Patterns in the geographical range sizes of ectotherms in North America

The distributions of homeothermic mammals and birds in continental North America show a distinct pattern in the configuration of their geographical ranges. Smaller ranges tend to be elongated north-south while larger ranges tend to be elongated east-west. To examine the generality of this pattern in ectotherms, we analyzed the distribution on continental North America of 139 species of mosquitoes, 164 amphibians, and 221 reptiles. Unlike birds and mammals, small ranges of ectotherms were not elongated north-south and the small ranges of snakes were elongated east-west. The distribution of ectotherms with small ranges does not appear to be affected by the major topographic features of North America which tend to run north-south. Like birds and mammals, large ranges of mosquitoes and reptiles but not amphibians are elongated east-west. The east-west orientation of mosquitoes with large ranges is not attributable to the three largest genera in North America taken singly, Aedes, Culex, or Anopheles, but appears only when all genera are pooled. The east-west orientation of reptiles with large ranges is attributable to turtles and snakes but not lizards. Climatic zones may thus affect the distribution of mosquitoes, turtles, and snakes with large ranges but are not the major determinants of range dimensions among ectotherms in general. Received: 1 September 1997 / Accepted: 8 February 1998