Biogeographic region

“ In the first place, it is clear that when any region is stocked with as great a variety of animals and plants as the productive powers of that region will enable it to support, the addition of any new species, or the permanent numerical increase of one previously established, must always be attended either by the local extermination or the numerical decrease of some other species. ”

“ The physical causes of zonation are by far the most important. They arise from differences in temperature, water, and light. In the large, temperature differences are the most important, producing the great zones of vegetation. In a particular region or habitat, variations of water-content and humidity are controlling, while light, as shown above, is important in the reactions of forest and thicket. Physical factors produce zonation in a habitat or a series of habitats, when there is either a gradual and cumulative, or an abrupt change in their intensity. ”

“ It is obviously impossible that successions in desert lands, in polar barrens, or upon alpine stretches should terminate in forest stages. In these, grassland must be the ultimate condition, except in those extreme habitats, alpine and polar, where mosses and lichens represent the highest type of existing vegetation. Forests are ultimate for all successions in habitats belonging to a region generally wooded, while grassland represents the terminus of prairie and plains successions as well as of many arctic-alpine ones. ”

“ But in looking at the vegetation of regions through which one travels it must never be forgotten that its general type, such as forest, or grassland, or desert, or what not, is the result of usually widely operating climatic forces, while many, often quite extensive, plant societies in the region are the result of the local environment. There is often an active struggle as to the dominance of the type dictated by the climate of the place, and the local conditions of soil that tend to nullify general response to it. ”

“ Certain it is that each separate region both of land and water, from the frozen shores of the polar circles to the burning regions of the torrid zone, possesses a flora peculiarly its own. The whole globe has been divided by physical geographers into various botanical districts, differing almost entirely in their specific vegetable productions, the limits of which are most decided when they are separated by a wide expanse of ocean, mountain chains, sandy deserts, salt plains, or internal seas. ”

“ Each region is studied by itself, but reference will often have to be made to all the other regions; and wherever we begin, we must occasionally refer to facts which will be given further on. As, however, the great northern continents form the central mass from which the southern regions, as it were, diverge, and as the Palæarctic region is both more extensive and much better known than any other, it undoubtedly forms the most convenient starting-point for our proposed survey of the zoological history of the earth. ”

“ One will surpass all others in the possession of peculiar families; another will have many characteristic genera; while a third will be mainly distinguished by negative characters. There will also be found many intermediate districts, which possess some of the characteristics of two well-marked regions, with a few special features of their own, or perhaps with none; and it will be a difficult question to decide in all cases which region should possess this doubtful territory, or whether it should be formed into a primary region itself. ”

“ That entire sea may be considered as one zoological province; for although certain species of testacea and zoophytes may be very local, and each region has probably some species peculiar to it, still a considerable number are common to the whole Mediterranean. If, therefore, at some future period, the bed of this inland sea should be converted into land, the geologist might be enabled, by reference to organic remains, to prove the contemporaneous origin of various mineral masses scattered over a space equal in area to half of Europe. ”

“ The vegetation of Australia, another region similarly placed in respect of clime, is even more peculiar. These facts are the more remarkable when we discover that, in most instances, the plants of one region have thriven when transplanted to another of parallel clime. This would shew that parity of conditions does not lead to a parity of productions so exact as to include identity of species, or even genera. Besides the various isolated regions here enumerated, there are some others indicated by naturalists as exhibiting a vegetation equally peculiar. ”

“ The sub-divisions of the Nearctic region, although pretty clearly indicated by physical features and peculiarities of climate and vegetation, are by no means so strongly marked out in their zoology as we might expect. The same genera, as a rule, extend over the whole region; while the species of the several sub-regions are in most cases different. Even the vast range of the Rocky Mountains has not been an effectual barrier against this wide dispersal of the same forms of life ”

“ It has been stated, that species are in general local, some being confined to extremely small spots, and depending for their existence on a combination of causes, which, if they are to be met with elsewhere, occur only in some very remote region. Hence it must happen that, when the nature of these localities is changed, the species will perish; for it will rarely happen that the cause which alters the character of the district will afford new facilities to the species to establish itself elsewhere. ”

“ The phenomena of variation as influenced by locality have not hitherto received much attention. Botanists, it is true, are acquainted with the influences of climate, altitude, and other physical conditions in modifying the forms and external characteristics of plants; but I am not aware that any peculiar influence has been traced to locality, independent of climate. Almost the only case I can find recorded is mentioned in that repertory of natural-history facts, ‘The Origin of Species,’ viz. that herbaceous groups have a tendency to become arboreal in islands. ”

“ So vast is the region occupied by the Pacific forest and so varied the conditions dependent upon climate, soil, and elevation which influence its growth, that great variations in the genera and species of trees composing it are to be expected. ”

“ In mammalia, reptiles, and insects, it is even more difficult to maintain such divisions, so that on the whole it seems better to treat the entire area as one sub-region, although recognizing the fact of its zoological and geographical diversity, as well as its vast superiority over every other sub-region in the number and variety of its animal forms. ”

“ The Neotropical region is very rich in peculiar genera, though but moderately so in number of species. The Oriental {332}region closely approaches it in both respects; but the Australian region is by far the richest, possessing nearly double the genera and species of any other region, and abounding in remarkable forms quite unlike those of any other part of the globe. ”

