between insect and insect--between insects, snails, and other animals, with
birds and beasts of prey--all striving to increase, and all feeding on each
other or on the trees, or their seeds and seedlings, or on the other plants
which first clothed the ground and thus checked the growth of the trees!
Throw up a handful of feathers, and all must fall to the ground according
to definite laws; but how simple is this problem compared to the action and
reaction of the innumerable plants and animals which have determined, in the
course of centuries, the proportional numbers and kinds of trees now
growing on the old Indian ruins!"--(pp. 74, 75.)


For reasons obvious upon reflection, the competition is often, if not
generally, most severe between nearly related species when they are in
contact, so that one drives the other before it, as the Hanoverian the old
English rat, the small Asiatic cockroach in Russia, its greater congener,
etc. And this, when duly considered, explains many curious results; such,
for instance, as the considerable number of different genera of plants and
animals which are generally found to inhabit any limited area.


"The truth of the principle that the greatest amount of life can be
supported by great diversification of structure is seen under many natural
circumstances. In an extremely small area, especially if freely open to
immigration, and where the contest between individual and individual must
be severe, we always find great diversity in its inhabitants. For instance,
I found that a piece of turf, three feet by four in size, which had been
exposed for many years to exactly the same conditions, supported twenty
species of plants, and these belonged to eighteen genera, and to eight
orders, which showed how much these plants differed from each other. So it
is with the plants and insects on small and uniform islets; and so in small