Threats to biodiversity

For more than 99% of its species history, H. sapiens existed in small groups of hunter-gathers, a highly intelligent primate that learned to exploit virtually every terrestrial environment that existed on Earth. About 8,000-12,000 years ago, however, people largely ceased living within the constraints of given ecosystems and became ecosystem-creators. The rise of agriculture drastically altered the earth's carrying capacity for H. sapiens, and human populations could increase. For several thousand years after our species became essentially an agricultural granivore, populations of H. sapiens were held in check by occasional famine and by the infectious diseases that co-evolved with densely packed agricultural humanity. However, beginning in the eighteenth century, scientific and technological advances led to increases in agricultural productivity and (temporary?) conquest of many infectious diseases. During the nineteenth and twentieth centuries, human populations grew exponentially, expanding from approximately 1 billion in 1850 to about 6.3 billion in July 2003. Furthermore, at the same time that human populations were increasing so dramatically, each person was, on average, using a greater portion of the world's natural resources. As a result, Wise or Knowing Man has had a devastating impact on most natural systems throughout the world.

Humans dominate the global ecosystem in four primary ways:

• Direct transformation of about half the earth's ice-free land for human use. Houses, cities, roads, strip-mines, shopping malls, and highways involve obvious land transformations. Even more surface area is occupied by agricultural systems hostile to almost all living organisms except the monocultural domesticates being produced for food or fiber.

• Alteration of the nutrient cycles within the world ecosystem. Globally, the release of nitrogen—through the consumption of fossil fuels and use nitrogen-based fertilizers—is the most critical, though introduction or extraction of other nutrients may be locally important.

• Disruption of the atmospheric carbon cycle, particularly through the consumption of fossil fuels. This is the primary cause of anthropogenic climate change.

• Introduction of pollutants into the world ecosystem. To this point pollution has had far less impact than the three factors listed above. However, some scientists believe that the accelerated release of pesticides, industrial wastes, and other bioactive chemicals may have increasingly severe ecological consequences. Furthermore, in a world of economic inequality and political instability, a massive infusion of nuclear pollutants is a possibility that should not be discounted.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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