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abiotic factors 81 biomass 94 biotic factors 81 carbon cycle 96 carnivore 92 coevolution 86 commensalism 89 community 91 competition 88 competitive exclusion principle 88 consumer 92 decomposer 92 denitrifying bacteria 98 detritus 94 ecology 81 ecosystem 91 ectoparasite 89 endoparasite 89 environment 81 |
evolution 86 extinction 86 food chain 94 food web 94 free-living nitrogen-fixing bacteria 98 habitat 82 herbivore 92 host 88 interspecific competition 88 intraspecific competition 88 keystone species 92 limiting factor 82 mutualism 90 mycorrhizae 90 natural selection 85 niche 82 nitrogen cycle 98 nitrifying bacteria 98 nitrogen-fixing bacteria 98 |
omnivore 92 parasite 88 parasitism 88 predation 87 predator 87 prey 87 primary consumer 92 producer 92 range of tolerance 82 secondary consumer 92 speciation 86 species 84 symbiosis 88 symbiotic nitrogen-fixing bacteria 98 trophic level 93 vector 89 |
A change in the predator/prey relationship between orcas and otters is apparently affecting the sea otter population. This is especially important since sea otters are considered keystone species in the marine ecosystem. For more information on this relationship and how humans are playing the role of competitor in the interaction, read  Mysterious Disappearance of Sea Otters in Alaska. For a related story, check out
Judge Rules on Excessive Fishing in Alaska.Another keystone species, bison, are also affected by human interactions. Once bison leave Yellowstone Park, they are no longer protected and are actually targeted because bison are not supposed to roam freely outside the park. Why would we purposely destroy a keystone species? To further understand the reasons behind this controversial management policy, read Should Bison Leaving Yellowstone National Park Be Shot?What's large, brown, floats, and provides critical habitat and nutrients for hundreds of fish and invertebrates off the southern U.S. coast? Sargassum is a brown algae that grows in huge floating mats in the Atlantic Ocean. The U.S. agricultural community recognizes the nutritional value of the algae and uses it to feed hogs and cattle. This has led to competition and conflict. The controversial harvest of this habitat is further explained in Controversy over Algae Harvest and Habitat Conservation in the Atlantic. |
We know human activities impact nutrient cycles, but can people change food webs to benefit the ecosystem? Look at the
Food Web Control of Primary Production in Lakes case study for answers to these questions and more. Historically, we have manipulated populations and interactions among organisms for our benefit. Using drugs could be considered an example of how humans manipulate parasite populations. Drug-resistant Strain of Sleeping Sickness Appears in Ethiopia explains how this parasite population is "striking back" through natural selection.The dead zone in the Gulf of Mexico off the mouth of the Mississippi River is not alone. Another dead zone off the coast of North Carolina is the result of runoff from hog farms. Read N.C. Aquatic Dead Zone from Floods after Hurricane Floyd for this story.The Great Lakes are also suffering from runoff problems. In this chapter you read about organic contaminants in Great Lakes' fish and how these contaminants can influence human health. Now see the story of a contaminated river that empties into Lake Michigan. PCB Contamination in the Fox River case study.
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If you would like to check your understanding of the major roles of organisms in an ecosystem and how the roles correspond to the energy flow through an ecosystem, study the Energy Flow animation. |
Two more animations worth looking at are the Carbon Cycle and the Nitrogen Cycle. These animations illustrate how carbon and nitrogen cycle through ecosystems and how humans impact the flow of these materials.
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Review Questions |
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Critical Thinking Questions |
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