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Elizabeth Blackwell
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Discovery Channel
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Noted environmentalist Edward O. Wilson describes species richness as the size of a population and the manner in which it spreads across the terrain [source: Wilson]. Counting how many plants and animals live in a certain river, for example, and then counting each individual member of that species, is one of the best and most commonly-used methods of assessing that river’s biodiversity.
However, tallying up individual species is no easy task. Scientists generally agree that more than 10 million species exist on Earth (and some think the number is closer to 100 million) [source: Spicer; Eldredge]. Only a fraction of them have been identified and categorized. Counting animals or birds is relatively straightforward, but making note of every miniscule insect and water-borne microbe is a far more daunting task. As such, complete census of a region’s biodiversity at every level may be impossible.
Species richness also depends on the particular area where it is being studied. The Swiss Alps, with their harsh weather and rocky landscape, do not support a wide variety of life forms; the plants and insects that live there have been bred through the centuries to be particularly hardy. The tropical climate of Madagascar, by contrast, supports an enormous variety of plant and animal life, and its isolation has allowed many species to develop in ways found nowhere else in the world. The thriving wildlife of Madagascar makes an alpine meadow look positively barren in comparison -- but as long as the Alps support their native life forms, they can still be considered species-rich.
Unfortunately, species richness is in decline across the globe. Species have always gone extinct throughout the Earth’s history, but human activity has clearly accelerated the process. Species are now vanishing 100 times faster than they did before the arrival of humans [source: Wilson]. By some estimates, we are losing 30,000 species each year [source: Eldredge]. Given the interdependence of life on Earth, each loss affects the whole in its own way, and each decrease in species richness increases the likelihood of further environmental damage to come.
Sources:
Eldredge, Niles. Life in the Balance: Humanity and the Biodiversity Crisis. Princeton University Press. 1998.
Novacek, Michael (ed.). The Biodiversity Crisis. The New Press. 2001.
Spicer, John. Biodiversity. Oneworld Publications. 2006.
Wilson, Edward O. The Diversity of Life. Harvard University Press. 1992. -
Species richness, which refersto how many species exist in a given area, is an important measure of biodiversity, but it's by no means the only measure. Another way to think about biodiversity is to consider the diversity existing in other taxonomic classifications above the species level. These taxonomic classifications include genera, families, orders, classes and phyla.
To understand this distinction, think about insects -- the largest class of arthropods. A huge number of insect species, in many orders and families, live on land. You might think this makes insects more important when it comes to biodiversity. But in marine environments, there are far more phyla than there are in terrestrial environments. In fact, several animal phyla exist only in ocean habitats. This kind of diversity could be considered more valuable than biodiversity based on species richness alone.
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