Chapter 5: Outlines and Concept Maps
Lab Activity 24: More Concept Maps
To map the major and minor details supporting a central idea.
Step 2: Read the continuation of the passage from the college biology textbook Essential Biology, and then answer the questions that follow it. After you have answered the questions, return to the Lab Manual to complete Step 3.
The Three Main Causes of the Biodiversity Crisis
1 Habitat Destruction Human alteration of habitats poses the single greatest threat to biodiversity throughout the biosphere. Assaults on diversity at the ecosystem level result from the expansion of agriculture to feed the burgeoning human population, urban development, forestry, mining, and environmental pollution. The amount of human-altered land surface is approaching 50%, and we use over half of all accessible surface fresh water. Some of the most productive aquatic habitats in estuaries and intertidal wetlands are also prime locations for commercial and residential developments. The loss of marine habitats is also severe, especially in coastal areas and coral reefs.
2 Introduced Species Ranking second behind habitat loss as a cause of the biodiversity crisis is human introduction of exotic (non-native) species that eliminate native species through predation or competition. For example, if your campus is in an urban setting, there is a good chance that the birds you see most often as you walk between classes are starlings, rock doves (often called "pigeons"), and house sparrows—all introduced species that have replaced native birds in many areas of North America. One of the largest rapid-extinction events yet recorded is the loss of freshwater fishes in Lake Victoria in East Africa. About 200 of the 300 species of native fishes, found nowhere else but in this lake, have become extinct since Europeans introduced a non-native predator, the Nile perch, in the 1960s.
3 Overexploitation As a third major threat to biodiversity, overexploitation of wildlife often compounds problems of shrinking habitat and introduced species. Animal species whose numbers have been drastically reduced by excessive commercial harvest or sport hunting include whales, the American bison, Galápagos tortoises, and numerous fishes. Many fish stocks in the ocean have been overfished to levels that cannot sustain further human exploitation. In addition to the commercially important species, members of many other species are often killed by harvesting methods; for example, dolphins, marine turtles, and seabirds are caught in fishing nets, and countless numbers of invertebrates are killed by marine trawls (big nets). An expanding, often illegal world trade in wildlife products, including rhinocerous horns, elephant tusks, and grizzly bear gallbladders, also threatens many species.
—Campbell, Reece, & Simon, Essential Biology, 2e, p. 454.
Copyright © 1995-2010 by Pearson Education, Inc., publishing as Pearson Longman. Legal Disclaimer