Aim We explore the potential role of the 'tropical conservatism hypothesis' in explaining the
butterfly species richness gradient in North America. Its applicability can be derived from the
tropical origin of butterflies and the presumed difficulties in evolving the cold tolerance
required to permit the colonization and permanent occupation of the temperate zone.
Location North America. Methods Digitized range maps for butterfly species north of Mexico
were used to map richness for all species, species with distributions north of the Tropic of …