TRICKLE DOWN POISON
century will see the end of significant evolution of large plants
and terrestrial vertebrates in the tropics," [Michael Soulé
wrote in his chapter in Conservation Biology]. The end of evolution?
Yes - although what he meant, more precisely, was the end of speciation.
Existing species of trees and of vertebrate animals might continue
to evolve incrementally within a single lineage, but they would no
longer split into new and distinct lineages. This is a damned serious
claim, since such splitting constitutes one of the main sources of
biological diversity. Soulé's logic was based on the worldwide
attrition of wild landscape as well as on the biogeography and genetics
of speciation. Because of habitat destruction and fragmentation throughout
the tropics, he argued, and because the nature reserves that humanity
grudgingly sets aside will be too small, we should expect a time in
the near future when vertebrate and tree speciation virtually stop.
Each species will have barely enough habitat (at best) to maintain
itself as a viable population, but not enough to allow it to split
into several divergent populations. Each reserve will offer inadequate
area, inadequate topographic relief, inadequate pockets of geographical
isolation, to foster allopatric speciation among large creatures.
As species are lost to extinction, the losses won't be counterbalanced
by new species, and Earth will grow gradually impoverished of large-bodied
animals and plants. The invertebrate animals and simpler plants-those
creatures that are generally much smaller and more numerous-may not
be so sorely affected. But for the overall diversity of large vertebrates
and trees, if Soulé is correct, the consequences will be sever.
Species of rare ape will disappear, and no new ape species will arise.
Species of feline will go extinct, and no new felines will evolve.
Species of dipterorcarps, the great hardwoods of Asian rainforest,
will be lost and not gained. The world will be an emptier, lonelier
place. Still, we humans can look forward to sharing the future with
a fair number of beetles, tapeworms, fungi, tarweeds, mollusks, and
mites. Dandelions and silverfish are also a good bet."
-- David Quammen, The Song of the Dodo: Island Biogeography in
an Age of Extinctions, © 1997 Touchstone, NY, NY pp. 528-529.