Species diversity is
the most familiar type of biodiversity. In this catagory, every group
of organisms that can reproduce among itself is recognized for
its environmental niche.
Although it would be nearly impossible to count each one, most
scientists estimate that there are at least 10 million unique species
of organisms on Earth.
Today, scientists have named and identified more than 1.75 million
species but believe this is just 20 percent of the
total existing species. We will probably never be able to accurately
calculate the total number species are constantly going extinct, more quickly
than we can learn about them. (Encarta, "Biodiversity")
Many local environmental organizations seek to preserve the environment
by saving one species at a time. This by itself is insufficient,
because species are all interrelated. The outcome of one species
determines life for all others in its ecosystem.