Magnitude and Overview of Global Biodiversity Loss
Jeffrey A. McNeely
Chief Scientist
IUCN-The World Conservation Union
The most comprehensive view of global biodiversity loss is summarized in the
Millennium Ecosystem Assessment, which was carried out between 2001 and 2005 by over 1300 scientists from around the world. The MA found that changes in biodiversity due to human activities were more rapid in the past 50 years than at any time in human history; species loss was about 1000 times higher than the background rate. Perhaps worse, the drivers of change that cause biodiversity loss and lead to changes in ecosystem services are either steady, show no evidence of declining over time, or are increasing in intensity.
While attention to biodiversity loss has tended to be focused at the species level (for example, through the IUCN Red List of Threatened Species), and species loss continues to be the most dramatic expression of biodiversity loss, loss at other levels may be even more significant. Ecosystem loss, for example when a mangrove is converted to a shrimp pond, can have profound effects on human welfare as well as on the functioning of natural ecosystems. The replacement of a species-rich natural forest with a single-species plantation of rubber, oil palm, eucalyptus, pine or acacia leaves an impoverished ecosystem that supports many fewer species than the ecosystem replaced.
Below-ground biodiversity is also beginning to receive far more attention, and evidence is accumulating that the more intensively used lands suffer the most rapid loss of belowground biodiversity, which in turn leads to a significant reduction in important ecosystem services.
At the genetic level, many agro-ecosystems are becoming increasingly simplified, with far fewer cultivars reaching the market. In the UK, for example, some 2,000 species of apples are grown, but most supermarkets sell only a few varieties imported from other countries. The loss of genetic diversity among agricultural crops is of growing concern as increasing pressures are put on agricultural systems. These include changing climate, increasing demand, new technologies, and many others; all of these require enhancing biodiversity as a means of enabling agro-ecosystems to adapt to changing conditions.
Another serious threat is invasive alien species. While agriculture in virtually all parts of the world depends largely on species that originated elsewhere (examples include wheat and chickens in North America, soy beans and cattle in Brazil, cassava and cacao in
Africa, potatoes and tomatoes in Europe, and corn and rubber in Asia), these species are not invasive in the sense considered by the Convention on Biological Diversity. But in virtually all parts of the world, international trade that is an inevitable part of globalization has also brought in new species that have spread far beyond their original purpose, or which arrived accidentally and quickly spread to become pests. These can often cause significant damage to both agro-ecosystems and the rest of biodiversity. The

spread of Africanized bees through the Western hemisphere, water hyacinth in Asia and
Africa, and diseases such as West Nile virus and avian influenza, are dramatic examples of this problem.
Governments have agreed to stop the rate of loss of biodiversity by 2010. The
Convention on Biological Diversity (which has been ratified by 188 countries) defines biodiversity loss to be “the long-term permanent qualitative or quantitative reduction in components of biodiversity and their potential to provide goods and services, to be measured at global, regional and national levels”. This definition implies that biodiversity loss can result if the diversity per se is reduced, for example, through the extinction of some species, or if the potential of the components of diversity to provide a particular service is diminished (for example, through unsustainable harvest).
Biodiversity is threatened from many directions. Particularly significant is the conversion of diverse ecosystems into greatly simplified ecosystems that are intensively managed to provide narrow, though valuable, benefits to people. Such ecosystems tend to be much more vulnerable to disruption, and often require expensive external inputs to maintain their productivity. Efforts to ensure that agro-ecosystems maintain diversity and enhance, or at least maintain, wild aspects of biodiversity are expanding throughout the world.
Organic agriculture, ecoagriculture, agro-ecology and other such terms are recognizing the importance of biodiversity for maintaining agricultural productivity; many of these approaches will be addressed by other speakers at this Symposium