Diversity

- Biodiversity

Squirrel or Sciurus carolinensis
Sciurus carolinensis

About 2 million species have been named. Perhaps 50 million remain to be discovered. To understand the impact we humans have on biodiversity, we have to at least estimate the number of species there are and how those numbers are changing. What is a species? Species were first defined in terms of their appearance. The first criterion for including an organism in a species should be that it looks similar to other members of the species.

We have come to use further criteria as we try to make our classification more "natural": Members of a species should: be able to interbreed, be physiologically similar and, occupy similar habitats.

How many species are there? (from NOVA, new page)

Organism	Number Described	Estimated number to be Discovered
Viruses	5,000	about 500,000
Bacteria	4,000	400,000-300 million
Fungi	70,000	1-1.5 million
Protozoans	40,000	100,000-200,000
Algae	40,000	200,000-10 million
Flowering plants	250,000	300,000-500,000
Roundworms	15,000	500,000-1 million
Mollusks	70,000	200,000
Crustaceans	40,000	150,000
Spiders and mites	75,000	750,000-10 million
Insects	950,000	8-100 million
Vertebrates	45,000	50,000

Taxonomy is the branch of biology that names and classifies organisms. Taxonomy is useful because if you know something about a group or category, you can infer something about an unfamiliar organism that is a member of the group. Conversely, if you know something about a member or two of a group, you can make some good guesses about the group as a whole.

Circumscription -- How do you define the categories? How do you set up a category so that it includes only what you want it to? Look at the following example in which a new condition is added at each step:

Circumscription of taxa

People = everybody in the world (~ 6 billion of us).
Who live in the US = Americans (~255 million)
Who live in Kentucky = Kentuckians (~4 million)
Who go to WKU = WKU students (~16 K)
Who take BIO 113 (~ 450, )
Who take BIO 113 with Wyatt (~140 a very exclusive category indeed)

Each category becomes less inclusive (contains fewer people or things). People grouped together in the less inclusive categories can share more characteristics than those grouped in the more inclusive categories. Each category has its own basis (or circumscription) for being a category, and each (regardless of rank) is called a taxon (pl., taxa). Currently, there are (at least) seven heirarcheal levels of taxa used to classify organisms. They are (from the most inclusive to the least inclusive):

The scientific name of an organism is composed of the genus and species names. Present-day humans, for example have the scientific name Homo sapiens; the housecat, Felis domesticus; the red oak tree, Quercas rubra. The scientific name is italicized or underlined and the genus name is capitalized. (mouse over terms to see)

Monera Protoctista Fungi Plants Animals