Population Ecology

Environmental Influence

Local population characteristics are often influenced in a possibilistic manner by the availability of resources. In the middle latitudes, population densities tend to be greatest where the terrain is level, the climate is mild and humid, the soil is fertile, mineral resources are abundant, and the sea is accessible. Conversely, population tends to thin out with excessive elevation, aridity, coldness, ruggedness of terrain, and distance from the coast.

Climatic factors influence where people settle. Most of the sparsely populated zones in the world have, in some respect, “defective” climates from the human viewpoint (see Figure 3.1). The thinly populated northern edges of Eurasia and North America are excessively cold, and the belt from North Africa into the heart of Eurasia matches the major desert zones of the Eastern Hemisphere. Humans remain creatures of the humid and subhumid tropics, subtropics, or midlatitudes and have not fared well in excessively cold or dry areas. Small populations of Inuit (Eskimo), Sami (Lapps), and other peoples live in some of the less hospitable areas of Earth, but these regions do not support large populations. Humans have proven remarkably adaptable, and our cultures contain strategies that allow us to live in many different physical environments, but perhaps, as a species, we have not entirely moved beyond the adaptive strategies that suited us so well to the climatic features of sub-Saharan Africa, where we began.

Humankind’s preference for lower elevations is true especially for the middle and higher latitudes. Most mountain ranges in those latitudes stand out as sparsely populated regions. By contrast, inhabitants of the tropics often prefer to live at higher elevations, concentrating in dense clusters in mountain valleys and basins. For example, in tropical portions of South America, more people live in the Andes Mountains than in the nearby Amazon lowlands. The capital cities of many tropical and subtropical nations lie in mountain areas above 3000 feet (900 meters) in elevation. Living at higher elevations allows residents to escape the humid, hot climate and diseases of the tropic lowlands. In addition, these areas were settled because the fertile volcanic soils of these mountain valleys and basins were able to support larger populations in agrarian societies.

Many humans live near the sea. Eurasia, Australia, and South America resemble hollow shells, with the majority of the population clustered around the rim of each continent (see Figure 3.1). In Australia, half of the population lives in only five port cities, and most of the remainder is spread out over nearby coastal areas. This preference for living by the sea stems partly from the trade and fishing opportunities the sea offers. At the same time, continental interiors tend to be regions of climatic extremes. For example, Australians speak of the “dead heart” of their continent, an interior land of excessive dryness and heat.

Disease also affects population distribution. Some diseases attack valuable domestic animals, depriving people of food and clothing resources. Such diseases have an indirect effect on population density. For example, in parts of East Africa, a form of sleeping sickness attacks livestock. This particular disease is almost invariably fatal to cattle but not to humans. The people in this part of East Africa depend heavily on cattle, which provide food, represent wealth, and serve a religious function in some tribes. The spread of a disease fatal to cattle has caused entire tribes to migrate away from infested areas, leaving those areas unpopulated.

Environmental Perception and Population Distribution

Perception of the physical environment plays a major role in a group’s decision about where to settle and live. Different cultural groups often see the same physical environment in different ways. These varied responses to a single environment influence the distribution of people. A good example appears in a part of the European Alps shared by German- and Italian-speaking peoples. The mountain ridges in that area—near the point where Switzerland, Italy, and Austria border each other—run in an east-west direction, so that each ridge has a sunny south-facing slope and a shady north-facing one. German-speaking people, who rely on dairy farming, long ago established permanent settlements some 650 feet (200 meters) higher on the shady slopes than the settlements of Italians, who are culturally tied to warmth-loving crops, on the sunny slopes. This example demonstrates how contrasting cultural attitudes toward the physical environment and land use affect settlement patterns.

Sometimes a single cultural group changes its perception of an environment over time, with a resulting redistribution of its population. The coalfields of western Europe provide a good case in point. Before the industrial age, many coal-rich areas—such as the Midlands of England, southern Wales, and the lands between the headwaters of the Oder (or Odra) and Vistula rivers in Poland—were only sparsely or moderately settled. The development of steam-powered engines and the increased use of coal in the iron-smelting process, however, created a tremendous demand. Industries grew up near the European coalfields, and people flocked to these areas to take advantage of the new jobs. In other words, once a technological development gave a new cultural value to coal, many sparsely populated areas containing that resource acquired large concentrations of people.

Recent studies indicate that much of the interregional migration in the United States today is prompted by a desire for a pleasant climate and other desirable physical environmental traits, such as beautiful scenery. Surveys of immigrants to Arizona revealed that its sunny, warm climate is a major reason for migration. An attractive environment provided the dominant factor in the growth of the population and economy of Florida. The most desirable environmental traits that serve as stimulants for American migration include (1) mild winter climate and mountainous terrain, (2) diverse natural vegetation that includes forests and a mild summer climate with low humidity, (3) lakes and rivers, and (4) nearness to the seacoast. Different age and cultural groups often express different preferences, but all are influenced by their perceptions of the physical environment in making decisions about migration.

Population Density and Environmental Alteration

People modify their habitat through their adaptive strategies. Particularly in areas where population density is high, radical alterations often occur. This can happen in fragile environments even at relatively low population densities because, as discussed earlier in this chapter, Earth’s carrying capacity varies greatly from one place to another and from one culture to another.

Many of our adaptive strategies are not sustainable. Population pressures and local ecological crises are closely related. For example, in Haiti, where rural population pressures have become particularly severe, the trees in previously forested areas have been stripped for fuel, leaving the surrounding fields and pastures increasingly denuded and vulnerable to erosion (Figure 3.20). In short, overpopulation relative to available resources can precipitate environmental destruction—which, in turn, results in a downward cycle of worsening poverty, with an eventual catastrophe that is both ecological and demographic. Thus, many cultural ecologists believe that attempts to restore the balance of nature will not succeed until we halt or even reverse population growth, although they recognize that other causes are at work in ecological crises.

Overpopulation and deforestation. This aerial photograph depicts the border between Haiti and the Dominican Republic. The two nations share the Caribbean island of Hispaniola. Population pressures in Haiti, on the left side of the photograph, have led to deforestation; the Dominican Republic is the greener area to the right. The political border is also an environmental border. (NASA.)

Thinking Geographically

Question

rh+6IY0djmbmhe2ePTliacvXJfjZD6erZdt4gPc8wd81blY/hGJskDnhrz2W1Ex+/axvnmftJVV/DnHGEJ5KHhr2j+BQqadsnGiut7OueVo9696rMtSwnVZze/oq1CJahiuNrDe1WkvoY7QPQvazUp8V0wyQ1xQAuLfU8QtBdGwnTPzqYZ6MD9qI0jdyeuinhfGy5FRwgLU6Hk5/87q3PqBOalopzv30jGLArRta8l3+5Ytw

The worldwide ecological crisis is not solely a function of overpopulation. A relatively small percentage of the Earth’s population controls much of the industrial technology and consumes a disproportionate percentage of the world’s resources each year. Americans, who make up less than 4.5 percent of the global population, account for about 23 percent of the natural resources consumed globally each year. New houses built in the United States in 2009 were, on average, 46 percent bigger than those built in 1960, despite a shrinking average household size during that period. If everyone in the world had an average American standard of living, Earth could support only about 1.5 billion people—only 21 percent of the present global population. As the economies of large countries such as India and China continue to surge, the resource consumption of their populations is likely to rise as well because the human desire to consume appears to be limited only by the ability to pay for it.