Biogeography

“ It seemed to him incredible that the well-defined and practically so important distinctions based on natural vegetation, everywhere recognized and continually acted upon by farmers and settlers, should not be traceable to definite physical and chemical differences in the respective lands, by competent, comprehensively-trained scientific observers, whose field of vision should be broad enough to embrace concurrently the several points of view—geological, physical, chemical and botanical—that must be conjointly considered in forming one’s judgment of land. ”

“ A geological formation is the sum of all the strata deposited over the whole surface of the earth during one of these epochs: a geological fauna or flora is the sum of all the species of animals or plants which occupied the whole surface of the globe, during one of these epochs.
The population of the earth's surface was at first very similar in all parts, and only from the middle of the Tertiary epoch onwards, began to show a distinct distribution in zones. ”

“ The factors of a habitat are water-content, humidity, light, temperature, soil, wind, precipitation, pressure, altitude, exposure, slope, surface (cover) , and animals. To these should be added gravity and polarity, which are practically uniform for all habitats, and may, in consequence, be ignored in this treatise. Length of season, while it plays an important part in vegetation, is clearly a complex and is to be treated under its constituents. Of the factors given, all are regularly found in each habitat, though some are not constantly present. ”

“ From the point where the geological formations approach the present time, plant and animal geography also assists geology in increasing the weight of the reasons for an origin of organisms through descent. With the tertiary period, the fauna and flora of the globe, which in former periods had a nearly uniform character all over the earth and showed no climatic differences, begin to separate according to climate, zones, and greater continents. ”

“ It was remarked that the same species of organic remains cannot be traced horizontally, or in the direction of the planes of stratification for indefinite distances. This might have been expected from analogy; for when we inquire into the present distribution of living beings, we find that the habitable surface of the sea and land may be divided into a considerable number of distinct provinces, each peopled by a peculiar assemblage of animals and plants. In the Principles of Geology, I have endeavoured to point out the extent and probable origin of these separate divisions ”

“ But it will be found that, in order to treat geology in a truly scientific manner, we must bring together all the classes of speculations concerning known causes of change; and the Organic Dynamics of Geology, or of Geography, if the reader prefers the word, appears not an inappropriate phrase for one part of this body of researches.
As has already been said, the species of plants and animals which are found embedded in the strata of the earth, are not only different from those which now live in the same regions, but, for the most part, different from any now existing on the face of the earth. ”

“ The animal ecology of a particular region can only be properly investigated after the habitats and plant formations have been carefully studied. Here, as in floristics, a great deal can be done in the way of listing the fauna, or studying the life habits of its species, without any knowledge of plant ecology; but an adequate study must be based upon a knowledge of the vegetation. Although animal formations are often poorly defined, there can be no doubt of their existence. Frequently they coincide with plant formations, and then have very definite limits. ”

“ On the other hand, ecological plant geography seeks to ascertain the distribution of plant communities, such as associations and formations, and enquires into the nature of the factors of the habitat which are related to the distribution of plants—plant forms, species, and communities. In a general way, floristic plant geography is concerned with species, ecological plant geography with vegetation. The study of the distribution of species dates back to the time of the early systematists, the study of vegetation to the time of the early botanical travellers. ”

“ A society is in entire correspondence with the physical factors of its area, and the same is true of the vegetation of a province. Nevertheless, many societies usually occur in a single habitat, and a province contains many habitats. The final test of a habitat is an efficient difference in one or more of the direct factors, water-content, humidity, and light, by virtue of which the plant covering differs in structure and in species from the areas contiguous to it. ”

“ In consequence, it deals with the subdivisions of zones, arising from physical differences within the symmetrical area. It deals with vegetation areas of every rank below that of major zone, with the habitat and geographical areas of species, and, in a certain way, with the correspondence of vicarious genera. The breaking up of vegetation into formations is a striking example of alternation. The same phenomenon occurs in every formation, producing consocies and minor plant groups, and everywhere giving variation to its surface and structure. ”

“ On purely geographical grounds, also, a large area stimulates differentiation by presenting a greater diversity of natural conditions, each of which tends to produce its appropriate species or variety.295 Consider the different environments found in a vast and varied continent like Eurasia, which extends from the equator far beyond the Arctic Circle, as compared with a small land-mass like Australia, relatively monotonous in its geographic conditions; and observe how much farther evolution has progressed in the one than in the other, in point of animal forms, races and civilization. ”

“ Yet the zoologist and botanist, well acquainted with the geographical distribution of organic beings in other parts of the globe, would have been able, if distinct groups of species had been presented to them from these regions, to recognize those which had been collected from latitudes within, and those which were brought from without the tropics. ”

“ In the other we study fossils in faunal groups, as successive geological faunas, and the geographic diversity in each geological period—i. e., the evolution of geologic faunas and the causes of geographic diversity in each. In a word, we study the laws of distribution of faunas in time geologically and in space geographically, and the causes of these laws in each case. The first is strictly a branch of zoölogy and botany, and we leave it to these specialists. The second alone belongs properly to geology. ”

