In terms of species richness only, how much biodiversity exists? Various biologists have made widely different estimates for the number of species on Earth, ranging from 2 million to 100 million species. Yet in about 200 years of cataloging, scientists have named and described about 2 million species.

Because of the frequency and ease with which new species are discovered, scientists acknowledge the likelihood that there are many undescribed species. For example, in recent years, several new species of primates were discovered in Madagascar, and an entirely new order of insects was recognized. In 1982, biologist Terry Erwin announced that his team had studied all of the species of insects in one kind of tree in a tropical rain forest. They counted 1,200 beetle species, 163 of which seemed to inhabit only that one kind of tree.

Our knowledge of smaller organisms and organisms in remote or extreme locations is especially poor. Scientists must use innovative approaches to find and describe these lesser-known organisms. For example, they may build robotic vehicles to explore remote and extreme environments, such as caves, volcanoes, hot springs, and deep sea trenches. It seems that everywhere they look, scientists find new varieties of organisms.

Valuing Biodiversity

Biodiversity provides important benefits to people. For example, thousands of plant and animal species can serve as food. Trees provide wood for homes and fuel. Many species are sources of medicines and useful chemicals. Undiscovered species may someday supply other benefits. And ecosystems recycle human wastes, including CO2. Writing about such benefits, biologist E. O. Wilson stated, "Biological diversity is the key to the maintenance of the world as we know it."

Some people think that organisms and ecosystems are important for reasons other than their use to humans. These opinions may be based on moral, aesthetic, or religious beliefs that are beyond the scope of biology. People may value biodiversity for multiple reasons.

Estimating Microscopic Diversity

Materials microscope, dissecting scope, 50 mL sample of pond water Procedure Gently stir the pond water. Place one drop of the pond water on a microscope slide. Examine the slide under the dissecting scope and under the microscope at low magnification. Try to find as many different types of organisms as possible. Quickly draw or describe each one. Make a tally of the total number of unique organisms you find.

Analysis Compare your total and your descriptions with those of others in your class. How many unique kinds of organisms might there be in the total sample of pond water?

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