Dispersal and climate warming determine range shift in model reptile populations

Average air temperature is predicted to rise by at least 3 °C across the 21st century. As individual sex (male or female) is determined by temperature in many reptiles, there are concerns that climate warming will skew offspring sex ratios and local species extinctions will follow. Range shift away from hotter areas through dispersal may prevent species extinctions in many reptiles with temperature-dependent sex determination (TSD), and could be facilitated or impeded by sex-biased populations at the expanding edge. We used a simulation model to examine the role of sex-determining mechanism [TSD and genotypic sex determination (GSD)], climate warming and dispersal in determining range shift and population growth in reptiles. Dispersal influenced range shift (after climate warming) in TSD species to a greater extent than in GSD species. Our novel finding is that biased sex ratios may influence range shift, through the mixing of the rare sex (females) with males located at the colder range edges, as both sexes disperse. However, if faced with climate warming of 3 °C over the next 100 years many TSD reptiles will show limited capacity for range shift.