| Abstract: | Abstract The possums and gliders of Australia and the lemurs of Madagascar are ideally suited for investigation of radiation and convergence in arboreal mammal communities because of their long history of independent radiation in similar biophysical environments. Possum and glider communities at 22 sites in Australia and lemur communities at 18 sites in Madagascar were compared to evaluate patterns of community and species convergence in two shared habitats (evergreen and deciduous monsoon rainforests) and three derived habitats (Australian eucalypt forests and heaths, and Malagasy thorn scrubs). Arboreal mammals were classified into five dietary guilds for comparison of community structure and species adaptation. There is little evidence of convergence in trophic structure at the community level, but strong evidence of convergence in dietary adaptation at the species and niche level. Malagasy rainforest communities were characterized by a higher proportion of frugivore-folivores, and Australian rainforest and moist eucalypt communities by a higher proportion of folivores and folivore-frugivores. Possum and glider communities in temperate eucalypt forests and heaths supported a higher proportion of nectarivores and exudivores. Overall species richness was significantly higher in Madagascar. Four hypotheses are erected to account for these differences. The relative scarcity of frugivores in Australian evergreen rainforests is accounted for by the predominance of bird-dispersed fruits, and fruiting phenologies unsuitable for mammal exploitation and dispersal. Higher folivore diversity in Australian evergreen rainforests is associated with a more pronounced seasonal shortage of edible fruits and new leaf, which has increased dependence on mature leaf. Folivore species richness is greatest in Australian moist eucalypt forests where structural complexity, sustained by serai responses to wildfire, permits a high level of vertical segregation. Increased nectarivory and exudivory in Australian temperate eucalypt forests and heaths is associated with Mediterranean winter rainfall regimes, which permit year round exudate production, and not with the absence of nectar feeding bats as previously supposed. A lower overall species richness in Australian rainforests is attributed to a longer history of contraction and fragmentation by anthropogenic fires (monsoon rainforests) and Pleistocene climatic change (tropical evergreen rainforests). A high degree of convergence is apparent between genera occupying folivore and wood gouging niches, in terms of gastrointestinal morphology (e.g. Pseudocheirus-Lepilemur) and dental morphology (e.g. Dactylopsila-Daubentonia). Divergences are most apparent in adaptations associated with frugivory, including larger body size, diurnality, and bipedal suspension and leaping modes of locomotion (in Eulemur spp.). This study highlights the importance of founding effects, competition from other vertebrate taxa, coevolution between animals and their food plants, and differences in biophysical environments, as determinants of mammalian radiation and convergence. |
