Climatic niche stability and lability in Holarctic non‐marine ostracods: implications for Quaternary palaeoclimate reconstruction

Quaternary palaeoclimate reconstructions based on fossils of biological proxies such as beetles and ostracods assume that the climatic preferences of living taxa have not changed over time, an ecological uniformitarian approach that should be considered critically. If present ecological lability (niche shifting) of species can be demonstrated, then it almost certainly occurred in the past. Studies of invasive species suggest lability in various organisms including ostracods, not only facilitating invasions but also enabling native taxa to mitigate impacts of interactions with invasive species. Small niche expansions can result in large geographical range shifts. The fundamental ecological niche represents the full range of conditions in which a species can exist, within the boundaries of which its realized ecological niche may change in response to variation in (e.g.) dispersal success or biotic interactions. Bioclimatic niche modelling of three common non‐marine ostracod species with Holarctic distributions demonstrates different Nearctic and Palaearctic climatic niches for two of them, suggesting realized niche shifts; possible niche shifting is also evident in a species believed to have been introduced to Europe and North America from Africa. Despite evidence of lability, the uniformitarian assumption of niche stability can be considered reasonably robust and practical for Holarctic metapopulations of morphospecies, although weaker for regional or local subsets. Holarctic distribution data (combining Nearctic and Palaearctic realized niches) offer the closest approximation to the fundamental niche of a species. Temperature range calibrations of living species for purposes of Quaternary palaeoclimate reconstruction should therefore be based on the widest distribution data available.