Cracking the AP Biology Exam

13

Animal Behavior and Ecology

HUMAN IMPACT ON THE ENVIRONMENT

Unfortunately, humans have disturbed the existing ecological balance, and the results are far-reaching. Soils have been eroded and various forms of pollution have increased. The potential consequences on the environment are summarized below:

  • Greenhouse effect—The increasing atmospheric concentrations of carbon dioxide through the burning of fossil fuels and forests have contributed to the warming of the earth. Higher temperatures may cause the polar ice caps to melt and flooding to occur. Other potential effects of global warming include changes in precipitation patterns, changes in plant and animal populations, and detrimental changes in agriculture.
  • Ozone depletion—Pollution has also led to the depletion of the atmospheric ozone layer by such chemicals as chlorofluorocarbons (CFCs), which are used in aerosol cans. Ozone (O3), forms when UV radiation reacts with O2. Ozone protects the earth’s surface from excessive ultraviolet radiation. Its loss could have major genetic effects and could increase the incidence of cancer.
  • Acid rain—The burning of fossil fuels produces pollutants such as sulfur dioxide and nitrogen dioxide. When these compounds react with droplets of atmospheric water in clouds they form sulfuric and nitric acids, respectively. The rain that falls from these clouds is weakly acid and is called acid rain. Acid rain lowers the pH of aquatic ecosystems and soil which damages water systems, plants and soil. For example, the change in soil pH causes calcium and other nutrients to leach out, which damages plant roots and stunts their growth. Furthermore, useful microorganisms that release nutrients from decaying organic matter into the soil are also killed, resulting in less nutrients being available for the plants. Low pH also kills fish, especially those that have just hatched.
  • Desertification—When land is overgrazed by animals, it turns grasslands into deserts and reduces the available habitats for organisms.
  • Deforestation—When forests are cleared (especially by the slash and burn method), erosion, floods, and changes in weather patterns can occur.
  • Pollution—Another environmental concern is the toxic chemicals in our environment. One example is DDT, a pesticide used to control insects. DDT was overused at one time and later found to damage plants and animals worldwide. DDT is particularly harmful because it resists chemical breakdown and today it can still be found in the tissues of nearly every living organism. The danger with toxins such as DDT is that as each trophic level consumes DDT, the substance becomes more concentrated by a process called biomagnification.
  • Reduction in biodiversity—As different habitats have been destroyed, many plants and animals have become extinct. Some of these plants could have provided us with medicines and products that may have been beneficial.