Climatic niche shifts from the Last Glacial Maximum to present in North American mammals

Background/Question/Methods

Understanding the dynamics of species’ climatic niches through time is important for understanding how species will respond to ongoing global change. By only examining the current niche of a species and assuming it is static through time, we are underestimating a species potential response to global change. Recent studies have both supported and refuted the stability of climatic niches. Here, I add to this body of work by comparing the climatic niches of 15 mammalian species from the Last Glacial Maximum 21,000 years ago to the present, a time period that encompasses significant climate changes. Climatic niches are constructed using paleoclimate simulations, species occurrences and species distribution modeling. Shifts in niche space are first analyzed using pairwise distances and permutational multivariate analysis of variance and compared to the climate landscape through time to test whether observed shifts are true changes in niche space or whether species are tracking the changing climate. Shifts in niche space are also analyzed using the D-metric and similarity tests to assess niche shifts through time. Finally, the climatic niche space of each species is projected into geographic space in order to determine if shifts in niche space are associated with distributional shifts. 

Results/Conclusions

All species examined except one occupied significantly different climatic niche space from the Last Glacial Maximum to the present according to the permutational multivariate analysis. Shifts in niche space, however, are not greater than the shift in the climatic landscape through time. Therefore, although the climatic niche space of species is shifting, they do not change more than the climate, suggesting the species realized climatic niche is shifting but its fundamental niche is not evolving. The D-metric similarity analyses identified 8 out of 15 species with stable climatic niches and none of the species occupied significantly different climatic niches through time. Because the D-metric analysis takes into account the changing climatic landscape, it also suggests that the species’ fundamental niches are not evolving, although their realized niche may still be shifting. Conservation efforts use species’ realized climatic niches to predict response to ongoing global change. Although species fundamental niches are not evolving through time, their realized niches are shifting, suggesting a significant portion of a species potential response is missing in conservation efforts. To better predict how species will respond to ongoing global changes, inclusion of past climatic realized niche spaces should be included in analyses.