Distributional pattern of plant species endemic to the Northern Territory, Australia

Abstract

The distributions of the 567 plant species considered to be endemic to the Northern Territory, Australia, were collated from a distributional database comprising about 600 000 records. Endemic species comprise a non-random taxonomic subset of all plants known from the Northern Territory. Because of substantial geographic disparity in collecting effort, we analysed geographic patterning of these endemic species by using both (1) actual records only and (2) interpolated ranges (minimum convex polygons). The geographic distribution of the number of Northern Territory endemic plant species was well predicted by a measure of topographic complexity and climate (particularly rainfall). The observed distributional patterning of endemic species was also influenced by survey effort, but this latter influence was substantially reduced by the use of minimum convex polygons. Both analyses revealed that there was a clear aggregation of endemic species in the 32 000 km2 of the sandstone plateau of western Arnhem Land. This ‘hotspot’ has been previously recognised in coarser-scale assessments of national and international centres of plant biodiversity. Our analysis concluded that 172 species are restricted to this plateau, and that the plateau comprised at least 90% of the distribution of a further 25 species. More broadly, 438 plant species are endemic to the northern part of the Northern Territory (the 316 000 km2 north of 16°S), a level of endemism that may match that of Cape York Peninsula and surpasses that of the Kimberley. The core area for Northern Territory endemic plants, the plateau of western Arnhem Land, is currently threatened, particularly by unfavourable fire regimes.

Biogeographic patterns on Kimberley islands, Western Australia

“…the Mitchell Plateau and Prince Regent River region) (Woinarski 1992;McKenzie et al 2009). Woinarski et al (2006) similarly demonstrated that endemic plant species richness in the Northern Territory was predicted by topographic complexity and rainfall, with higher richness in high-rainfall and topographically complex areas. As discussed above, the high rainfall areas support more monsoon rainforest which is an important resource for many species including numerous endemics (e.g.…”

The Nature of Northern Australia: its natural values, ecological processes and future prospects

“…Woinarski et al 2006a). It has also provided the necessary environment for the development of the richest rock art galleries in the world.…”

“…Some parts of Northern Australia have notably high species richness or endemism. The Kimberley supports about 2000 species of native plants (Wheeler et al 1992), of which about 300 are endemic ; Cape York Peninsula supports about 3000 species of native plants including at least 260 endemic species (Abrahams et al 1995;Neldner and Clarkson 1995); and the appreciably smaller (~30,000 km 2 ) plateau of western Arnhem Land includes at least 170 endemic plant species (Woinarski et al 2006a).…”

“…These include permanent or semi-permanent billabongs and waterholes along major rivers, and extensive ephemeral wetlands that fill seasonally or during major floods. Land are even richer (Abrahams et al 1995;Mackey et al 2001;Woinarski et al 2006a). …”

“…Isolation has sheltered these islands from many destructive processes that have detrimentally affected mainland species and environments. Many now contain plant or animal species no longer found on the mainland (Southgate et al 1996;Woinarski et al 2000aWoinarski et al , 2003 …”