Drivers of change in the realised climatic niche of terrestrial mammals

The breadth of a species’ climatic niche is an important ecological trait
that allows adaptation to climate change, but human activities often
reduce realised niche breadth by impacting species distributions. Some
life-history traits, such as dispersal ability and reproductive speed,
allow species to cope with both human impact and climate change. But how
do these traits interact with human pressure to determine niche change?
Here we investigate the patterns and drivers of change in the realised
climatic niche of 258 terrestrial mammal species. Our goal is to
disentangle the impacts of human land use, climate change, and life
history. We quantified 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 difference 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 one in six retained a
stable niche. Climate change and distribution change were the strongest
correlates of species niche change, followed by biogeography,
anthropogenic land use, and life-history traits. Factors that increased
the probability of niche shrink included: overall climatic instability,
reduction in distribution range, historical land use, large body mass, and
long weaning age. Species with these characteristics might require
interventions that facilitate natural dispersal or assisted colonisation
to survive rapidly changing climates.