Ice bridging as a dispersal mechanism for Arctic terrestrial vertebrates and the possible consequences of reduced sea ice cover

Abstract

The dispersal abilities of terrestrial mammals are severely constrained by water crossings, resulting in islands generally supporting less diverse mammal faunas than similar continental areas. In ice-affected Arctic regions, seasonal or permanent ice cover provides a bridging mechanism for dispersal, allowing water gaps to be crossed more rapidly and with less energy cost than is entailed in swimming. Consequently, islands that might be out of reach if waters were open become much more readily colonised in the presence of ice. We reviewed the distribution of terrestrial mammals on selected islands throughout the Arctic and analyse historical data for several sites in the Canadian Arctic where mammal populations have undergone extirpation and re-colonisation. We use these data to assess the value of ice for the dispersal of Arctic terrestrial mammals. Given observed dispersal distances we estimate the likely impact of future ice reduction on island faunas. We predict that, as ice cover duration shortens, immigration will decline leading to increased extinctions of island populations and potentially, in the long-term, local genetic differentiation. The eventual disappearance of ice bridges, preventing the immigration of southern species, may leave certain arctic archipelagos as the last refuge for typical Arctic mammals.