Abstract
Biodiversity includes the diversity of genes, species and ecosystems on earth, but here for convenience I focus on species loss and ecosystem degradation. At least five times since life evolved on Earth, mass extinction events have taken place, involving the extinction of vast numbers of species (Futuyma, 1998). Perhaps over 95 per cent of all species that have lived on earth are now extinct (Rosenzweig, 1995), and a ‘background’ level of extinction is to be expected regardless of human activities (Macleod, 2002). Today, however, relevant indices point to our being on the cusp of the sixth great extinction event, this one distinguished by the fact that it is caused primarily by human activities (Leakey and Lewin, 1995). Around one in eight of the world’s bird species, a quarter of its mammals, and one in three amphibians are threatened with extinction (Baillie, Hilton-Taylor and Stuart, 2004). The extent and rapidity of anthropogenically-induced recent and threatened extinctions far outstrips the rate of evolution of new species and threatens fundamental ecosystem processes which maintain all life on earth. Many would view the extinction of other species as alarming per se. However, threats to biodiversity are also threats to humans: to the provision of materials and services for life, health, security and wellbeing. Biodiversity provides food, medicine, fuel and building materials. Biodiverse ecosystems help filter water, control flooding, regulate climate, decompose waste, generate soil and pollinate crops.