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Page:Popular Science Monthly Volume 83.djvu/173

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By the late WALTER L. HAHN, Ph.D.

THAT the animal life of North America is changing is a statement requiring no proof. Every one knows that deer, elk, moose, wolves, bison and many other animals are no longer found in places where they were once numerous. Nearly every one also knows that some pests, such as rats and mice and several noxious insects, have been brought to this country from Europe, while the potato beetle and some other species, natives of North America, have multiplied and extended their range.

It is impossible, within the limits of this paper, to specify all the changes that have taken place and are now in progress. Hence it will be my aim to point out certain general tendencies, and certain general influences at work upon our fauna, the word fauna being a somewhat technical term used to designate the sum total of the animal life, great and small, in any circumscribed region.

If asked why the great game animals have disappeared from certain regions, most people would doubtless say, "Indiscriminate slaughter has exterminated them." This answer is undoubtedly correct as far as it goes. For a full explanation of all of the changes that have taken place in our fauna we must seek deeper reasons. Why has not "indiscriminate slaughter" exterminated the mice and rats and other noxious creatures against which we have waged ceaseless war for many generations? In other words, what are the biological and physical conditions that determine whether an animal species shall survive or perish in modern America?

A living organism, even the simplest, is a thing of vastly greater complexity than any mere chemical compound or any physical law. We know how to kill individual organisms, but frequently we do not know what will exterminate a species. If a lion and a lamb lie down together, we know which will be on the inside. But if a given number of lions and a given number of lambs inhabit a great area we can not predict the exact results; and this illustrates the futility of trying to make a definite analysis of the future of any particular species.

I shall now consider the future of North American animals from the general standpoints of size, habitat, relation to man, fecundity, mental traits, and finally give a few interesting facts not comprehended in the above classification.