“ Of the species belonging to the Mediterranean region, which constitute more than one-half of the vegetation of the middle zone, and about one-third of that of the higher zone of the Atlas, the large majority are widely diffused species. The remaining number, for the most part mountain plants, may be divided into three nearly equal sections, some being common both to Southern Spain and Algeria, others to the Atlas and Southern Spain exclusively, and others to the Great Atlas and the Lesser Atlas of Algeria. ”

“ Variation and natural selection would also afford a key to a multitude of geological facts otherwise wholly unaccounted for, as, for example, why there is generally an intimate connection between the living animals and plants of each great division of the globe and the extinct fauna and flora of the post-tertiary or tertiary formations of the same region; ”

“ Broadly speaking, the American portion of the sub-region consists of an Atlantic and Pacific forest area and an intervening non-forest one, partly occupied by the Rocky Mountains, partly by intervening plains. Its arboreal vegetation is richer both in genera and species than that corresponding to it in the Old World. ”

“ The maritime plain and open river valleys of northern France show a complete fusion of the native Celts with the Saxons, Franks, and Normans who have successively drifted into the region, just as the Teutonic and scanter Slav elements have blended in the Baltic plains from the Elbe to the Vistula.
Change of habitat.
Here are four different classes of geographic influences, all which may become active in modifying a people when it changes its habitat. Many of the characteristics acquired in the old home still live on, or at best yield slowly to the new environment. ”

“ This coincides better than any other geographical line with the natural division between the cooler-temperate and the warm-temperate vegetation of the Atlantic States. The rapid increase of population west of the Mississippi River, and the growing need of a Manual covering the flora of that section, have seemed a sufficient reason for the extension of the limits of the work westward to the 100th meridian, thus connecting with the Manual of the Flora of the Rocky Mountain Region by Prof. ”

“ They were moving above this chaotic region as if carried along by the breath of a tempest, seeing the summits fly under their feet, looking down the cavities, climbing the ramparts, sounding the mysterious holes. But there was no trace of vegetation, no appearance of cities, nothing but stratifications, lava streams, polished like immense mirrors, which reflect the solar rays with unbearable brilliancy. There was no appearance of a living world, everything of a dead one, where the avalanches rolling from the summit of the mountains rushed noiselessly. ”

“ It is well known, that this correspondence is recognised in the general facies of the flora and fauna, dependent on generic correspondences, specific representations, and, in some cases, specific identities. But when announcing and illustrating the law that climatal zones of animal and vegetable life are mutually repeated or represented by elevation and latitude, naturalists have not hitherto sufficiently (if at all) distinguished between the evidence of that law, as exhibited by representative species and by identical. ”

“ In some parts of the globe, at the present period, the line of demarcation between distinct provinces of animals and plants is not very strongly marked, especially where the change is determined by temperature, as in seas extending from the temperate to the tropical zone, or from the temperate to the arctic regions. ”

“ The abundance of animal life in the littoral zone and its respective sub-divisions must not be judged of from the number of species named in this table—my object at present being not to give lists of their flora and fauna, but to show how well marked, by characteristic forms, such zones are. ”

“ If the view I have put forward respecting the origin of the flora of the British mountains be true—and every geological and botanical probability, so far as that area is concerned, favours it—then must we endeavour to find some more plausible cause than any yet shown, for the presence of numerous species of plants, and of some animals, on the higher parts of alpine ranges in Europe and Asia, specifically identical with animals and plants indigenous in regions very far north, and not found in the intermediate lowlands. ”

“ Zoogeography and plant geography are concerned with the division of the earth’s surface into regions possessing individual characteristics in regard to their fauna or flora. The principle of regional division, indeed, has become a leading principle of geographical research, in regard not only to fauna and flora, but to man as well ”

“ These divide the Biosphere into regions of distinct and characteristic combinations of plants and animals across a gradation of climates. They tend to be divided by oceans, deserts and massive mountain ranges. ”

“ It will be there seen that each local change in climate and physical geography is attended with the immediate increase of certain species, and the limitation of the range of others. A revolution thus effected is rarely, if ever, confined to a limited space, or to one geographical province of animals or plants, but affects several other surrounding and contiguous provinces. ”

“ Nevertheless most of the evergreen forests of the north must always remain the home of wild animals and trappers, a backward region in which it is easy for a great fur company to maintain a practical monopoly. ”

“ One of the subjects treated of by Physical Geography is the present geographical distribution of plants and animals. The land-surface of the globe has been mapped out into so many biological regions, each of which is characterised by its special fauna and flora. The greatest changes in the flora and fauna of a continent are met with as we pass from south to north, or vice versa. Proceeding in the direction of the latitude, the changes encountered are much less striking. ”

“ Instead of the enormous northern area, in which highly organised and dominant groups of plants have been developed gifted with great colonising and aggressive powers, we have in the south three comparatively small and detached areas, in which rich floras have been developed with SPECIAL adaptations to soil, climate, and organic environment, but comparatively impotent and inferior beyond their own domain. ”

“ Why distinct provinces not more blended.—Perhaps it may be objected to some parts of the foregoing train of reasoning, that during the lapse of past ages, especially during many partial revolutions of the globe of comparatively modern date, different zoological and botanical provinces ought to have become more confounded and blended together—that the distribution of species approaches too nearly to what might have been expected, if animals and plants had been introduced into the globe when its physical geography had already assumed the features which it now wears ”