Biosphere

“ The total amount of biomass is fixed ultimately by those elements that make up the bulk of living matter (such as carbon, hydrogen and oxygen) , and the elements that are micro-nutrients but nonetheless essential to life, such as iron. People are no exception, although in the evolutionary battlefield we have gained a dominant position by developing the technology to exploit the entire biosphere to the extent that, for the time being, we seem able to defy ecological laws.
10.2 RESOURCE CYCLES AND PEOPLE
All species exploit the resources of ecosystems in order to survive. ”

“ If inorganic matter was rapidly collected by the action of violent causes, so under an extraordinary state of things, of climate, moisture, atmosphere, and other physical arrangements, organized bodies, vegetable and animal, would multiply as rapidly. A condition of nature that produced uniformity of vegetation over the entire surface of the globe, as the coal deposit everywhere manifests, and all of gigantic dimensions in every family of plants, is not merely to be denominated tropical, and its results calculated by a scale of existing weights and measures. ”

“ With water, the primarily organic circulation extends from the plant to the soil below and the air above and passes into still more complicated interrelations in animal bodies; and the locus of most effective energizing on the planet is the infinitely complex surface—the soil with its extensions in stem, leaf, flower, fruit and other organic bodies—at which water is continually passing from one form to another, absorbing or yielding latent heat, and mechanically interacting with the sun in seizing and storing and transferring molecular action. ”

“ In view of certain investigations which have been made of water flora and fauna for special purposes, I add a few words on the place of the water flora in the economy of Nature. The lower vegetation is of very great importance, especially the microscopic plants, innumerable plantations of which inhabit extensive tracts of all, and especially of northern, lakes. They move around in the water in masses or singly, changing the deep blue color of the spots destitute of organisms into green or dirty yellow. ”

“ This subject is as much a part of ecology as is forestry. It is intrinsically that subdivision of ecology which deals with the edaphic factors of the habitat, and their relation to the plant. Since the basis is physics, there has been a general tendency to overvalue the determination of soil properties, and to ignore the fact that these are decisive only when considered with reference to the living plant. As the soil contains the water which is the factor of greatest importance to plants, soil physics is an especially important part of ecology. Its methods are discussed under the habitat. ”

“ 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. ”

“ To understand rightly the daily accumulating stores of organic reliquiæ, requires more than a slight knowledge of existing nature,—more even than an acquaintance with animal and vegetable forms. The philosophy of their existence must be considered—the variations of their structure, with respiration in air or in water—life in fresh or salt water—in trees or on the ground—carnivorous or herbivorous food—their geographical distribution dependence—on climate and atmospheric conditions. ”

“ This home economy of plants, or how they meet the environment and each other, is called Plant Ecology, a phase of botany now much studied, for it tells us more directly than most other plant research what the actual response to various factors of the environment may be. Just as plant distribution is the reflection of many, usually widely operating forces, so ecology narrows down to individual plants or groups of them the impact of the immediately surrounding conditions upon vegetation. ”

“ 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. ”

“ All other animals, and all plants as well, are surrounded by and use practically the same things from their environment as we do. The potted plant in the window, the goldfish in the aquarium, your pet dog at home, all use, as we will later prove, the factors of their environment [Pg 20] in the same manner. Air, water, light, a certain amount of heat, soil to live in or on, and food form parts of the surroundings of every living thing.
An experiment that shows the air contains about four fifths nitrogen. ”

“ The action of the forest on the earth is chiefly mechanical, but the organic process of absorption of moisture by its roots affects the quantity of water contained in the vegetable mould and in the mineral strata near the surface, and, consequently, the consistency of the soil. In treating of the effects of trees on the moisture of the atmosphere, I have said that the forest, by interposing a canopy between the sky and the ground, and by covering the surface with a thick mantle of fallen leaves, at once obstructed insulation and prevented the radiation of heat from the earth. ”

“ In such places we are faced with a vegetation exhibiting a great number of species and a marked variety of form, and by no means so easy to correlate with its environment as those which we have been considering. In a wide sense, the nature of the vegetation is largely dependent on the degree of aeration of the water and the amount of dissolved mineral salts which it contains, an increase of either (within limits) resulting in a richer flora. ”

“ 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. ”

