Historical ecology of sub-antarctic weevils (Coleoptera: Curculionidae): Patterns and processes on isolated islands

The Ectemnorhinus-group of weevils is endemic to the South Indian Ocean Province Islands of the sub-Antarctic region. Although small (36 species), it is the most diverse monophyletic arthropod taxon in the province. As such it is one of the few groups which allows comparisons of ecological and evolutionary patterns displayed by biotas on the extremely isolated sub-Antarctic archipelagos, with those exhibited by tropical or northern temperate biotas. Current information on habitat use, diet, assemblage structure and the evolution of the group is reviewed and compared with similar studies of tropical or temperate island biotas, as well as with current ideas on the ecology and evolution of island biotas. A recent phylogeny is used as a chronicle on which to base this historical account. The 36 species fall within six genera which have two major lifestyles, viz. angiosperm herbivory or cryptogam herbivory. These feeding habits constrain species in their habitat distributions on the islands and seem to have been a result of climatic forcing associated with Milankovitch cycles, rather than taxon cycles or pulses associated with competition in a centre of origin. At a regional level the influence of climate is pronounced, whereas at a local level the effects of interspecific interactions, or lack thereof, are marked. Circumstantial evidence favours between-island allopatry as the dominant speciation mode in the group, although sympatric speciation in historically young, angiosperm communities may have contributed to rapid diversification in the taxon. In general, the patterns and processes documented for weevils on these isolated islands agree closely with those found in biotas from other islands.