>
> >Bee-population declines are linked to nutritional shortages caused by
> land-use intensification, which reduces diversity


The key word is "diversity."

Allow me to return to Charlie's point that there is still a large biomass
of species in ag lands.  It is not the biomass that is as important as is
the diversity, since ecosystems with greater diversity tend to be more
stable.

In the corn ecosystem, a single species of herbivore (e.g., corn rootworm)
can wreak havoc and collapse the entire system.

In the diverse community prior to tillage and planting in corn, there were
numerous species of forbes, grasses, and perhaps shrubs and trees.  As well
as a layer of decomposing plant matter on the soil surface, and deep
penetration of the soil by the roots of some species.  Each plant species
provided species-specific food and habitat niches for a wide diversity of
specialized herbivores, predators, and decomposers.

When that complex and diverse system is replaced with a weed-free
monoculture, all those niches disappear, and along with them any species
dependent upon the existence of those niches.

On the other hand, the few species that are able to exploit the narrower
diversity of niches can thrive, as Charlie pointed out.  But it is only the
few.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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