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Show CHAPTER II THE STRUGGLE FOR EXISTENCE Its importance-The struggle among plants-Among animals-Illustrati,·e ca ·es-Succession of trees in forests of Denmark - The struggle for existence on the Pampas-Increase of organisms in a geometrical ratio-Examples of great powers of increase of animals-Rapid increase and wide spread of plants-Great fertility not essential to rapid increase-Struggle between closely allied species most severeTho ethical aspect of the struggle for existence. THJ£RE is perhaps no phenomenon of nature that is at once so important, so universal, and so little understood, as the struggle for existence continually going on among all organised beings. To most persons nature appears calm, orderly, and peaceful. They see the birds singing in the trees, the insects hovering over the flowers, the squirrel climbing among the tree-tops, and all living things in the possession of health and vigour, and in the enjoyment of a sunny existence. But they do not see, and hardly ever think of, the means by which tkis beauty and harmony and enjoyment is brought about. They do not see the constant and daily search after food, the failure to obtain which means weakness or death; the con stant effort to escape enemies; the ever-recurring struggl ' against the forces of nature. This daily and hourly struggle, this incessant warfare, is nevertheless the very means by which much of the beauty and harmony and enjoyment in nature is produced, and also affords one of the most important elements in bringing about the origin of species. We must, therefore, devote some time to the consideration of its various aspects and of the many curious phenomena to which it gives rise. It is a matter of common observation that if weeds are allowed to grow unchecked in a garden they will soon destroy CHAP. II THE STRUGGLE FOR EXI TENCE 15 a number of the flowers. It is not so commonly known that if a garden is left to become altogether wild, the weeds that first take posse. sion of it, often covering the whole surface of the ground with two or three different kinds, will themselves be supplanted by others, so that in a few years many of the original flowers and of the earliest weed · may alike have disappeared. This is one of the very simplest cases of the struggle for existen ce, r esulting in the succc ·si vc cli.-placcmcnt of one set of species by another ; but the exact canHes of this di splacement are by no mean · of such a simple nat nrc. All the plants concerned may he perfectly ha-rdy, all may grow freely from seed, yet when left a-lone for a number of years, each set is in turn driven out by a succeeding set, till at the end of a considerable period - a century or a few centuries perhaps-hardly on e of the plan ts which fi rst monopolised the ground would be found there. Another phenomenon of an analogous kind is presented by the different behaviour of introduced wild plants or animals into countries apparently qui te as well suited to them as those which they naturally inhabit. Agassiz, in his work on Lake Superior, states that the road ·ide weeds of the northeastern United States, to the number of 130 species, arc all European, the native weeds having disappeared westward s ; and in New Zealand there are uo lc s than 250 species of naturalised European plant, more th<tn 100 specie of which have spread widely over the coun t ry, often displacing the native vegetation. On the other hand, of the many hundreds of hardy plants whi ch produce seed fr eely in our gardens, very few ever run wild, and hardly any have become common. Even attempts to naturalise suitable plants usually fail ; for A. de Candolle states that several botanists of Paris, Geneva, and especially of Montpellier, have sown the seeds of many hundreds of species of hardy exotic plants in what appeared to be the most favourabl e situations, but that, in hardly a single case, has any one of them become naturalised.1 Even a plant like the potato-so widely cultivated, so hardy, and so well adapted to spread hy means of its many-eyed tubers-has not established itself in a wild state in any part of Europe. It would be thought that Australian plants would easily rnn 1 Geogrctphie Botaniq11e, p. 798. |