Global mountain topography and the fate of montane species under climate change

Increasing evidence indicates that species throughout the world are responding to climate change by shifting their geographic distributions(1-3). Although shifts can be directionally heterogeneous(4,5), they often follow warming temperatures polewards and upslope(1,2,6). Montane species are of particular concern in this regard, as they are expected to face reduced available area of occupancy and increased risk of extinction with upslope movements(6-9). However, this expectation hinges on the assumption that surface area decreases monotonically as species move up mountainsides. We analysed the elevational availability of surface area for a global data set containing 182 of the world's mountain ranges. Sixty-eight per cent of these mountain ranges had topographies in which area did not decrease monotonically with elevation. Rather, mountain range topographies exhibited four distinct area-elevation patterns: decreasing (32% of ranges), increasing (6%), a mid-elevation peak in area (39%), and a mid-elevation trough in area (23%). These findings suggest that many species, particularly those of foothills and lower montane zones, may encounter increases in available area as a result of shifting upslope. A deeper understanding of underlying mountain topography can inform conservation priorities by revealing where shifting species stand to undergo area increases, decreases and bottlenecks as they respond to climate change.