Alien Invasive Slider Turtle in Unpredicted Habitat: A Matter of Niche Shift or of Predictors Studied? Dennis Ro ¨ dder 1 , Sebastian Schmidtlein 2 , Michael Veith 1 , Stefan Lo ¨ tters 1 * 1 Biogeography Department, Trier University, Trier, Germany, 2 Sebastian Schmidtlein, Department of Geography, Bonn University, Bonn, Germany Abstract Background: Species Distribution Models (SDMs) aim on the characterization of a species’ ecological niche and project it into geographic space. The result is a map of the species’ potential distribution, which is, for instance, helpful to predict the capability of alien invasive species. With regard to alien invasive species, recently several authors observed a mismatch between potential distributions of native and invasive ranges derived from SDMs and, as an explanation, ecological niche shift during biological invasion has been suggested. We studied the physiologically well known Slider turtle from North America which today is widely distributed over the globe and address the issue of ecological niche shift versus choice of ecological predictors used for model building, i.e., by deriving SDMs using multiple sets of climatic predictor. Principal Findings: In one SDM, predictors were used aiming to mirror the physiological limits of the Slider turtle. It was compared to numerous other models based on various sets of ecological predictors or predictors aiming at comprehensiveness. The SDM focusing on the study species’ physiological limits depicts the target species’ worldwide potential distribution better than any of the other approaches. Conclusion: These results suggest that a natural history-driven understanding is crucial in developing statistical models of ecological niches (as SDMs) while ‘‘comprehensive’’ or ‘‘standard’’ sets of ecological predictors may be of limited use. Citation: Ro ¨ dder D, Schmidtlein S, Veith M, Lo ¨ tters S (2009) Alien Invasive Slider Turtle in Unpredicted Habitat: A Matter of Niche Shift or of Predictors Studied? PLoS ONE 4(11): e7843. doi:10.1371/journal.pone.0007843 Editor: Ross Thompson, Monash University, Australia Received July 21, 2009; Accepted October 7, 2009; Published November 24, 2009 Copyright: ß 2009 Ro ¨ dder et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work has been supported by grants from the ‘Graduiertenforderung des Landes Nordrhein-Westfalen’ and the Ministry of Education, Science, Youth and Culture of the Rhineland-Palatinate state of Germany (‘Die Folgen des Global Change fur Bioressourcen, Gesetzgebung und Standardsetzung’). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: loetters@uni-trier.de Introduction Alien invasive species are a concern in nature conservation as they may have a negative impact on native biodiversity [1]. To learn about the capability or risk of alien invasive plants and animals, Species Distribution Models (SDMs) are a powerful tool. A SDM characterizes the ecological niche of a species, based on ecological predictors recorded at the known distribution, and projects it into geographic space uncovering its potential distribution [2–5]. In recent times, there have been numerous examples in which SDMs were applied to identify areas which are suitable to certain alien invasive species. These generally aimed on climatic suitability, i.e. the species’ climate envelopes [6–10]. In these studies, the climate envelope was understood as a part of a species’ fundamental niche, which is the entirety of abiotic and biotic conditions under which it can persist [5,11]. The portion of the fundamental niche exploited by a species is commonly limited by interactions with other species (e.g. competition, predation) as well as by spatial accessibility (e.g. through presence/absence of physical barriers) (Figure 1A) [12,13]. It is known that fundamental niches are subject to evolution. In a recent review, it has been shown that, independent of the taxonomic group, the fundamental niche can remain stable for tens of thousands of years or that it can substantially shift within only a few generations [14]. However, there is still a considerable lack of knowledge regarding the processes triggering niche shifts. It has been pointed out that the establishment and geographic range extension alien invasive species can provide valuable insights into ecological and evolutionary processes [15]. Indeed, some recent studies have addressed the question of rapid ecological niche shifts during invasion processes. Using SDMs, it was found that in the Spotted knapweed (Centaurea maculosa) the climate envelopes in its native range (western North America) differed from its invasive range in Europe [16]. Similarly, it was demonstrated in a SDM approach that Fire ants (Solenopis invicta) can be ascribed to climate envelopes in their invaded range (North America) from which they are absent in their native South American range [17]. These observations could represent a shift either in the fundamental (Figure 1B) or realized niches (Figure 1C). Since alien invasive species, by definition, access areas they were absent from before, the ‘new’ climate envelope might most likely simply represent a better exploitation of the existing fundamental niche (Figure 1C). To the best of our knowledge, information on the physiological limits of Centaurea maculosa and Solenopis invicta is sparse. Hence, it cannot be ruled out that the climate predictors chosen in previous approaches mentioned [16,17] are not physiologically limiting for the native range borders of these species. The striking question arising is genetic novelty (niche evolution) versus a better insight into the existing fundamental niche breadth. We claim that this should be more properly PLoS ONE | www.plosone.org 1 November 2009 | Volume 4 | Issue 11 | e7843