POPULATION AND BIODIVERSITY
umankind's greatest assault on the planet's biodiversity comes from the destruction of ecosystems. These are not merely the home to the world's species, they are also the providers of numerous "ecological services" without which life on the planet could not persist. [Add]
A conventional measure of biodiversity, the counting of species, produces some remarkable conclusions. Most of the world's known species are contained within an extremely small area. An estimated 44 percent of all plant species and 35 percent of all land vertebrates live exclusively within just 25 "hotspots" that together make up only 1.4 percent of the land surface of the globe, an area roughly the size of Greenland . Most of these hotspots are within the tropics and particularly in tropical rainforests, where biologists estimate that half the world's species live.
There are many reasons for this concentration. Species proliferate best where there is more solar energy to drive natural systems (hence in the tropics); where ecosystems have developed that provide a huge variety of habitats (such as the many layers of a tropical rainforest or the nooks and crannies of a coral reef); or where isolation creates conditions in which, over millions of years, evolution takes a unique course . Thus many islands have species of plants, insects and vertebrates, especially birds, that are found nowhere else. A tenth of the world's bird species evolved in an isolated island environment.
This "endemism" is especially pronounced on large islands cut off for millions of years, such as Madagascar (which has more than 6 000 unique species of flowering plants) and Australia (home of marsupials). But the isolation that creates such biodiversity also makes those species particularly vulnerable to outside interference, both because of their limited spread and because they have little resistance to disease or pests from outside. Birds endemic to individual islands make up more than 80 percent of known species extinctions.
Other hotspots of endemism were, in effect, ecological islands in past eras. Many patches of especially diverse tropical forest, for instance, are ancient forests that survived through the colder and often drier conditions of the ice ages. During those periods evolution pursued its own individual course in forest islands surrounded by savannah. One such "fossil forest" is the Korup rainforest in Cameroon. [Add]
One approach to conservation is to concentrate on protecting these hotspots as ecological fortresses . But this runs the danger of ignoring the many other functions of natural ecosystems, particularly in their provisions of vital and diverse environmental management functions.
Ecosystems break down pollutants, purify dirty water, and store and cycle nutrients. They thus maintain chemical equilibrium in both ocean waters and the atmosphere. They create and regenerate soils and regulate rates of erosion. They sustain insects that pollinate most of the world's crops, provide free pest control and disperse seeds . They even help create rain. Half the rainfall in parts of the Amazon basin swiftly evaporates from tree leaves to create rain in the interior .
Many of the services offered by genetic, species and ecosystem biodiversity -- whether directly supplied food and medicines, genetic resources or wider environment management services -- could not be replaced by human structures or management systems. But because these benefits are not traded in the marketplace, they carry no price tag and can easily be ignored until it is too late . If they were effectively valued and took their place within the prevailing market system, they would be cherished as much as a share portfolio or factory. But since they are not, they are constantly open to being squandered in the name of short-term profit. [Add]
Even single species could dramatically change the appreciation of natural resources often deemed by governments as little better than wasteland. When a successful drug against childhood leukemia was developed from the rosy periwinkle, a plant found on the rainforest island of Madagascar, the royalties during the period when the drug came under patent protection exceeded US$100 million, but none got back to the people of the island . Had it done so, the incentive to protect the forests in the interest of finding new pharmaceuticals would have been underlined. Nobody would destroy a laboratory responsible for such a cash return. [Add]
Signatories to the 1992 Convention on Biological Diversity have pledged to develop property rights for natural resources to help protect biodiversity, but there is a long way to go. Generally, governments only seem to recognize the environmental management services provided by natural ecosystems when, through negative impacts, they actually fail, causing such problems as desertification, floods and mudslides, "red tides" of toxic algae and coastal erosion.
Protecting biodiversity and the environmental services that ecosystems provide will require not only the creation of protected havens for wildlife, but a much more sophisticated management of entire landscapes, integrating ecological services within largely human-dominated environments. In heavily populated regions such as much of Europe, this is effectively the only viable approach. But increasingly it will also be true of tropical landscapes, where human rights often have to be integrated with environmental protection.
Land demands in the tropics mean that surviving natural forests can rarely be fenced off without damaging the livelihoods of people who harvest their fruit, nuts, medicinal plants and bushmeat. Many believe that such uses need to be promoted and sustained -- along with other profitable activities from rubber-tapping to ecotourism, sustainable timber harvesting to trophy hunting -- if the forests are to survive rather than being converted to other uses.
On a crowded planet, some protected areas will retain their place as reservoirs of biodiversity. But the hardest challenge -- to preserve both species and the ecological services that sustain the Earth -- will be to find room, and a profitable role, for nature in managed landscapes where people, too, can live and prosper. [Add]