Aim: Species living on steep environmental gradients are expected to be especially sensitive to global climate change. Here, we combined genetic, ecological niche modelling and climatic niche comparisons to investigate the influence of climate on the biogeography of three alpine species with overlapping ranges.

Location: Te Waipounamu (South Island) Aotearoa–New Zealand.

Taxon: Endemic alpine-adapted Cataontopinae grasshoppers.

Methods: We used niche modelling to estimate and project the potential niche of three focal species under past and future climate scenarios. Vulnerability assessments were performed using niche factor analyses. Demographic trends and phylogeographic structure were investigated using samples from 15 mountain tops to generate mitochondrial DNA haplotype networks and population genetic statistics.

Results: Niche models and genetic data suggest suitable habitat for all three alpine species was more widespread and contiguous in the past than today. Demographic analyses indicate in situ survival rather than post-Pleistocene colonisation of current habitat. Population structuring and genetic divergence suggest that mountain uplift during the Pliocene and environmental barriers during Pleistocene glacial and interglacial stages shaped contemporary population structure of each species. Though geographically overlapping, niche analyses suggest these alpine species are not ecologically identical, and each shows similar but distinct responses to environmental change, but all will lose intraspecific diversity through population extinction.

Main conclusions: Climatic, biological and geophysical factors controlled population structuring of three cold-adapted species during the Pleistocene with a legacy of spatially separate intraspecific lineages. Ecological niche models for each species emphasise distinct combinations of environmental proxies, but all are expected to experience severe habitat reduction during climate warming. Increased global temperatures drive available habitat to higher elevation resulting in population contractions, range shifts, habitat fragmentation, local extinctions, and genetic impoverishment. Despite alpine species not being ecologically identical, we predict all mountain biota will lose significant genetic diversity due to global warming.