Ecological distribution of Stephanodiscus niagarae Ehrenberg in central Mexico and niche modeling for its last glacial maximum habitat suitability in the Nearctic realm

Stephanodiscus niagarae Ehrenberg is currently restricted to specific regions of central Mexico, however, during the late Pleistocene, it had a wider distribution in the country. This change in distribution is similar to those observed for several organisms that migrated southwards during cold, glacial climates, supporting the hypothesis that central Mexico acted as glacial refugia for these species. This study aims to support this hypothesis for S. niagarae as well as to analyze its ecological distribution in modern environments in central Mexico. For this purpose we studied 18 samples from 16 lakes located around Mexico City, selected among 46 lakes along the Trans-Mexican Volcanic Belt. Diatom assemblages in superficial sediments, and climatic, hydrochemistry, and nutrient parameters of each lake were analyzed by means of canonical correspondence analyses. Additionally, we created an ecological niche model (ENM) with modern occurrence data (n = 47) and environmental variables (WorldClim) to produce potential distribution maps of S. niagarae during the present time and under the LGM conditions in the Nearctic realm. S. niagarae was recorded only in 4 sites in central Mexico (abundances < 10%) associated with temperate, subhumid conditions in freshwater lakes with [Mg2+] − [Ca2+] − [HCO3−] ionic dominance and high turbidity, mesotrophic to hypertrophic systems (based on chlorophyll a values), but with a tendency to P-limitation. In our study sites S. niagarae showed low abundances in diatom assemblages dominated by Aulacoseira spp. Temperature (annual mean, coldest and warmest quarters means) was identified by ENM as the main environmental variable controlling its distribution, with its highest modern support in the USA, southern Canada, and a restricted distribution in the highlands of western and central Mexico. Whereas, the LGM scenario (− 5.5 °C) identified the western and central highlands in Mexico and southern USA as the highest probability distribution areas supporting the approach that the Sierra Madre Occidental could have acted as a migration corridor offering suitable habitats for a southward migration into central Mexico during colder (glacial) periods. In conclusion, S. niagarae distribution in the central and western mountains of Mexico is controlled by temperature changes and its presence may be associated with colder (glacial) periods.