Tropical niche conservatism and the species richness gradient of North American butterflies

摘要: ABSTRACTAim We explore the potential role of ‘tropical conservatism hypothesis’in explaining butterfly species richness gradient in North America. Itsapplicability can be derived from tropical origin butterflies and thepresumed difficulties evolving cold tolerance required to permit thecolonization permanent occupation temperate zone.Location America.Methods Digitized range maps for north Mexico were usedto map all species, with distributions Tropic ofCapricorn (Extratropicals), that also occupy tropics (Tropicals).A phylogeny resolved subfamily was used geographical pattern ofmean root distance, a metric evolutionary development assemblages.Regression models general linear examined environmental correlatesof overall Extratropicals vs. Tropicals, patterns summer vs.winter, northern southern America.Results Species more basal subfamilies dominate south, whereas morederived clades north. There is ‘latitudinal’ inCanada/Alaska, conterminous USA primarily varieslongitudinally. Overall associated broad- mesoscaletemperature gradients. The Tropicals strongly withtemperature distance winter population sources. ofExtratropicals most correlated glacialretreat since recent Ice Age, positivelyassociated temperatures mountains presence offorests but negatively broad-scale temperature gradient.Main conclusions hypothesis provides possibleexplanation complex structure gradient. TheCanada/Alaska fauna comprises temperate, boreal tundra arenevertheless constrained by climates limited vegetation, coupled withpossible post-Pleistocene recolonization lags. In areconstrained as well distancesin summer, temperate-zone groups are richer cooler inmountains forests, where conditions suitable diapause.The evolution key both ecologicalpatterns.KeywordsButterflies, tolerance, diapause, diversity gradients, latitudinal gradients,niche conservatism, America, Rhopalocera, gradients,tropical hypothesis.