“ If we have been observant during our several journeys, and have combined and compared the facts we have collected, it will become apparent that the change we have witnessed has been of two distinct kinds. In our own and immediately surrounding districts, particular species appeared and disappeared because the soil, the aspect, or the vegetation, was adapted to them or the reverse. ”

“ Other departments are also drawn upon; there can be no close study of the soil, the structure of mountains and plains, without mineralogy and geology. Meteorology, too, the science which discusses the climatic conditions of countries and the effects of climate upon the organization of plants, animals, and man, is of no mean value in illustrating geography. Nor can one be a great geographer who does not understand the flora of the world. Not that he needs to be familiar with the myriads of plants, but the laws of growth and the characteristics of localization must be known. ”

“ 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. ”

“ Such effects, though attributable mainly to man, are produced in some degree by all other animals.
Besides these general effects, it is the existence of organic forms that has conferred on all the sedimentary rocks their fossiliferous character. The records of the climate of each geological period, of the physical geography, of the vegetable productions, and of the animal forms by which the earth was peopled, consist in the remains of the living beings of these several periods, imbedded in the contemporaneous rock formations. ”

“ Many ecological facts are of real diagnostic value, while others are at least of much interest, and serve to direct attention to the plant as a living thing. The loose use of 14terms denoting abundance, which prevails in lists and manuals, should be replaced by the exact usage which the quadrat method has made possible for vegetation. The designation of habitats could be made much more exact, and the formation, as well as the habitat form or ecad, and the vegetation form or phyad, should be indicated in addition. ”

“ In every one of these beautiful, picturesque, accessible, and very limited districts, you have congregated specimens of the fauna and flora of rivers, groves, forests, and plains, which have no longer a place on the terraqueous globe. Compared with the living or extinct races they constitute a chapter in natural history nowhere else to be seen or studied.
Thus of eight genera of plants in the wealden, there are [203] only four common to it and the oolites, but not a single species. Of the hundreds of zoophytes in the older formation, not one occurs in the newer. ”

“ The specific identity, to any extent, of the flora and fauna of one area with those of another, depends on both areas forming, or having formed, part of the same specific centre, or on their having derived their animal and vegetable population by transmission, through migration, over continuous or closely contiguous land, aided, in the case of alpine floras, by transportation on floating masses of ice. ”

“ The connexion between climate and vegetation has also been studied. Quite recently under the name of “Ecology” or “Oecology” the study of plants in relation to each other and to their environment has become the subject of systematic investigation.
The subject of palaeontological botany (see Palaeobotany) has been advanced by the researches of both botanists and geologists. The nature of the climate at different epochs of the earth’s history has also been determined from the character of the flora. ”

“ One instructive lesson suggested by this hasty glance at the plant life of North America is furnished by the quick response that vegetation gives to conditions of environment. 256 Throughout the greater divisions of the forest, prairies, grass-covered plains and valleys, and flower-decked mountain heights there are constant variations from locality to locality in the plant life to meet seemingly obscure or but slight changes in the conditions of temperature, humidity, exposure to sunlight, soil composition, soil texture, etc. ”

“ In all these questions of former land connection, anthropo-geography follows the lead of bio-geography, whose deductions, based upon the dispersal of countless plant and animal forms, point to the paths of human distribution. ”

“ Proofs of varied Physical Conditions.—Organic remains are either of terrestrial, fresh-water, or marine origin, and they are therefore of the utmost value to the geologist in deciphering the history of those great changes which have culminated in the present. But we can go a step further than this. We know that at the present day the distribution of animal and vegetable life is due to a variety of causes—to climatic and physical conditions. The creatures inhabiting arctic and temperate regions contrast strongly with those that tenant the tropics. ”

“ In certain regions, alike in the tropics and in temperate zones, we find that plants reach their maximum size, combined with great differentiation of structure, and the formation of woody stems which offer great resistance to varying conditions of climate and weather. Such highly-organised plants form forests, which still dominate over a large part of the earth’s surface.
Man’s nearest allies, the anthropoid apes and the monkeys, are for the most part forest animals, and the lowest races of men are still forest dwellers. ”

“ Just as some animals and plants, when they are by any cause placed in a medium offering the largest sum of propitious conditions, attest the excellence of that medium by a more complete development of the individual and of the number of individuals; as there exists a zoölogical geography and a botanical geography, which distinguishes and enumerates for each species the most favored or most favorable regions—there exists also a mineralogical geography, which fixes the cantonment of particular minerals in certain countries. ”

“ Lastly, the terrestrial flora became most diversified and most perfect when the highest orders of animals, the mammalia and birds, were called into existence.
Now in the first place, it may be observed, that many naturalists are guilty of no small inconsistency in endeavoring to connect the phenomena of the earliest vegetation with a nascent condition of organic life, and at the same time to deduce from the numerical predominance of certain forms, the greater heat or uniformity of the ancient climate. ”