Competition for basking places between the endangered European pond turtle (Emys orbicularis galloitalica) and the introduced red-eared slider (Trachemys scripta elegans)

Large numbers of red-eared sliders (Trachemys scripta elegans) have been imported into Europe for several years as part of the pet trade. These alien turtles have entered habitats where they interact with native pond turtles (Emys orbicularis). We investigated competition for basking sites, because optimal basking sites may be a restricted resource in the wild. We used experimental ponds to compare basking-place selection between single-species groups and mixed-species groups. Both species preferred basking places in open deep water. In mixed groups the sliders outcompeted the European turtles for preferred basking places. Although competition for basking places is only one component of resource partitioning between these two species, it provided an insight into the relationships between an introduced and a native species. Behavioural asymmetries like those detected in our experiments argue for the caution principle in the animal trade.