Conserving Biological Diversity

Article excerpt

The incredible stew of genes, species, and ecosystems that both defines and sustains life on earth is deteriorating at a frightening rate. Here is a strategy for stemming the losses.

Biological diversity--complex beyond understanding and valuable beyond measure--is the total variety of life on earth. No one knows, even to the nearest order of magnitude, how many life forms humanity shares the planet with: Roughly 1.4 million species have been identified, but scientists now believe the total number is between 1O million and 80 million. Most of these are small animals, such as insects and mollusks, in little-explored environments such as the tropical forest canopy or the ocean floor. But nature retains its mystery in familiar places as well--even a handful of soil from the eastern United States is likely to contain many species unknown to science.

Despite the vast gaps in knowledge, it is clear that biodiversity--the ecosystems, species, and genes that together make life on earth both pleasant and possible--is collapsing at nothing less than mind-boggling rates. Difficult as it is to accept, mass extinction has already begun, and the world is irrevocably committed to many further losses. Harvard biologist Edward O. Wilson estimates that at a minimum, 50,000 invertebrate species per year--nearly 140 each day--are condemned to extinction by the destruction of their tropical rainforest habitat. Large creatures as well as small are vanishing: deforestation condemns at least one species of bird, mammal, or plant to extinction daily.

Moreover, biological impoverishment is occurring all over the globe. Ecosystems with fewer species than rainforests have, such as islands and freshwater lakes, are probably losing even greater proportions of their varied life forms. Genetic varieties within species and entire natural communities are also disappearing, likely at rates greater than the extinction of species themselves.

Protection of wildlands will be the top priority of any meaningful strategy to safeguard the world's biological heritage. True protection of these ecosystems alone will require sweeping changes in the way humanity views and uses land and a commitment to limit the amount of the earth's bounty that society appropriates to itself. But in order to staunch the massive bleeding of life from the planet, humanity must learn not only to save diversity in remote corners of the world but also to maintain and restore it in the forests and waters that we use, and in the villages and cities where we live.

Why should disappearing beetles, plants, or birds concern us? To biologists, and to many others, the question hardly needs asking: A species is the unique and irreplaceable product of millions of years of evolution, a thing of value for scientific study, for its beauty, and for itself. For many people, however, a more compelling reason to conserve biological diversity is likely to be pure self-interest: Like every species, ours is intimately dependent on others for its well-being.

Time after time, creatures thought useless or harmful are found to play crucial roles in natural systems. Predators driven to extinction no longer keep populations of rodents or insects in check; earthworms or termites killed by pesticides no longer aerate soils; mangroves cut for firewood no longer protect coastlines from erosion. Diversity is of fundamental importance to all ecosystems and all economies.

Life on the Brink

Biodiversity is commonly analyzed at three levels: the variety of communities and ecosystems within which organisms live and evolve, the variety of species, and the genetic variety within those species themselves. The degradation of whole ecosystems, such as forests, wetlands, and coastal waters, is in itself a major loss of biodiversity and the single most important factor behind the current mass extinction of species.

Home to at least half the planet's species, tropical forests have been reduced by nearly half their original area, and in 1990 deforestation claimed 17 million hectares (one hectare equals 2. …