Butterflies and Wallace's Line: faunistic patterns and explanatory hypotheses within the south-east Asian butterflies

This paper reanalyses the distribution of the butterflies (Lepidoptera: Papilionoidea and Hesperioidea) in the south-east Asian region and adjacent mainland land masses using the most recent published information on distributions. The overall butterfly faunas of the Malay Peninsula, Borneo, Sulawesi, New Guinea and Australia are compared at the Family, Sub-family, Tribe, Genus and Species level. Distinct contrasts among these faunas arise only at the tribal level and below. Close linkages between the Malay Peninsula and Borneo, Australia and New Guinea are demonstrated at these taxonomic levels. The expected isolation of Sulawesi again emerges from the analyses. Detailed analyses of the Papilionidae, Nymphalidae-Danainae and Nymphalidae-Satyrinae are presented as both isopleth maps showing variation in species richness across the region, and in terms of Sorensen similarity values between adjacent islands (and other land masses). A set of discontinuities emerge in one, two or all three of these taxa which may be explained using an appropriate combination of tectonic, evolutionary and ecological mechanisms. Hypotheses are posed to explain each of the observed discontinuities and, where appropriate, further analyses are suggested.