Habitat suitability and niche comparison of sympatric weasels in northwestern Italy

Ecological Niche Models (ENMs) are useful tools for assessing habitat suitability and niche overlap among similar species, but their application to understudied sympatric carnivores remains limited. Three weasel species coexist throughout much of Europe: stoat (Mustela erminea), least weasel (Mustela nivalis), and European polecat (Mustela putorius). Due to their elusive nature, however, little is known about their exact distribution and ecological niches. In this study, we collected occurrences and environmental variables to predict the habitat suitability of these species in northwestern Italy under an ensemble forecasting approach that combined machine learning and maximum entropy algorithms. Moreover, we compared their ecological niches through principal component analysis and Schoener's D overlap metric. A total of 112 occurrences for stoats, 95 for weasels, and 72 for polecats were obtained from a collaborative network and open-source databases. Habitat suitability for the stoat increased with distance from lowland habitats and moderate spring temperatures. For the weasel, suitability increased with distance from agricultural areas and the presence of coniferous forests. Habitat suitability for the polecat was influenced by mild temperatures, rice fields, and slope. Niche overlap analysis revealed a slight similarity between weasels and polecats (Schoener's D = 0.43), while the stoat differed more markedly from the other species. These results suggest that climate change may threaten stoats in the Alps, while land-use change, especially intensive agriculture, likely impacts weasels and polecats. Given current data limitations, our findings also highlight the urgent need for long-term monitoring programs to inform effective conservation strategies for sympatric small mustelids.