The biodiversity crisis in arid Australia
In the 200 years following the first European incursions into arid Australia, the heart of the continent has undergone many changes. Vast areas are used for livestock grazing, experience broadscale wildfires and support populations of introduced herbivores and predators; availability of surface water has also been increased via extraction from ground water sources. Over this period of change, 14 species of mammals, 10 species of other vertebrates and about 20 species of plants have disappeared. At least 52 species of vertebrates and over 100 plants are threatened with extinction in future. New challenges to the biota include expanding populations of feral camels, expansion of water sources into currently dry refugia, diversion of ephemeral waters for crops (cotton), and the omnipresent spectre of climate change.
Using data from a long-term (17-year) study in the Simpson Desert, I discuss the difficulties of sampling biodiversity in environments where many biota are rare and cryptic, and where spatial and temporal variation in productivity is extreme. Vertebrate diversity is affected strongly and negatively by drought and wildfire, especially in the presence of introduced predators, but increases after rain. Facilitatory interactions can also boost biodiversity in local areas, but occur only after productivity thresholds have been tripped. Simple state-and-transition models are proposed to explain patterns of biodiversity change and to identify the major processes that affect it.