Biological Diversity

Understanding Biological Diversity

In recent decades, our understanding of biological diversity has advanced enormously so that the simple tree of life of schoolchild days (two big trunks: one for plants and the other for animals with microbes at their base) has been replaced with something that represents a low spreading bush with only a couple of twigs toward one end representing plants, animals, and fungi. All the rest is an astonishing array of microorganisms, many with strange metabolisms and appetites dating to the early history of life on Earth and with potentially great value as nontoxic elements in industrial processes.

The diversity—termed “endless forms, most beautiful” by Charles Darwin—is awesome. Science has described about 1.7 million species since [Page 124]Linnaeus began the task in the 18th century, but there is no accurate sense of how many species remain to be discovered and described. In large degree, that is because exploring life on Earth has not risen to the level of recognized importance of discovering the subatomic particles, or space exploration, despite its direct relevance to human welfare and the fascination and excitement inherent in doing so. In addition, there is the complication that it is not easy to apply the definition of a species to microorganisms.

The total number of extant species remains an elusive number. Among widely accepted numbers are 3 to 5 million and 10 million, estimated in different ways by Baron Robert May of Oxford, of Oxford in the county of Oxfordshire. It could of course be higher, leading Edward O. Wilson to say we really do not know the number of species we share the planet with to an order of magnitude. Whatever it is, there is clearly a great frontier for exploring life on Earth.

Biological diversity is also a characteristic, in the sense that every ecosystem and biological community has both a characteristic species composition and species number. So, for example, a northeastern temperate forest in North America usually has somewhere between 20 and 30 species of trees, whereas a tropical rain forest in the Amazon has many hundred tree species.

This turns out to be very useful in environmental science and management. In the 1940s, freshwater ecologist Ruth Patrick determined that the number and kind of species in streams and rivers in the Middle Atlantic states reflected not only the natural physics and chemistry but also all the stresses from human activity on the watershed. In other words, biological diversity provides a direct measure of the sustainability of human activities within an ecosystem.

This “Patrick principle” applies to any kind of ecosystem and lies at the very heart of environmental science and management. In one sense, the reason is that by definition environmental problems affect living systems, and as a consequence biological diversity integrates all environmental problems. It makes it the perfect measure of course, but it also means that generically biological diversity is harder to conserve because it depends on addressing all environmental problems.

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