• Border fence;
  • endemic species;
  • northern Mexico;
  • range margins;
  • southwestern US;
  • species range maps;
  • threatened species;
  • transboundary conservation


Aim  Humans have dramatically transformed landscapes along the US–Mexico border. We aim to assess the risk of barriers that may significantly impede animal migrations within this ecologically sensitive region.

Location  United States and Mexico.

Methods  We examined the intersection of current and possible future barriers along the border with the geographic ranges of 313 amphibian, reptile and non-volant mammal species. We considered the areas of intensive human land use and ∼ 600 km of pedestrian fence as current barriers along the border. We evaluated the impacts of two scenarios of dispersal barriers – continuation of existing and construction of new barriers – and identified species vulnerable to global and local extinction.

Results  Among the species most at risk from current barriers are four species listed as threatened globally or by both nations, 23 species for which the larger of their two national subranges is < 105 km2 and 29 species whose ranges cross the border only marginally. Three border regions, California, Madrean archipelago and Gulf coast, emerge as being of particular concern. These regions are characterized by high overall species richness and high richness of species at risk from existing barriers and from construction of potential new barriers.

Main conclusions  New barriers along the border would increase the number of species at risk, especially in the three identified regions, which should be prioritized for mitigation of the impacts of current barriers. The species we identified as being potentially at risk merit further study to determine impacts of border dispersal barriers.