| The term biodiversity refers to the wide range of | | | | more people place greater stress on the natural |
| organisms, plants and animals that exist within any | | | | environment, greater will be the loss of resources plant |
| given geographical region. That region may consist of | | | | and animal communities need to survive. |
| a plot of land no more than a few square meters or | | | | Maintaining biodiversity in a region and across the |
| yards, a whole continent, or the entire planet. Most | | | | planet is important for a number of reasons. First, |
| commonly, discussions of biodiversity consider all the | | | | some people argue that all species— because they |
| organisms that interact with each other in an extended | | | | exist—have a right to continue to exist in their own |
| geographical region, such as a tropical rain forest or a | | | | natural habitats, untouched by human development. |
| subtropical desert. Concerns about biodiversity are | | | | Second, humans depend on many of the plants and |
| relatively new. Only during the last quarter of the | | | | animals that make up an ecological community. For |
| twentieth century did scientists begin to appreciate the | | | | example, one-quarter of all the prescription drugs in the |
| vast number of organisms found on Earth and the | | | | United States contain ingredients obtained from plants. |
| complex ways in which they interact with each other | | | | And third, humans themselves benefit from the |
| and with their environments. Biologists have now | | | | interaction among organisms in a biologically diverse |
| discovered and named about 1.7 million distinct species | | | | community: plants help clean the water and air, provide |
| of plants and animals. As many as 50 million species, | | | | oxygen in the atmosphere, and control erosion. |
| however, are thought to exist. | | | | Biodiversity keeps the planet habitable and |
| Biodiversity in the tropics is of special interest since the | | | | ecosystems functional. |
| richness of species found there is so great. According | | | | One of the great issues in environmental science |
| to some estimates, 90 percent of all plant, animal, and | | | | today is how biodiversity can be preserved both in |
| insect species exist in tropical regions. At the same | | | | specific geographical regions and across the planet. |
| time, surveys of organisms in the tropics have been | | | | One proposal that has been made involves the use of |
| very limited. Those studies that have been conducted | | | | ecological reserves. Ecological reserves are protected |
| provide only a hint of the range of life that may exist | | | | areas established for the preservation of habitats of |
| there. As an example, one study of a 108-square | | | | endangered species, threatened ecological |
| kilometer (42-square mile) reserve of dry forest in | | | | communities, or representative examples of |
| Costa Rica found about 700 plant species, 400 | | | | widespread communities. By the end of the 1990s, |
| vertebrate species, and 13,000 species of insects. | | | | there were about 7,000 protected areas globally with |
| Included among the latter group were 3,140 species of | | | | an area of 651 million hectares (1.6 billion acres). Of this |
| moths and butterflies alone. | | | | total, about 2,400 sites comprising 379 million hectares |
| One reason for the growing interest in biodiversity is | | | | (936 million acres) were fully protected and could be |
| the threat that human activities may pose for plant and | | | | considered to be true ecological reserves. |
| animal species. As humans take over more land for | | | | Ideally, the design of a national system of ecological |
| agriculture, cities, highways, and other uses, natural | | | | reserves would provide for the longer-term protection |
| habitats are seriously disrupted. Whole populations may | | | | of all native species and their natural communities |
| be destroyed, upsetting the balance of nature that | | | | including terrestrial, freshwater, and marine (saltwater) |
| exists in an area. The loss of a single plant, for | | | | systems. So far, however, no country has put in place |
| example, may result in the loss of animals that depend | | | | a comprehensive system of ecological reserves to |
| on that plant for food. The loss of those animals may, | | | | fully protect its natural biodiversity. Moreover, in many |
| in turn, result in the loss of predators that prey on | | | | cases existing reserves are relatively small and are |
| those animals. As human populations grow, the threat | | | | threatened by environmental change, illegal poaching of |
| to biodiversity will continue to grow with it. And as | | | | animals and plants, and tourism. |