These days, of course, ecosystems are influenced not just by “natural” environmental stressors. In many situations, anthropogenic influences have become the most important constraining influence on the productivity of species and on ecosystems more generally. These direct and indirect influences have intensified enormously in modern times.

Humans affect ecosystems and species in three direct ways: (a) by harvesting valuable biomass, such as trees and hunted animals; (b) by causing damage through pollution; and (c) by converting natural ecosystems to into land-uses for the purposes of agriculture, industry, or urbanization.

These actions also engender many indirect effects. For example, the harvesting of trees alters the habitat conditions for the diversity of plants, animals, and microorganisms that require forested habitat, thereby affecting their populations. At the same time, timber harvesting indirectly changes functional properties of the landscape, such as erosion, productivity, and the quantity of water flowing in streams. Both the direct and indirect effects of humans on ecosystems are important.

Humans have always left “footprints” in nature – to some degree, they have always influenced the ecosystems of which they were a component. During most of the more than 100,000 years of evolution of modern Homo sapiens, that ecological footprint was relatively shallow. This was because the capability of humans for exploiting their environment was not much different from that of other similarly abundant, large animals. However, during the cultural evolution of humans, the ecological changes associated with our activities progressively intensified. This process of cultural evolution has been characterized by the discovery and use of increasingly more sophisticated methods, tools, and social organizations to secure resources by exploiting the environment and other species.

Certain innovations occurring during the cultural evolution of humans represented particularly large increases in capability. Because of their great influence on human success, these advances are referred to as “revolutions.” The following are examples of early technological revolutions:

· the discovery of ways of making improved weapons for hunting animals

· domestication of the dog, which also greatly facilitated hunting

· domestication of fire, which provided warmth and allowed for cooked, more digestible foods

· ways of cultivating and domesticating plants and livestock, which resulted in huge increases in food availability

· techniques for working raw metals into tools, which were much better than those made of wood, stone, or bone The rate of new discoveries has increased enormously over time. More recent technological revolutions include the following:

· methods of using machines and energy to perform work previously done by humans or draught animals

· further advances in the domestication and cultivation of plants and animals

· discoveries in medicine and sanitation

· extraordinary strides in communications and information-processing technologies

These and other revolutionary innovations all led to substantial increases in the ability of humans to exploit the resources of their environment and to achieve population growth. Unfortunately, enhanced exploitation has rarely been accompanied by the development of a compensating ethic that encourages conservation of the resources needed for survival. Even early hunting societies of more than about 10,000 years ago appear to have caused the extinction of species that were hunted too effectively.

The diverse effects of human activities on environmental quality are vital issues, and they will be examined in detail in later chapters. For now, we emphasize the message that intense environmental stress associated with diverse human activities has become the major factor causing ecological changes on Earth. Many of the changes are degrading the ability of the environment and ecosystems to sustain humans and their economies. Anthropogenic activities are also causing enormous damage to natural ecosystems, including to habitats needed to support most other species.

In fact, the environmental and ecological damage caused by humans has become so severe that an appropriate metaphor for the human enterprise may be that of a malignancy, or cancer. This is a sobering image. It is useful to dwell on it so that its meaning does not escape our understanding. Humans and their activities are endangering species and natural ecosystems on such a tremendous scale and rate that the integrity of Earth’s life-support systems is at risk.

From an ecological perspective, the pace and intensity of these changes is staggering. Moreover, the damage will become substantially worse before corrective actions are (hopefully) undertaken to reverse the damage and allow an ecologically sustainable human enterprise to become possible. From a pessimistic standpoint, however, it may prove to be beyond the capability of human societies to act effectively to fix the damage and to design and implement solutions for sustainability.

These are, of course, only opinions, albeit the informed views of many environmental specialists. Anticipating the future is always uncertain, and things may turn out to be less grim than is now commonly predicted. For example, we might be wrong about the availability of key resources needed to sustain future generations of humans. Still, the clear indications from recent patterns of change are that the environmental crisis is severe and that it will worsen in the foreseeable future.

But not all this damage is inevitable. There is sincere hope and expectation that human societies will yet make appropriate adjustments and will choose to pursue options that are more sustainable than many of those now being followed. In fact, no other outcome could be considered acceptable.

NOTE: Take Quiz 1.3 before proceeding to next lesson.