Global Change - Environmental Science - page 196

• Introduced species
• Endangered and extinct species
• Habitat loss
Losses Due to Overuse and Overexploitation
Overexploitation of species creates loss of biodiversity. Among the most common overused and overexploited
groups of species are marine fish and invertebrates. Overexploitation, including overfishing and over-harvest-
ing, has resulted in 75 percent of the world's marine species being depleted. Several species—including cod off
Newfoundland in Canada, anchovy off the coast of Peru, sole in the Irish Sea, and deep-sea fish such as orange
roughy and sablefish—have been depleted to such an extent that they are no longer a viable food or economic
resource. Nearly 100 million tons of fish and shellfish are removed from the world's oceans every year. As the
world's population grows and as diets increasingly shift from beef and pork to more fish and shellfish, even
more fish and shellfish will be removed. Overfishing also impacts species, such as dolphins and seals, which
are caught unintentionally as part of netting or long-lining techniques. So-called bycatch is thrown away when
fish are harvested. For every pound of shrimp catch, over 5 pounds of bycatch is discarded. The loss of marine
life impacts the world's coastal populations (nearly 2 billion people), many of whom depend upon marine life
for food and other products.
Aquatic species are not alone in their growing use. Worldwide beef consumption doubled from 1950 to 2000,
from approximately 44 pounds per capita to nearly 88 pounds per capita. The acreage needed to grow beef is
immense. Land is needed to grow food (usually corn) to feed the cattle, and land is needed to house the cattle
until they are taken to market. Many corporations that use beef in their fast-food restaurants have cut down
large areas of trees in the tropical rain forest to meet the needs of beef production.
Losses Due to Pollution
Pollution comes in five primary forms: air, soil, water, noise, and light. Humans release pollutants into the
Earth's atmosphere, soil, or natural water systems, causing degradation in both local areas and sources to which
pollution can be transported. Light and noise pollution can interfere with the natural cycles of species and ad-
versely affect behavior. A sixth form of pollution, genetic pollution, is still under investigation.
Pollutants can have many negative affects on animal species: interfering with metabolic and endocrine func-
tions, impairing development, shortening life spans, and compromising immune systems. Pollutants also can
alter species' reproductive function, causing changes in mating behaviors, genetically affecting offspring, or
causing an organism to become sterile. Pollution is often a contributing factor in the decline or ultimate extinc-
tion of a species. The loss of one species then has a ripple effect throughout an ecosystem.
There are many mechanisms by which pollutants enter species: through the air they breathe, the water they
drink, the food they digest, or through their skin percutaneously. Marine fish and other aquatic species are es-
pecially defenseless when exposed to pollutants in the water. Air pollutants include carbon monoxide, sulfur
dioxide, and oxides of nitrogen. Water and soil pollutants include heavy metals, pesticide and herbicide com-
pounds, and the thermal pollution of man-made heat sources.
Plant species also can be adversely affected by pollutants. Lichen is especially fragile and, thus, susceptible to
destruction by air pollutants. Therefore, the presence of lichen is often a good indicator of clean air. Air pol-
lutants also can cause damage to the water and soil, frequently in the form of adjusting the pH level. When an
air pollutant, such as sulfuric acid, combines with the water droplets that make up clouds, the water droplets
become acidic. Acid rain causes harm to living organisms. When those droplets fall to the ground as rain or