Habitat overlap and body condition in aquatic turtles: are there additive effects between invasive and native species?

Abstract

Trachemys scripta (Reptilia, Emydidae) is among the most widespread invasive reptiles in the world. In general, it is assumed that this species has negative effects on native aquatic turtles based on experiments conducted under controlled conditions. Here, we analysed a 7‒year time series (2013‒2019) of data from captures of three species of turtles (two natives and one alien) from natural populations in the northeastern Iberian Peninsula. We evaluated (i) the interspecific spatial overlap and (ii) the correlation between the scaled mass index (SMI) of the native turtles and the abundance of T. scripta, including an interaction effect between the species. The analyses revealed that T. scripta has relatively low spatial overlap with Emys orbicularis but high overlap with Mauremys leprosa. Overall, the abundance of T. scripta was not associated with significant variations in the SMI of the native species, although for the female E. orbicularis, we detected a negative trend. The analyses also indicated that the abundance of T. scripta does not have an additive effect on the SMI of other turtles, even if there is a negative effect between native species. These findings suggested that the impact of T. scripta on other turtles could be density-dependent.

Habitat occupancy by semi‐aquatic reptiles on an aridity gradient in the western Mediterranean

“…Our findings also showed species‐specific responses to variations in the riparian vegetation. Emys orbicularis is the only species that is associated with wooded riparian communities, possibly because this species can remain active with lower water temperatures than the other species of turtles (9°C vs. 14°C in M. leprosa ; Escoriza et al, 2021). The occurrence of the two most generalist species ( M. leprosa and N. maura ) showed weak or no association with the composition of the riparian vegetation.…”

“…The fieldwork was conducted from 2014 to 2019 by two to three surveyors who characterized 3–6 localities per sampling day (8 hr). The surveys were performed between April and October, coinciding with peak activity periods of the target species (Escoriza, Sunyer, Poch, & Boix, 2021; Schleich et al, 1996). Visual surveys were undertaken along transects using binoculars and rock/log flipping because both techniques have been recommended for studies of the presence of semi‐aquatic reptiles (McDiarmid, Foster, Guyer, Gibbons, & Chernoff, 2012).…”

Home range of three turtle species in Central Yucatan. A comparative study

“…– To estimate spatial overlap between species and season we used the utilization distribution overlap index (UDOI) for each relocation [ 36 ]. This index is recommended for estimating the shared use of space among several species [ 37 , 38 ]. UDOI values range from zero (no overlap) to 1 (uniformly distributed and have 100% overlap) but can be greater than 1 if both UDOI are nonuniformly distributed and have a high degree of overlap [ 36 ].…”

Invasive Amphibians and Reptiles Living in Brazil

“…Several studies have reported impacts of Trachemys scripta elegans in the environments where it has been introduced, among which competition is highlighted as either directly (Polo-Cavia et al, 2010a, 2011; Perez-Santigosa et al, 2013; Kraus, 2015; Pearson et al, 2015; Escoriza et al, 2021) or indirectly negatively influencing the behavior of native freshwater turtles through competition and interference during basking activity (Cadi and Joly, 2004; Polo-Cavia et al, 2010b). Another impact of this invasive turtle is hybridization (Kraus, 2015) with native species of turtles in the Caribbean region (Parham et al, 2013) and in Brazil with the native Brazilian slider ( Trachemys dorbig‑ ni; Figueiredo, 2014).…”