On the environmental background of aquatic organisms for ecological niche modeling: a call for caution

Ecological niche modeling (ENM) is a technique widely used in many disciplines of science. Recently, the extent of using the environmental background for ENM calibration has been pointed out as playing a crucial role in determining model outcomes. However, when modeling freshwater species, the need for a background refinement has been ignored and its consideration possesses important implications not taken into account before. Here, using Maxent algorithm and global occurrence data characterizing the distribution of the invasive freshwater turtle, Trachemys scripta, we performed ENM transfer and compared native and invasive niche estimates for the species in the environmental space. We used two environmental backgrounds: (a) a traditional area, based on the current distribution and dispersal capacity of the species, and (b) a more restricted area, which corresponds exclusively to freshwater bodies. Our analysis revealed strong differences between the traditional and the restricted backgrounds in niche transferability, with differences in Maxent probability values ranging from − 0.59 to 0.41. Also, during comparisons between native and invasive niches, the niches were more similar when the traditional approach was used, compared to the restricted approach. Our results highlight the importance of considering the biological restriction of the species when establishing the extent of the background in ecological niche modeling; in this case, a more restricted area represented by freshwater environments.