On Evolution

14. An American Naturalist’s Impressions on Australian Biodiversity

Biodiversity in the modern age is under threat, ultimately from pressures associated with human overpopulation. In this chapter, contrasts are drawn between how two similar yet very different continents may be facing conservation challenges related to human numbers. In , a symposium entitled “Biodiversity Conservation in Freshwaters” was held in Canberra, Australia. The speakers addressed root causes for the imperiled state of freshwater biodiversity in Australia , and the resulting management challenges. Australian wetlands and watersheds, already scarce, have come under assault in recent decades from increased water usage by humans and the introduction of exotic species. Speakers representing management agencies and academic units generally were saddened and alarmed by the decline of Australian biodiversity, and by a perceived inadequacy of governmental and societal responses to the problem. At the close of the conference, organizers asked the handful of biologists visiting from overseas for our initial reactions to the Australian conservation experience , and how the challenges might compare with those on our own continents. Here are some of my impressions. As first appreciated by Sclater and Wallace in the s, Australia and North America are two of the planet’s six primary biogeographic provinces. During the past  million years, Australia’s geographic isolation has promoted evolutionary radiations of many characteristic biotic groups, including marsupial mammals, corvidlike birds, and An American Naturalist’s Impressions on Australian Biodiversity 14 eucalyptus and acacia plants. Humans colonized Australia about , years ago, and this may have contributed to the extinction of much of the continent’s native megafauna (land animals weighing more than  kg) that began shortly thereafter. In North America, a similar mass extinction followed the much later arrival of humans there, about , years ago. Thus, people have long impacted indigenous biotas on both landmasses. Furthermore, after the arrival of Europeans on both continents in the past few centuries, the pace of environmental modification has accelerated tremendously and now threatens many kinds of creatures, both large and small. The conference kicked off my second three-week-long visit to Australia , the first having been  years earlier. Although brief, these trips included wildlife excursions through the eastern and central portions of the continent—New South Wales, Tasmania, Queensland , South Australia, and the Northern Territory (including Arnhem Land and the interior near Alice Springs). On both occasions, I fell in love with Australia’s rich native fauna and flora, the country’s relatively unspoiled natural landscapes, and, most of all, the uncrowded feel of the continent. To a natural historian born and raised in the more congested United States, my first impression is that Australia’s land and nature are about as untrammeled as those in North America may have been approximately  years ago—impacted and far from pristine, but not yet overwhelmed by human presence. Of course, Australian biodiversity is under heavy siege from human activities. With regard to aquatic habitats, conservation issues highlighted at the conference were the urgent need to protect Australia’s imperiled river drainages and aquifers, to properly identify and manage freshwater biodiversity on regional as well as local scales, and to control the introduction and spread of nonindigenous species such as carp fish, which often wreak havoc on native wildlife and ecological processes. Problems also abound in the terrestrial realm. For example , one response to the limited availability of agricultural land in Australia has been to forage cattle across much of the continent, and this has transformed the land. Feral and exotic species such as cats,  On Evolution rats, mice, goats, rabbits, and foxes also have had a huge impact by predating or competing with native wildlife. Some Australian scientists have been especially active in promoting the release of genetically modified (GM) organisms as a potential means to control exotic pests. For example, GM viruses have been engineered to serve as a vector for transgenes that induce rabbit sterility. Despite the serious scientific and social challenges that conservation efforts in Australia clearly face, I couldn’t help but conclude, during the Fenner Conference and in my travels, that the Australian natural environment and its native flora and fauna remain in far better shape than those in most of North America. In much of the continental United States, remnants of nature tend to be confined to small pockets in a human-dominated landscape, whereas in Australia, nature more often tends to be the basal matrix in which islands of human modification are embedded. I...