biodiversity 

Another one of those words everybody loves but nobody can define. How much biodiversity is needed? If there are a 10 million species and we lost half, we would still have 5 million. That is still staggeringly diverse. 

"Distribution of species across the Earth shows strong latitudinal and altitudinal gradients with the number of species decreasing with declining temperatures." Is that a problem? 

* * *

To date, no unequivocal link has been established between the
measured exposure (i.e., the concentration of toxicants in the
environment) and quantitative measures of regional biodiversity
(i.e., the regional taxonomic richness pool). Hence, although
chemical contaminants are well known as an important
driver for biodiversity loss (1, 10–28), there is scarce empirical evidence
to support such opinion for the large-scale taxonomic pools.

This problem holds true even for agricultural pesticides, which
are among the best ecotoxicologically characterized and regulated
groups of contaminants. Essentially, it remains unknown
whether, to what degree, and at what concentrations pesticides
cause the species losses at the regional scale.

Source:

Pesticides reduce regional biodiversity of stream invertebrates
Mikhail A. Beketova,1, Ben J. Keffordb, Ralf B. Schäferc, and Matthias Liessa
Edited by David Pimentel, Cornell University, Ithaca, NY,
accepted by the PNAS Editorial Board May 13, 2013

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