The word biodiversity is a contraction of the phrase "biological diversity" and was first coined in 1985 by Walter Rosen of the National Research Council as a title word in a seminar he was organizing to discuss biological diversity. Biodiversity includes all inherited information contained across all levels of variation, from genetic variation contained in individuals that then make up populations of species that form communities inhabiting ecosystems. Biodiversity is simply the variety of life on Earth, but its importance to global ecology has made it one of the most important concepts in modern science.
Because biodiversity cuts across different levels of organization it is often useful to focus on a particular type of biological diversity.
- Species diversity is a measure of how many different species are present in a given area. Most often when people think of biodiversity they think of species diversity.
- Genetic diversity measures the amount of inherited genetic variability contained within a populations of species. Even when species are not extinct, their survival can be severely compromised if genes that confer specific survival traits such as disease resistance or environmental tolerance are lost when population size is decreased by habitat fragmentation or other effects.
- Ecosystem diversity describes the variety of communities or habitats that exist. Ecosystem diversity is much harder to measure because the boundaries of many communities or habitats are not usually fixed like that of a pond, but rather they gradually change from one type to another over a transition zone.
How many Species are there?
Estimates of the total number of species vary considerably from 3 million to 30 million, but most estimates put the range between 5 and 10 million (Wilson, 1999). These numbers have changed as new techniques have been developed to more accurately estimate species numbers and as new species are identified. Each year about 13,000 species are discovered and added to the 1.4 million species that have been catalogued so far. The majority of new species are invertebrates, plants, and bacteria, but even large vertebrates are still being discovered. In 1990, a new species of monkey was discovered. It has been estimated from catches examined in Amazon fish markets that as much as 40 percent of South American freshwater fishes are still not identified.
Mathematically the two components of biodiversity are richness and evenness. Richness is a measure of how many organisms exist in a given area. Evenness measures whether each species in a community is represented by about the same number of individuals, or whether one or two species have very large populations and other species have smaller populations. Two communities could be equally diverse in numbers of species but differ greatly in terms of evenness. A variety of mathematical techniques have been developed, but it is often most convenient for a scientist to use an index based on the proportional abundance of species that produces a single number that can represent both richness and abundance. The most widely used of these indices is the Shannon index. Another widely used index is the Simpson's index, which is weighted toward the species with the highest abundances. Both of these indices were developed in the 1940s but gained in popularity when their use was promoted by ecologists Margalef and MacArthur in the 1950s.
Importance of Biodiversity
Species can be considered to have instrumental or inherent value. A species would have instrumental value if it was useful to humans, for example it can be used to create life saving medicines, or it is aesthetically beautiful. A species would have inherent value if it had some worth apart from its usefulness, for example simply because it exists on the planet. It is extremely difficult to attach a monetary amount to inherent values. Historically, examples of the value of biodiversity are anthropocentric instrumental examples of value. Even in most of the world's great religions species were created to be useful for man. In early Christianity, nature and species existed to be transformed and controlled, but the tenets of piety and austerity demanded a certain respect for God's world. Only a few religions like Jainism and animist religions, rate inherent value of species over instrumental.
Inevitably the debate surrounding the preservation of biodiversity hinges not on science but on ethics. The decisions about how much land should be preserved in order to preserve biodiversity are typically based on value rather than function or on ethics. Clearly all decisions are not based on pure economic value. Biodiversity has a great social, ethical, and cultural, value to humans. Examples of this are preserved in our religion, art, and literature. For example, John Muir's great success in garnering public support to preserve large tracts of the American west was due mostly to the aesthetic appreciation that humans have in nature. This appreciation is still apparent today through the public's support of parks and zoos, and nature and conservation organizations.
Used with permission, originally published in the Encyclopedia of World Environmental History (c) Berkshire Publishing Group 2004, and provided here for individual use only and not for redistribution in any form. Medland, Vicki L. (2004). Biodiversity. In Shepard Krech III, J. R. McNeill, and Carolyn Merchant (Eds.), Encyclopedia of World Environmental History, pp. 125–131. Great Barrington, MA: Berkshire Publishing Group.