In some cases it can be shown that widely-different checks act on
the same species in different districts. When we look at the plants and
bushes clothing an entangled bank, we are tempted to attribute their
proportional numbers and kinds to what we call chance. But how false a
view is this! Every one has heard that when an American forest is cut
down, a very different vegetation springs up; but it has been observed that
ancient Indian ruins in the Southern United States, which must formerly
have been cleared of trees, now display the same beautiful diversity and
proportion of kinds as in the surrounding virgin forests. What a struggle
must have gone on during long centuries between the several kinds of trees,
each annually scattering its seeds by the thousand; what war between insect
and insect--between insects, snails, and other animals with birds and
beasts of prey--all striving to increase, all feeding on each other, or on
the trees, 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 fall to the ground according to definite laws;
but how simple is the problem where each shall fall compared to that of 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!
The dependency of one organic being on another, as of a parasite on its
prey, lies generally between beings remote in the scale of nature.
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