Arthropods of Australia’s subtropical and tropical rainforests: rich and unique hotspots of biological diversity?

Abstract

The tropical and subtropical rainforests of eastern Australia are a major component of the Forests of East Australia global hotspot. Australian rainforests are maintained orographically and are embedded within vast tracts of pyrogenic open forest and woodland. Australian tropical and subtropical forests stretch over 24° of latitude from Cape York, Queensland, to south of Sydney, New South Wales. Since European colonization in 1788 these rainforests have been reduced in extent by about 30%. The most abundant and functionally significant animal species within these forests are arthropods. These have attracted the attention of western science since before formal colonization. Through the twentieth century this focus increased and comparative biogeographic studies began to emerge. Some taxa have received much more attention than others. Selected butterflies and beetles plus economically important species stand out in this respect. From the late 1980s mass sampling approaches developed. Recent research foci have included tropical and subtropical elevational transects, latitudinally diverse multi-method one-hectare surveys, and use of canopy knockdown as a way of sampling the canopy. Important and distinct patterns reflecting latitude, altitude and vertical position have emerged. A focus on moths in remnant and elevational studies has led to the identification of indicator sets of species which may be most useful for tracking the impacts of environmental degradation and global warming. Arthropods are increasingly being nominated on lists of rare, threatened and endangered species; a range of species of insects, particularly butterflies, have been so identified in Australia but few of these are rainforest species. The vulnerable Richmond Birdwing butterfly, a species of subtropical rainforests, has become an icon of how recovery methods can be applied to invertebrate species. Regarding the entire rainforest community—microbiota, plants, vertebrates and invertebrates—as the ‘object’ to be conserved is an essential and much more realistic mindset for future conservation efforts. Most of Australia’s tropical and subtropical rainforests are held in National Parks and they are defining features of two of Australia’s largest World Heritage Areas. Growing impacts of global warming means they cannot be regarded as ‘safe’ from a conservation point of view. Increasing frequency of wildfires impinging upon rainforest areas is having a devastating effect on some of these fire-sensitive forests.Implications for insect conservationMost of Australia’s tropical and subtropical rainforests are held in National Parks and they are defining features of two of Australia’s largest World Heritage Areas. Nevertheless the growing impacts of global warming means they cannot be regarded as ‘safe’ from a conservation point of view. Increasing frequency of wildfires impinging upon rainforest areas is having a devastating effect on these fire-sensitive forests. Regarding the entire rainforest community—microbiota, plants, vertebrates and invertebrates—as the ‘object’ to be conserved is an essential and much more realistic mindset for future conservation efforts.