In this book we have discussed how life is chemistry, but that chemical life evolved over time, and this evolution occurred within an ecological context. One cannot understand the present distribution of flora and fauna without understanding the nature of world ecology. The evolution of complicated life forms took place within a complicated system of interactions, where plants and animals interact and naturally select each other for survival.

The ecological framework will be used to explain the development of the many sources of divisions among human beings, including race, religion, and ethnicity.



As mentioned earlier, to a depth of about sixty kilometers the earth's surface is divided into about a dozen major plates that fit together like the pieces of a jigsaw puzzle. The analysis of the interactions of moving plates provides the basis for understanding most of the Earth's large-scale geological activity. World ecology could not really be discussed before now because the continents did not drift into their present locations until less than 100 million years ago. And even after that time considerable climate changes, such as the ice ages, occurred.

Given the present positioning of the earth's continents, we can talk about the various ecological areas. Biomes are general groupings of similar plant and animal communities based upon the distinctive life forms of the important species in each community. There are many sub-biomes that can be discussed but these are too numerous to be covered here.

Determinants of Biomes

There are many determinants of biomes. The most important ones can be summarized with reference to the climate. The reason why climate is so important is that it largely determines what types of plants, and thus animals, can be supported in a given area. There are many determinants of a region's climate. Two of the major factors are temperature and moisture. Other factors include location in the continental land mass and wind and ocean currents.

The major determinant of temperature is solar radiation. The earth's circular shape means that the sun's rays strike more directly on some parts of the earth's surface than on others. For instance, more sun strikes the equatorial region than any other area. As everyone knows, the equator is located at zero degrees latitude. As movement is made towards either of the earth's poles, the temperature starts to decrease. The resulting temperature regions are: tropical (24 degrees plus Centigrade); sub-tropical (12 - 23.99); temperate (6 - 11.99); boreal (3 - 5.99); sub-polar (1.5 - 3.99); and polar (1.49 degrees and less).

Moisture patterns follow the temperature patterns to a rough degree. In general, the highest levels of moisture prevail at the equator and decline until they hit low points at the deserts which congregate around the tropics of Cancer and Capricorn. From here the moisture levels tend to increase, until one reaches the boreal forests where the moisture levels decline again.

Vegetation patterns reinforce differences in rainfall. It is no accident that the tropical rain forests are located around the equator. The presence of greater warmth and sunlight makes for a plethora of plants, and the plants in turn help create more rain.

Of course, there are many variations in the temperature-moisture patterns, because of regional differences in location vis--vis the continents. If there were no wind and ocean currents, one would expect the coastal areas to be warmer (because they are closer to the warmer ocean) and the interior regions to be colder.

Ocean currents greatly influence ecosystems, especially in coastal regions. For example, the Gulf Stream brings milder temperatures and more moisture to Great Britain and Norway than would normally occur at their latitudes. Another example is that of the cold California Current that is responsible for the mild, wet climate of the northwestern Pacific coast of North America. These areas hold tall dense coniferous rain forests.

Another important climactic factor is the existence of mountainous areas. Mountains affect local climates by blocking the effects of wind and ocean currents, thereby blocking rainfall to continental interiors. Such is the case of the deserts of the western United States, wherein the Sierra Nevadas deny a great deal of moisture to the regions east of the mountain chain.

Major Biomes of the World

The tropical rain forest is very hot and very wet. The major differences between tropical rain forests are due to the amounts of moisture they receive. The wettest area is in Cherrapunji, India, where the forest receives more than 400 inches of rain per year. In contrast to the temperate forest, the seasons in the tropical rain forest are determined primarily by the amount of rainfall. Thus, there is a wet and a dry season. However, some tropical forests have no dry season at all, since there are constant drenchings.

There are many other differences between tropical rain and temperate forests. Whereas, a temperate forest has very few species, in a square mile of the Amazon rain forest more than 3,000 species of plants exist. In a temperate forest there are large stands of one species of tree, but in a tropical forest no one species dominates. The more common scenario is for there to be just a few individual plants from each species.

Also in contrast to a temperate forest, only 1 to 3 percent of the sunlight ever reaches the rain forest floor. Therefore, there is comparatively little undergrowth in a tropical forest. This actually makes such a forest an easy one through which to walk.

The soil in the tropics is very poor indeed, for the heavy rains wash away much of the vital nutrients. The dead leaves and animals that are not washed away are quickly decomposed by the bacteria and fungi in the soil. These decomposers work so well that almost no dead matter remains on the ground for more than twenty-four hours. In order to catch the nutrients that do exist, tropical plants have shallow roots that immediately soak up any nutrients available.

