Biogeography of Australian monsoon rainforest mammals: implications for the conservation of rainforest mammals

Abstract

Monsoon rainforests form an archipelago of small habitat fragments throughout the wet-dry tropics of northern Australia. According to the definition of Winter (1988) the current monsoon rainforest mammal assemblage contains only one rainforest specialist mammal species (restricted to Cape York Peninsula), and is dominated by eutherian habitat generalists (murids and bats) that mostly occur in surrounding savannah habitats. The mammal assemblages in monsoon rainforests across northern Australia (Cape York Peninsula, Northern Territory and the Kimberley) are essentially regional subsets of the local savannah and mangrove mammal assemblages, and consequently share only a limited number of species in common (most of which are bats). The lack of rainforest specialists in northwestern Australia is thought to be due to: (i) the lack of large tracts (> 1 000 ha) of monsoon rainforest habitat; (ii) the possible substantial contraction of these habitats in the past; and (iii) the limited extent of gallery rainforests, such rainforests being important habitats for rainforest mammals in South American savannahs. Unfortunately it is not possible to identify the threshold of habitat area required to maintain populations of monsoon rainforest specialist mammal species because of an impoverished fossil record pertaining to the past spatial distribution of monsoon rainforests. The implications of the lack of a specialist mammal fauna in Australian monsoon rainforests for the future of heavily fragmented tropical rainforests elsewhere in the world is briefly discussed. It is concluded that the analogy of habitat fragments to true islands is weak, that rainforest plant species are less vulnerable to local extinction than mammals, that the loss of mammal rainforest specialists may not result in a dramatic loss of plant species, and that corridors of rainforest may be critical for maintenance of rainforest mammal assemblages in areas currently subject to forest clearance.