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Show 140 CAUSES 01~ STATIONS. (Ch. VIII. river, and in the adjoining dry land, is maintained i or between a continent, with its lakes and rivers, and the ocean. It is well known that many birds migrate, during stormy seaso~s, from the sea-shore into the interior, in search of food; wh1lc Others on the contrary urO'ed by like wants, forsake their inland' haunts and live o' n sut:b) stances rejected by t h e t1' de . The migr~tions of fish into rivers during the spawning season supplies another link of the same kind. Suppose the salmon to be reduced in numbers by some marine foes, as by seals and grampuses, the consequence must ~ften be, that in the course of a few years the otters at the d1stance of several hundred miles inland will be lessened in number from the scarcity of fish. On the other hand, if there be a dearth of food for the young fry of the salmon in rivers and estuaries, so that few return to the sea, the sand-eels and other marine species, which are usually kept down by the salmon, will swarm in greater profusion. . It is unnecessary to accumulate a greater number of illus-trations in order to prove that the stations of different plants and animals depend on a great complication of circumstances,on an immense variety of relations in the state of the animate and inanimate worlds. Every plant requires a certain climate, soil, and other conditions, and often the aid of many animals, in order to maintain its ground. Many animals feed on certain plants, being often restricted to a small number, and sometimes to one only; other members of the animal kingdom feed on plant-eating species, and thus become dependent on the conditions of the stations not only of their prey, but of tb~ plants consumed by them. HavinO' duly reflected on the nature and extent of these t:) d' mutual 1·elations in the different parts of the organic an In· organic worlds, we may next proceed to examine the results which may be anticipated from the fluctuations now continually in progress in the state of the earth's surface, and in the geographical distribution of its living productions. CHAPTER IX. The circumstances which constitute the Stations o£ Animals are changeableExtension of the range of one species alters the condition of others-Supposed clTects which may lhave followed the first entrance of the Polar Bears into Icclaml-The first appearance of n new species in a region causes the chief disturbance-Changes known to have resulted from the advance of human po1mlation-Whether man increases the productive powers of the earth-Indigenous Quadrupeds and Birds of Great Britain known to have been extirpated -Extinction of the Dodo-Rapiu propagation of the domestic Quadrupeds over the American Continent-Power of exterminating species no prerogative of Man-Concluding Remarks. WE have seen that the stations of animals and plants depend not merely on the influence of external agents in the inanimate world, and the relations of that influence to the structure and habits of each species, but also on the state of the contemporary living beings which inhabit the same part of the globe. In other words, the possibility of the existence of a certain species in a given locality, or of its thriving more or less therein, is determined not merely by temperature, humidity, soil, elevation, and other circumstances of the like kind, but also by the existence or non-existence, the abundance or scarcity, of a particular assemblage of other plants and animals in the same region. If we show that both these classes of circumstances, whether relating to the animate or inanimate creation, are perpetually changing, it will follow that species are subject to incessant vicissitudes ; and if the result of these mutations, in the course of ages, be so great as materially to affect the general condition of stations, it will follow that the successive destruction of species must now be part of. the regular and constant order of Nature. It will be desirable, first, to consider the effects which every extension of_ the numb~rs or geographical range of one species |