Environmental niche modeling; present and future potential distribution of garter snakes species from the Trans-Mexican Volcanic Belt

Land-use and climate change are affecting the abundance and distribution of species. The Trans-Mexican Volcanic Belt (TMVB) is a very diverse region due to geological history, geographic position and climate, however, is one of the most disturbed regions in Mexico. Reptiles are particularly sensitive to environmental changes due to their low dispersal capacity and thermal ecology. In this study, we define the environmental niche (a part of it; considering climatic, topographic and land use variables) and potential distribution (present and future) of the five Thamnophis species present in TMVB. To do so, we used the maximum entropy modelling software (MAXENT). First, we modeled to select the most important variables to explain the distribution of each species, then we modeled again only with the most important variables and projected these models to the future (year 2050) considering a middle-moderate climate change scenario (rcp45) and the land use and vegetation variables for year 2050, generated with Land Change Modeler based on the land use change occurred between years 2002 and 2011. We also calculated niche overlap between species in environmental space for the present and the future. Percentage of arid vegetation was a negative important variable for all the species and minimum temperature of the coldest month was selected as an important variable in four of the five species. Distance to Abies forest had a high percentage of contribution for T. scalaris and T. scaliger distribution. We found that all Thamnophis species will experience reductions in their distribution ranges in the TMVB in the future, however, for the whole country, the distribution of T. melanogaster seems to increase in the future. T. scalaris is the species that will suffer the biggest reduction in its distribution; the fact that this species is limited by high temperatures and that cannot shift its distribution upward, as it is already distributed in the highest elevations, can be the cause of this dramatic decline. We found a reduction in niche overlap between species in the future, which means a reduction in the range of suitable combination of variables for the species.