Invasive species: a costly catastrophe for native biodiversity

Species introduced from outside their natural range can be an economic boon, because they often seem to do better in their new home than in their place of origin. For example, various species of eucalyptus from Australia are widespread in Southeast Asia, China, India, California, and various parts of Africa, and South Africa's colourful proteas bless many of the world's gardens. Further, 'natural' is becoming an increasingly obsolete concept, as virtually all ecosystems have a strong and increasing anthropogenic component. People are designing the kinds of ecosystems they find congenial. The great increase in the introduction of aliens that people are importing primarily for aesthetic reasons - ornamentals to make their gardens more attractive - often leads to a net increase in species richness in their destination. It is quite likely, for example, that many parts of the world have far more species now than ever before, though this great increase of species numbers is usually at least partly at the expense of indigenous species (and thus reduces global species diversity). But a species introduced for noble economic or aesthetic objectives may escape into the wild, invading native ecosystems with disastrous results : they become alien invasive species (AIS). Greatly improved transport that enables traders to move goods around the world quickly is providing ideal opportunities for the accidental introduction of AIS, ranging from zebra mussels to disease-carrying mosquitoes to bacteria and viruses. It appears that few purposeful introductions have been accompanied by a careful consideration of the full costs involved. When the costs have become apparent, they can be astronomical; one study in the United States estimates that costs associated with alien species amount to some US$136 billion per year, and the recent disastrous fires in South Africa appear to be at least partly due to the spread of AIS. These costs usually must be paid by someone other than those who sponsored or promoted the introduction - often the general public. Decision-makers need to invest more in assessing the potential impacts before allowing introductions and to incorporate more biosecurity measures once the species has been introduced. Accidental introductions by definition are not exposed to a prior cost-benefit assessment, but assessments of the costs of such introductions can justify increased budgets to control and limit such accidental introductions. AIS issues also link to other issues of major policy concern, such as biotechnology, global trade, water, human health, and climate change. The Convention on Biological Diversity offers an important opportunity for addressing the complex global problems of introduced species through improved international cooperation.