A tale of four bears: Environmental signal on the phylogeographical patterns within the extant Ursus species

Aim: Assessing the relevance of niche evolution in the diversification
patterns and geographical distribution of species driven by climate
remains a challenge. We apply an integrative approach to evaluate the role
of the environment on the phylogeography of bear species, incorporating
fossil data to characterize the changes in the ecological niche through
time. We evaluate our approach with the four extant species of bears
within Ursus, the best represented taxon in the fossil record of the
family Ursidae. Location: Eurasia and North America. Taxa: Asian black
bear, Ursus thibetanus; American black bear, U. americanus; Brown bear, U.
arctos; and Polar bear, U. maritimus. Methods: We built a genetic and a
geographical database from all published mitochondrial DNA sequences and
of species occurrence records. We defined the most significant climatic
variables based on each species ecological realm using correlation
matrices, and characterized the ecological niches and existing
environmental conditions with ellipsoid models. We inferred their current
and Last Glacial Maximum (LGM) ecological niche modellings (ENMs) and
compared the results with the fossil record. We estimated the times of
divergence (d‐loop sequences) of lineages and applied a phyloclimatespace
approach to discern the phylogeographical patterns along each species’
ecological space. Results: Ecological niche modelling showed wider niches
for U. thibetanus and U. americanus encompassing higher temperature and
precipitation, while U. arctos and U. maritimus showed an opposite
pattern. LGM models were consistent with the fossil record, predicting
55%–89% of the fossil occurrences (within their suitability areas). The
phyloclimatespace revealed different degrees of environmental signal in
the lineages’ phylogeographical patterns and ecological trajectories
associated with LGM climatic conditions. Results indicated habitat
tracking and ecological expansion since the LGM towards more extreme
precipitation and temperature conditions for three species, except U.
maritimus that showed ecological niche reduction. Main Conclusions:
Incorporating fossil information from the LGM improved our
characterization and interpretation of ecological models, by enabling
definition of the limits of the climatic conditions explored by the
species in the past. Our approach also provided insights about the
existing set of environmental conditions shaping the ecological niche
divergence of Ursus bears. We were able to depict key features of the
lineages’ evolutionary history, ecology and distribution, revealing the
dynamics of niche occupation and the environmental signal on the
phylogeographical patterns of Ursus.