|M e a s u r i n g B i o D i v e r s i t y
In its literal sense, biodiversity is the diversity of life, and that can mean different things to different people. One of the commonest ways to measure biodiversity is to simply count species. Anyone can do this. For example, you could count the number of plant species growing in a city lot and compare that to the number growing in a forest (to make a fair comparison, you should use the same plot size in each area).
We might compare two different areassuch as our city lot and the forestbut make two lists for each site: native species, and weeds or exotic species. Often weeds, or invading species, in fact do very well when their native environments are disturbed. And as many parts of the U.S. have discovered, sometimes more (as in more deer, and more deer ticks), is not necessarily a good thing! In this way, we find we're making value judgments about species, as if some species were more important than others. Usually we consider native species 'good' and weeds or exotic species 'bad.'
There are yet other ways to measure biodiversity. Some people give special importance to primitive species (living fossils), or to species that have very small geographic ranges (local endemics), and thus are very prone to extinction. Another way to evaluate species is by their ecological roles. For example, keystone species, such as jaguars and elephants, have a major impact on the entire ecosystem, and thus are especially important to protect.
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