DISTRIBUTION OF BUTTERFLIES IN THE NEW WORLD 333 



America, from sea level in the south to 3,000-4,000 meters in the 

 north. It has a counterpart in the north, Pieris, which extends from 

 68° N. Lat. (at sea level) to 15° N. Lat. (at 2,000-4,000 meters). 

 The ranges of these two nominal genera are separated by low- 

 elevation barriers in Central America. There is good reason for 

 considering them to be congeneric, since the differences between 

 them are not greater than those between species within each group. 



The remaining genera of the Pierinae are all equatorial; only one, 

 Ascia, ranges north of the Tropic of Cancer. The altitudinal range 

 of some of the genera is narrow (less than 1 ,000 meters) , of others 

 wide (up to 4,000 meters). Catasticta ranges from 20° N. Lat. to 

 20° S. Lat., and at all elevations from sea level to 3,000 meters. 



The range of the Rhodocerinae is wider than that of the Pierinae 

 and is equivalent to that of the Pieridae as a whole. The genera are 

 divisible again into temperature-tolerance groups as is shown by the 

 histograms. 



Eurema is equatorial; it ranges to 30° N. Lat. and to 25° S. Lat., 

 and up to 3,000 meters in the central Andes. Phoebis is equatorial 

 but extends farther north than Eurema (to 35° N. Lat.,) although it 

 has a more limited altitudinal distribution. Anteos is also equatorial; 

 it extends north and south only to 25° and has a limited elevational 

 distribution (to 2,000 meters). Kricogonia is subtropical with a 

 range extending only from 10° to 30° N. Lat., at near sea level. This 

 is unusual in that most species or genera that inhabit the tropics 

 cover the entire tropical area from the Tropic of Cancer to the Tropic 

 of Capricorn with little in the way of further limitations. 



Colias is low-temperature dependent, as is shown by the histo- 

 gram. It ranges from 82° N. Lat. to 55° S. Lat., is present across the 

 equator at high elevations, but is absent in the low elevations in the 

 tropical regions and exists farther north and at higher elevations 

 than any other butterfly genus. The altitudinal range in North 

 America (to 5,000 meters) and in the Andes is as high as any or- 

 ganism can live. The range is broken by a gap of 5° latitude from 

 Guatemala to Venezuela and Colombia. 



Zerene resembles Colias in pattern of distribution, but usually 

 lives in warmer regions and at lower elevations. It exists only to 40° 

 N. Lat. and 30° S. Lat., is absent from lower elevations across the 

 equatorial regions and inhabits the middle-equatorial altitudes 

 (1,000-3,000 meters), in a zone intermediate between the hotter 



