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Biodiversity: Nature's Insurance Policy Against Catastrophe
From: Woods Hole Oceanographic Institution
| By:
Vicky Cullen |
EDITOR'S INTRODUCTION |
Human existence is heavily dependent on the products of plants and animals--everything from wood and food to medicines. With estimates of up to 10,000 different terrestrial organisms becoming extinct each year, and much of that destruction resulting from human activities, there is a pressing need to learn more about the wide variety of organisms that inhabit the Earth and to raise awareness of the importance of biological diversity.
In this feature, Vicky Cullen of the Woods Hole Oceanographic Institution explores the concept of biological diversity, or biodiversity, and its importance to the everyday activities of all species. |
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| Cyclothone. | |
 ost of us don't give a second thought to squashing a mosquito, especially one that has just bitten us, and we may say the world would be better off without the pesky things. But would it? Is all of life on Earth a web of life? Is each part diminished a bit when one part weakens or disappears? Does the blue whale, largest of all animals, depend in some way on the smallest marine microbe? |
The term "biodiversity" refers to our planet's wide variety of life forms--Earth's plants, animals and microorganisms, the genes they contain, and the ecosystems they form. Biodiversity is considered at three levels: species diversity, genetic diversity and ecosystem diversity. |
Species diversity. This encompasses the number, types and distribution of species within an ecosystem. More than 1.5 million species of animals and plants have been described by scientists, and only 15 percent are marine. Estimates of the total number of Earth species, a large proportion of them awaiting description, range from 5 million to 100 million. The variation in these estimates depends to some extent on the definition of "species," and there appears to be no definition that fits all branches of science, from population biology through philosophy. By classic definition, a species is something that is seen or perceived to be distinctive, usually morphologically, so organisms with similar distinctions constitute species. The definition most accepted by today's biologists requires reproductive isolation--basically, if two organisms can interbreed and produce fertile offspring, they are usually of the same species, though there are exceptions. |
Genetic diversity. Variation in genes enables organisms to evolve and adapt to new conditions. Selection shapes the pool of genetic variation in an interbreeding population, leads to preference for certain genetic attributes, and results in changes to the frequency of genes within the pool. Large differences in the amount and distribution of genetic variation are due in part to the enormous variety and complexity of habitats, and the different ways organisms make their livings. |
Ecosystem diversity. This refers to the variety of habitats and communities of different species that interact in a complex web of interdependent relationships. It is a dynamic diversity of fluid "boundaries" between both ecosystems and communities or associations. |
While a lot is known about these components of biodiversity, there's also a great deal that is unknown--and we know more about the land than about the sea. For example, a widely quoted book that tracks diversity around the world, the World Resource Institute's Realms, Biomes and Biogeographical Provinces of the World (1986) doesn't even discuss the ocean. |
The value and importance of biodiversity
Sheer diversity itself may be of inestimable value as a foundation for a healthy planet and human well-being. Many ecologists now believe that richly diverse ecosystems are more resilient and better able to recover from such stresses as drought or human-induced habitat destruction than less diverse systems. Some describe biodiversity as nature's insurance policy against catastrophe. Greater diversity offers a range of pathways for primary production and ecological processes such as nutrient recycling; if one pathway is damaged or destroyed, alternatives are available to allow the ecosystem to continue functioning at its usual level. |
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| Microalgae. | |
Diminished diversity puts the functioning of ecosystems at risk. The California Academy of Sciences, which operates a Biodiversity Resource Center, estimates that more than 10,000 species of terrestrial organisms become extinct each year, and the rate of extinction is increasing. The central cause of species extinction is human destruction of natural habitats. |
Of all the benefits we derive from biological resources, ranging from medicine to wood products to recreational settings, food is perhaps the most important. According to the Australian Biodiversity Series, Paper No. 1, "Human existence (and that of most other organisms) is heavily dependent on what biologists call primary producers, mainly plants. Five thousand plant species have been used as food by humans, but less than twenty now feed the majority of the world's population and just three or four carbohydrate crops are staples for a vast majority. One of the important benefits of conservation of biodiversity is the wild plant gene pool that is available to augment the narrow genetic base of these established food crops, providing disease resistance, improved productivity and different environmental tolerances." |
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| Dolphin. | |
Human activities that profoundly affect biodiversity, such as coastal development, logging and transport of species from one habitat to another in ships' ballast tanks, are unlikely to stop. But we can think about what we do, and we can make some choices. We can learn more about the web and its interconnectedness in order to make wise choices. Earth would be a lonely place for Homo sapiens without a bird call, the hope of seeing a fish jump, just knowing that elephants and tigers still roam free--or a mosquito's occasional nip. |
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