Continental Biodiversity Research Articles

Evaluating trans-tethys migration: an example using acrodont lizard phylogenetics.

A phylogenetic tree for acrodont lizards (Chamaeleonidae and Agamidae) is established based on 1434 bases (1041 informative) of aligned DNA positions from a 1685-1778 base pair region of the mitochondrial genome. Sequences from three protein-coding genes (ND1, ND2, and COI) are combined with sequences from eight intervening tRNA genes for samples of 70 acrodont taxa and two outgroups. Parsimony analysis of nucleotide sequences identifies eight major clades in the Acrodonta. Most agamid lizards are placed into three distinct clades. One clade is composed of all taxa occurring in Australia and New Guinea; Physignathus cocincinus from Southeast Asia is the sister taxon to the Australia-New Guinea clade. A second clade is composed of taxa occurring from Tibet and the Indian Subcontinent east through South and East Asia. A third clade is composed of taxa occurring from Africa east through Arabia and West Asia to Tibet and the Indian Subcontinent. These three clades contain all agamid lizards except Uromastyx, Leiolepis, and Hydrosaurus, which represent three additional clades of the Agamidae. The Chamaeleonidae forms another clade weakly supported as the sister taxon to the Agamidae. All eight clades of the Acrodonta contain members occurring on land masses derived from Gondwanaland. A hypothesis of agamid lizards rafting with Gondwanan plates is examined statistically. This hypothesis suggests that the African/West Asian clade is of African or Indian origin, and the South Asian clade is either of Indian or Southeast Asian origin. The shortest tree suggests a possible African origin for the former and an Indian origin for the latter, but this result is not statistically robust. The Australia-New Guinea clade rafted with the Australia-New Guinea plate and forms the sister group to a Southeast Asian taxon that occurs on plates that broke from northern Australia-New Guinea. Other acrodont taxa are inferred to be associated with the plates of Afro-Arabia and Madagascar (Chameleonidae), India (Uromastyx), or southeast Asia (Hydrosaurus and Leiolepis). Introduction of different biotic elements to Asia by way of separate Gondwanan plates may be a major theme of Asian biogeography. Three historical events may be responsible for the sharp faunal barrier between Southeast Asia and Australia-New Guinea, known as Wallace's line: (1) primary vicariance caused by plate separations; (2) secondary contact of Southeast Asian plates with Eurasia, leading to dispersal from Eurasia into Southeast Asia, and (3) dispersal of the Indian fauna (after collision of that subcontinent) to Southeast Asia. Acrodont lizards show the first and third of these biogeographic patterns and anguid lizards exhibit the second pattern. Modern faunal diversity may be influenced primarily by historical events such as tectonic collisions and land bridge connections, which are expected to promote episodic turnover of continental faunas by introducing new faunal elements into an area. Repeated tectonic collisions may be one of the most important phenomena promoting continental biodiversity. Phylogenetics is a powerful method for investigating these processes.

The state of Australia's avifauna: a personal opinion and prediction for the new millennium

A consequence of the European colonization of Australia has been a significant loss of biodiversity: one in four mammal species is either extinct or threatened. In contrast, only one species of bird has been lost from the Australian continent and there is less concern for the survival of the Australian avifauna than for mammals. This is despite the fact that nearly one in five bird species is listed as threatened or of special concern. Moreover, a review of the status of Australian birds at local, regional, state and continental scales shows that the impact of Europeans on the avifauna is much greater than acknowledged. Over most of southern Australia entire avifaunas are threatened with extinction. When allowance is made for habitat loss and degradation, 30 to 90% of bird species across the continent have declined in abundance. The extent of this decline is that the survival of many bird species in the 21st Century is threatened. While a majority of birds in southern Australia has declined in abundance and/or distribution, others have increased. Parallel changes are proceeding in northern Australia. In terms of evaluating impact on the avifauna, an increase in numbers and a change in the composition of avian communities are as significant as the loss of populations and species. Both adversely affect patterns of continental biodiversity and are ecologically dysfunctional. Assuming that current trends continue, over the next century, significant components of the avifauna will be lost as populations proceed to extinction and the composition of avifaunas change at scales ranging from the local to the continental. The pattern of change in avian abundances, and the failure to anticipate or acknowledge the major losses of birds on the Australian continent, shows that conservation emphasis needs to shift from a species by species approach to the conservation of communities and entire avifaunas. Taken together, the scale of the changes in the distribution and abundance of Australian birds is an affirmation that present and projected patterns of human use of the Australian continent are not sustainable. Much needs to be done to reverse the decline of the terrestrial avifauna and achieve ecological sustainability in land use. The most urgent actions are to end the clearing of native vegetation, reduce grazing pressure, remove inappropriate fire regimes, control feral and native animals whose abundance threatens native species, and restore functional ecosystems, with an emphasis on native vegetation, to a minimum of 30% of the landscape. These need to be accompanied by an aggressive programme to improve water quality in fresh water habitats and restore environmental water flows, and the creation of a comprehensive, adequate and representative reserve system across the continent irrespective of land tenure. In the absence of such action, I predict that Australia will lose half of its terrestrial bird species in the next century.