Drivers of change in the realised climatic niche of terrestrial mammal species

Abstract

The breadth of a species climatic niche is an important ecological trait that allows adaptation to climate change, but human activities drive niche erosion. Life-history traits, such as dispersal ability and reproductive speed, instead allow species to cope with climate change. But how do these characteristics act in combination with human pressure to determine niche change? Here we investigate the patterns and drivers of change in the realised climatic niche of 589 terrestrial mammal species. Our goal is to disentangle the impacts of humans, climate change, and life history. We calibrated the past and present climatic niches of each species by considering past climatic conditions (Mid Holocene) within their pre-human impact distributions, and current climatic conditions within the current distributions. Depending on the relationship between past and current niche, we defined four categories of change: "shrink", "shift", "stable", and "expand". We found over half of the species in our sample have undergone niche shrink, while only 15-18% of species retained a stable niche. After controlling for biogeography, climatic factors were the strongest correlates of species niche change, followed by anthropogenic pressure and species life history. Factors that increased the probability of niche shrink include: overall climatic instability in the area (both intermediate or high), large body mass, long gestation time, highly carnivorous or herbivorous diets, historical land-use change, and current human population density. We identified the conditions under which species are less likely to maintain their niche breadth, potentially losing adaptation capacity under climate change. Species with these characteristics require interventions that facilitate natural dispersal or assisted colonisation, to survive to rapidly changing climates.