“ In zoölogy the environment of an organism means the sum-total of the conditions of life that surround and affect it, such as food, air, water, climate, etc.
We have already stated that as far as evolution is concerned the structures of fundamental importance in an organism are the Germ-Cells; therefore, for our purposes, we will define environment to be the sum-total of the conditions that directly or indirectly influence in any way the germ-cells, by which variations in them may be produced, or through which stability may be maintained. ”

“ But whatever may have been the special features of its scenery, there can be no doubt of the land's existence. The carbonized plants stand up to tell us of its strange and luxuriant vegetation. We have listened to their story, and suffered them to lead us away into forest, and lake, and sea, to look on the various forms of life, vegetable and animal, which abounded in that far-distant age. ”

“ As a forest becomes denser, its layers disappear from the upper downward, the ground layer always being the last to disappear because of its ability to grow in very diffuse light. A vertically zoned formation shows a complex series of reactions. The primary layer determines the amount of heat, light, water, wind, etc., for the subordinate layers in general. Each of these layers then further determines the amount for those below it, the ground layer being subject in some degree to the control of every layer above it. ”

“ In plants, too, there is an analogous process. The - 140 - atmospheric air is by them decomposed, part of it being given off again, and part retained to build up the organic structure. Plants withdraw mineral matter from the soil, animals feed upon plants, and thus the earthy substances, after having formed a part, first of rock masses, then of vegetable, and subsequently of animal organizations, are returned again to the soil, whence to be once more withdrawn and undergo new cycles of mutation. ”

“ 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 place, or of its thriving more or less therein, is determined not merely by temperature, humidity, soil, elevation, and other circumstances of the like kind ”

“ If we add now the transport of organisms, particularly of seeds, insects and birds, and the influence of winds on the migration of higher animals and man himself, through the medium of ocean currents, we shall see how the face of the organic world gathers its lineaments as broadly and depends on the atmosphere as intimately as the contours of a continent. The organic in turn reacts on the purely physical and we recognize at last that, touch the globe where we will in scientific inquiry we pick up some link in an endless chain. ”

“ In answer to this objection, it may, with some plausibility, be urged that a large majority of the species with restricted areas are mountain plants; that there is much reason to believe that most of these peculiar species did originate within insulated areas, at a time when these were separated by the sea from neighbouring masses, where the conditions of life for each organism must have been somewhat different; and that in a few instances local peculiarities of soil, either chemical or mechanical, may [60] explain the fact that a particular species is limited to a very small district. ”

“ The physical symmetry of a habitat depends upon the distribution of water in it, and this is profoundly affected by the soil and the physiography. The influence of precipitation is slight or lacking, as it is nearly uniform throughout the habitat; the effects of wind and humidity are more localized. Differences of soil rarely obtain within a single habitat, though often occurring in a zoned series. The strikingly zonal structure or arrangement of habitats is nearly always due to differences in water-content produced by physiographic factors, slope, exposure, surface, and altitude. ”

“ Modification of habitat. As the final factors in ecesis and competition, water, light, and temperature control the grouping of plants into vegetation. An efficient change in one of these, or in all of them, brings about a visible adjustment in the structure of the plant group concerned. Modifications 308of water-content and light are readily produced in the field by drainage, irrigation, shading, clearing, etc. In fact, all the changes of habitat indicated under experimental evolution serve equally well to initiate experiments in experimental vegetation ”

“ 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. ”

“ The principal causes which enable a certain assemblage of plants thus to maintain their ground against all others depend, as is well known, on the relations between the physiological nature of each species, and the climate, exposure, soil, and other physical conditions of the locality. Some plants live only on rocks, others in meadows, a third class in marshes. Of the latter, some delight in a fresh-water morass,—others in salt marshes, where their roots may copiously absorb saline particles. ”

“ The gaseous emanations, the vehicles of this aroma, appear to be disengaged in proportion as the soil, which contains the remains of an innumerable multitude of reptiles, worms, and insects, begins to be impregnated with water. Wherever we stir the earth, we are struck with the mass of organic substances which in turn are developed and become transformed or decomposed. Nature in these climes seems more active, more prolific, and, so to speak, more prodigal of life. ”

“ 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. ”

“ The fossils of trees and plants, as well as reptiles, that we find in the great coal measures of the world, show that they were of large tropical growth, and this is shown not only in the temperate zone, but in the zone farther north. For ages and ages this rank growth of vegetation grew up and fell down until a great layer of vegetable matter was formed, which at a later time was covered over by other stratifications of earth material, so that these great layers of vegetable formation were hermetically sealed and pressed down by an enormous weight that increased as time went on. ”