How many species are there?
"How many species are there" is a question receiving more attention from biologists and reasons for this are suggested. Different methods of answering this question are examined and include: counting all species; extrapolations from known faunas and regions; extrapolations from samples; methods using ecological models; censusing taxonomists' views. Most of these methods indicate that global totals of 5 to 15 million species are reasonable. The implications of much higher estimates of 30 million species or more are examined, particularly the question of where these millions of species might be found.
Nigel E.Stork
Here is a article from the NYTimes entitled "How Many Species? A Study Says 8.7 Million, but It's Tricky