specific competition. Native M. leprosa subjected to interspecific competition reduced their basking activity, basked for shorter periods than T. scripta, and avoided basking stacked with the exotic turtles. These results suggested the displacement from the basking sites of the native terrapin by the introduced T. scripta. The decreased basking activity of native M. leprosa when competing directly for basking places with introduced sliders may lead native terrapins to a loss in the efficiency of physiological functions related to ineffective thermoregulation, such as digestion or locomotor performance, thus favoring the expansion of the invasive species.