Strangers in a strange land: ecology of the Australian colubrid snakes

Nine species of colubrid snakes occur in Australia, but they probably invaded that continent only recently compared to the endemic pythons, elapids and typhlopids. Most of the Australian colubrids are aquatic or arboreal species of tropical areas, congeneric or conspecific with Asian forms. Dissection of > 1400 specimens in museum collections provided information on body sizes, diets and reproductive biology. Males grew larger than females in Boiga and Stegonotus, but females were larger in the other genera. Dendrelaphis punctulata was primarily diurnal (especially in southern populations) but all other species tended to be crepuscular or nocturnal. Diets were diverse: the homalopsines fed mainly on fishes and crustaceans, whereas Tropidonophis ate anurans, Dendrelaphis anurans and lizards, and Boiga birds, lizards and mammals. Stegonotus consumed a variety of prey types, especially reptilian eggs. Diets of Boiga and Dendrelaphis showed strong geographic variation. Mean clutch or litter sizes ranged from 5.5-13.0, and were correlated with maternal body size in four species. Offspring size was highly correlated with mean adult body size interspecifically. Some colubrid species showed highly seasonal reproduction (e.g., Boiga), but Tropidonophis reproduced virtually year-round. Incubation periods and relative clutch masses were similar among species. The Australian colubrids include significantly higher proportions of aquatic and arboreal species than do either their Asian relatives, or the endemic Australian elapids and pythons. These characteristics may have facilitated the southward invasion of the colubrids from Asia to Australia. Diets of the Australian colubrids differ from those of sympatric elapids and pythons, but resemble those of Asian colubrids. Hence, the distinctive ecological characteristics of the Australian colubrids compared to the older lineages of Australian snakes reflect a combination of habitat-specificity due to limited migration corridors from Asia to Australia, and pre-existing dietary adaptations to Asian environments. Australian colubrids show a series of preaptations-mostly ecological specializations-rare among the older and more diverse ophidian lineages of Australia.

The Australian colubrids include significantly higher proportions of aquatic and arboreal species than do either their Asian relatives, or the endemic Australian elapids and pythons. These characteristics may have facilitated the southward invasion of the colubrids from Asia to Australia. Diets of the Australian colubrids differ from those of sympatric elapids and pythons, but resemble those of Asian colubrids. Hence, the distinctive ecological characteristics of the Australian colubrids compared to the older lineages of Australian snakes reflect a combination of habitat-specificity due to limited migration corridors from Asia to Australia, and pre-existing dietary adaptations to Asian environments. Australian colubrids show a series of preaptations-mostly ecological specializations-rare among the older and more diverse ophidian lineages of Australia.