Like the tropical rain forest, the light tropical forest, including the monsoon forests of tropical Asia, occur in humid tropical climates. However, the light tropical forest experiences a pronounced dry season. Most species exhibit special adaptations for passing the dry season in much the same manner as temperate zone species pass the winter. In the light tropical forest of Panama the palms and other understory trees retain their leaves, but the tall emergent trees lose their leaves during the dry season. The number of animals species is second only to that of the rain forests.

With a further decrease in rainfall, tropical scrub or thornwood areas appear. The rainfall is not only moderate in amount, but both imperfect and irregular in distribution. These forests contain small hardwood trees often grotesquely twisted and thorny. They either occur in dense stands or in a scattered or clumped pattern. The leaves are small and shed during dry seasons.

Tropical savannas receive from 40 to 60 inches of rainfall, but have one or two prolonged dry seasons when fires are an important part of maintaining the dominant grass cover. The grasslands have only scattered trees or clumps of trees. Single species of both grass and trees are often dominant over large areas.

The African tropical savanna is one of the most familiar worldwide because it is "big game" country. The most well-known area is that of the Serenghetti Plain in Tanzania. As one would expect, there is a tremendous number and variety of hoofed mammals on this plain, and, therefore, a tremendous number of predators, including lions, leopards, cheetahs, and hyenas. The largest areas of tropical savannas are in central and east Africa, but sizable tropical savannas or grasslands also occur in South America and Australia.

Irregular annual rainfall of only 20 to 40 inches along with prolonged periods of low relative humidity produce the Mediterranean or chaparral biome. In this type of climate there is no really cold season and spring is the main growing and flowering season. The summers are hot and dry, and the winters warm and wet. The plants that grow here are usually low and shrubby and have leaves that are usually small, tough and leathery, and glossy from wax coverings on the upper surfaces. Their trunks are often clad in thick bark to protect the vital growing processes within from excessive dry heat. Unfortunately, most of the original forest vegetation around the Mediterranean has been destroyed. The original zonal vegetation was a canopy of holm oak (Quercus ilex) often interspersed with the Aleppo pine (Pinus halepensis).

Deserts are areas of very low annual rainfall, usually of less than ten inches. The high temperatures rapidly evaporate whatever rain the areas manage to receive, making only a very small proportion of the total actually available to plants. Making it even more difficult for life to survive, from a third to a half of the annual precipitation may occur during a single cloudburst. Both plants and animals in the desert are adapted to the scarcity of water.

Most of the world's deserts straddle the Tropic of Cancer or the Tropic of Capricorn. The reason for this is that as the air rises from the hot equatorial regions, it expands, drops its moisture as rain, and spreads northward and southward away from the equator. The air is now very dry, but it is also cooler. Cool air is heavier and therefore settles back toward earth. The descending air warms and so can therefore hold more moisture. So, by the time the equatorial air reaches the Tropics of Capricorn and Cancer there is little moisture left in it.

Temperate grasslands receive between 10 and 30 inches of rain. This biome has large areas of grassland with very few trees. Large grassland areas occupy the interior of the North American and Eurasian continents, southern South America (the Argentine pampas), and Australia. As one might think from the presence of so many grasses, the dominant animals are large herbivores (i.e. plant eaters). These include the bison, antelope, and kangaroos. Also present are many burrowing animals such as ground squirrels and prairie dogs.

Temperate deciduous forests receive abundant rainfall varying from 30 to 60 inches (75 to 150 cm), but the temperatures are moderate and have a distinct seasonal pattern. These forests are characterized by deciduous forest communities. There are many fruit and nut trees and the herb and shrub layers tend to be well developed. Also well developed is the soil life. Animals include white-tailed deer, bear, gray and fox squirrels, gray fox, and bobcat. The common birds of the tall trees from top to bottom are the scarlet tanager, red-eyed vireo, redstart, eastern wood peewee, and black and white warbler. At the bottom may be found such birds as the Kentucky warbler and ovenbird. In the smaller trees are found the yellow warbler. These forests are found in eastern North America, all of Europe, and parts of Japan, Australia, and the tip of South America.

Northern coniferous or boreal forests are cooler and receive less rainfall. They are also subject to pronounced seasonality. The typical tree is some type of needle-leaved evergreen tree, especially spruce, fir, and pine. These trees form such an extensive canopy that the resulting dense shade inhibits the growth of shrub and herb layers. These forests are often subject to attacks by bark beetles and defoliating insects such as sawflies and budworms. One of the largest animals here is the moose. Small mammals include the snowshoe hare, red and gray squirrel, opossum, spruce mouse, and golden chipmunk. The birds are the grouse, along with siskins and crossbills. These forests stretch across both North America and Eurasia.

