Salt Creek Watershed Project
Although "biodiversity" is a new term for many people, ecologists think of it as the reformulation of well-known concepts. Biological diversity, or biodiversity for short, refers to the variety in the web of life on Earth. The fundamental "building block" of biological diversity is the species. However, the concept of species is a somewhat arbitrary classification to try to put order into a continuum of variation among individual living organisms. By international agreement, the term "biodiversity" refers to variety at three levels: the genetic diversity within species (whether or not this genetic variation is apparent); the diversity of species; and the diversity of ecosystems. Implicit here is the realization that different ecosystems contain different sets of species and ecosystem processes, and that the best way to protect species or the genetic diversity within species is to protect their ecosystems.
As much as an urban human would like to believe that he or she is self-sufficient and isolated from esoteric considerations of biodiversity, it is this diversity of life forms that constitutes much of our environment and makes it habitable. About 1.5 million life forms have been identified so far, and there are estimates that the real total is between five and 80 million. Most of the known species are in the tropics, which have much more biological diversity than temperate or cold climates.
What has given the issue of biodiversity its current preeminence is the growing realization that we are not doing enough; species worldwide are being eliminated at an extraordinary rate as a result of our demands on the planet, and entire ecosystems are disappearing even before we have a chance to inventory the species that are present. We have been managing our environment on a site-by-site, issue-by-issue basis, and we are now seeing the signs of our cumulative impact on the planet.