Butterfly biogeography and endemism on tropical Pacific Islands

Butterfly distributions on 26 tropical Pacific archipelagos were analysed to examine the effects of geography on diversity and endemism. The total butterfly fauna for each archipelago was divided into continental (found also on continental areas), Pacific (found within more than one archipelago but not ourside of the study area), and endemic species (restricted to a single archipelago). Numbers and proportions of each species were related to eight geographic variable by stepwise multiple linear regression analysis. Total area of an archipelago and distance from other land masses were important predictors of the number of species within an archipelago. Proportions of butterfly species in each category were related differently to the geographic variables, with endemism being promoted by the number of large islands within an archipelago. Relative to birds, butterflies have been less successful in colonizing remore archipelagos and have much lower levels of endemism. Even if colonization is successful, butterflies speciation may be constrained by the mechanics of coevolution with available host plants.