Tundra is found in the Arctic and alpine areas in and around the polar ice cap areas. Low temperatures and a short growing season make for a lack of trees in this biome. All but the upper few inches of ground remains frozen during the summer. The permanently frozen deeper soil is called permafrost. The tundra is essentially a wet arctic grassland with vegetation consisting of grasses, sedges, dwarf woody plants, and lichens ("reindeer moss") on drier locations. There are several different types of tundra depending on the amount of available moisture. These are the wet, rain, moist, and dry tundras.

General Patterns

The information about the world's climate and vegetation patterns can be put together into what can be referred to as a roller coaster model of the biomes. The model has three peaks. The middle peak is located where the equator, and, hence, the tropical rain forest, is located. Proceeding north or south from the equator towards the low point of the tropics of Capricorn and Cancer, the heat and rain lessen resulting in lower heights of the upper canopy trees. As these trees decrease in height, the understory trees become more prominent. Also the other forest levels become more prominent. With further lessening in heat and moisture the trees become more scattered and the grasslands become prominent, eventually leading to desert.

Going north and south from the low point of the deserts the pattern just described goes in reverse (with the exception that there is less rainfall in the boreal than in the temperate forest). The trees become more prominent until they reach their maximum heights in the boreal forests in

Roller Coaster Model (tall trees to smaller ones to shrubs to herbs to desert):

The biomes:

bf trf bf
rt c lrf lrf c rt
cb tws tws cb wt
wt ws ws ws ws
mt p s s p mt
dry tundra desert desert dry tundra

TRF = tropical rain forest CB = coniferous & broad-leaved

LTRF = light tropical rain forest RT = rain tundra

TWS = tropical woodland and shrub WT = wet tundra

WS = wooded shrub MT = moist tundra

S = savanna; P = prairie; C = coniferous (fir/spruce); BF = boreal forest

the northern and southern hemispheres. Proceeding toward the poles from the boreal forest north and south respectively, the tree heights gradually lessen again. A polar desert (the tundra) gradually replaces the trees.

Impact of Ecology on Human Civilizations

The importance of the model of the world's biomes is that it helps explain why civilizations developed in some areas of the world and not others. It also helps account for the varying environments facing humans in the different biomes, that in turn led to differentiations in human societies. The next chapter dealing with the ecological sources of human conflict, will show that the origins of these conflicts are largely due to differences in the character of ecological barriers in the world's regions.

Many persons are interested in why civilizations decline after having been established for a long time. The reasons seem to be a nice summary of the points made so far in the book and points that will be made in future chapters. A civilization builds as it organizes to take advantage of the natural resources available in an area. In the simple agricultural civilization, solutions to agricultural problems are invented that feeds a large scale population. In more technologically advanced societies, other systems, including vast trading networks, are worked out in order to support large scale population. As the civilization works out more productive techniques that often give it the economic edge over competing areas or older civilizations, it works out an economic, social, and political hierarchy. This hierarchy fosters flattering ideologies that praise the organizing principles of the society. The hierarchy then comes to have vested interests in continuing the situation as it is, and it resists change. Rival areas start to develop and gain insight from the technologies of the dominant civilization. The rival civilization comes from an area where the natural resources have not yet been utilized. Adapting the new technologies and adding onto them creates a more sophisticated civilization. In competition with the older civilization that cannot change because of the social divisions within that society, the new civilization has all the advantages and surpasses the older civilization, which then goes into relative decline. Once weakened, some of the declines of the older civilizations are quite dramatic as in the abandonment of Mayan higher civilization within the space of one hundred years. Then the pattern begins anew with the newer civilization establishing a well-instituted social hierarchy with privileges that become ordained by religion and other philosophies. This then will make it difficult for the newer civilization to compete with its upcoming rivals in previously relatively unexploited areas. This situation certainly seems to fit the United States of America with its social refusal to adapt to the challenges of new ways of life presented by more socially cooperative societies.

The above theory ties in very nicely with the thesis that man is an animal, and subject to animals drives and passions. Man, like other animals, is very selfish and has to work at being more cooperative. As previously said, the key difference between man and animal is that man can justify his social hierarchy, despite its cruelties and injustices.

The ecological perspective, modified by the selfish nature of humans, is superior to the Western perspective of culturism that praises the culture of the West. World history is still very much the realm of Western history in America with subtle or not so subtle praise of the Western heritage. The culturalism is not at all subtle in the choosing of such civilizations as Egypt and Mesopotamia as Western predecessors. Somewhat unconsciously Western historians looked around for the most prominent civilizations near Europe and then declared these to be their cultural ancestors. World history ought to be just that: world history. It should not be Western history parading as world history. Western history should be clearly labeled Western history to avoid culturalism. But, proving the point about the nature of man and society, most white Americans oppose any such change as they feel they have to defend their position as superior cultural beings against alternative views that are both more accurate and fair.


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