Thinking Scientifically

1. Many heavily polluted ecosystems are tainted with several types of pollutants. For example, several polar bears were recently discovered that are hermaphrodites – they have organs of both sexes. These bears also have high levels of PCBs in their blood, but researchers do not yet know whether exposure to PCBs is related to the disturbed sexual development. How could you link a particular chemical to a particular biological effect?

2. An approach to combat species invasion is to kill the invaders. In Hawaii, officials shoot feral cats, goats and pigs. In Australia, the government-added chlorine and copper to a bay to kill zebra mussels, killing everything living in the water. Do you think that this is an effective approach? Suggest an alternative.

3. Chapter 22 explained that if the number of species of mycorrhizal fungi in an ecosystem increases, then the number of plant species that they support increases. Does this finding support or challenge the diversity-stability hypothesis?

4. In the Aral Sea and in the Everglades, humans diverted natural water flow. Compare and contrast the effects of these actions in these two very different ecosystems.

5. How does desertification of the Sahara support the hypothesis that species invasion favors organisms that reproduce rapidly?

6. Select an ecosystem or biome from chapters 43 or 44, and list three ways that an earlier spring and later fall resulting from global climate change might affect its spectrum of species.

Additional Questions and Terms

1. Some companies have developed seeds that produce hardy crops, but do not leave usable seeds for the next season. Farmers are forced to buy their seeds from the company. Explain how this practice -- which may be outlawed by the time you read this -- counters sustainability.

2. Studies showing the response of bird populations in the U.K. to global warming used census data from 1971. Similarly, investigations of ozone depletion and UV-B levels in New Zealand relied on comparisons to decade-old census data. In studying ecosystem response to the oil spill in Prince William Sound, such census data was lacking. Why is the information important?