Page 91 - Environment: The Science Behind the Stories

• The fossil record informs us about life’s history (pp. Assess logistic growth, carrying capacity, limiting
73, 74) factors, and other fundamental concepts in population
ecology
Discuss reasons for species extinction and mass • Populations unrestrained by limiting factors will undergo
extinction events exponential growth. (pp. 84–85)

• Extinction may occur when species that are highly special- • Logistic growth describes the effects of density-dependent
ized or that have small populations encounter rapid envi- limiting factors; growth slows as population size increases,
ronmental change. (p. 77) and population size levels off at a carrying capacity. (p. 85)

• Earth’s life has experienced five known episodes of mass • Carrying capacity is the maximum size a population
extinction, due to asteroid impact and possibly volcanism can attain over the long term in a given environment.
and other factors. (p. 77) (pp. 85–86)
• Today, human impact may be initiating a sixth mass extinc- • K-selection and r-selection describe theoretical endpoints
tion. (pp. 77–78) in how organisms can allocate growth and reproduction.
(pp. 86–87)
List the levels of ecological organization
• Ecologists study phenomena on the organismal, popula- Identify efforts and challenges involved in the
tion, community, and ecosystem levels—and, increasingly, conservation of biodiversity
at the level of the biosphere. (pp. 78–79) • Social and economic factors influence our impacts on natu-
• Habitat, niche, and specialization are important ecological ral systems in complex ways. (p. 87)
concepts. (p. 79) • Introduced species are one of many impacts that affect native
species and systems, particularly on islands. (pp. 87–88)
Outline the characteristics of populations that help
predict population growth • Extensive efforts to protect and restore species and habi-
tats are needed to prevent further erosion of biodiversity.
• Populations are characterized by population size, popu- (p. 88)
lation density, population distribution, sex ratio, and age
structure. (pp. 80–81) • Climate change is challenging the effectiveness of pro-
tected areas. (pp. 88–89)
• Birth and death rates, as well as immigration and emigration,
determine how a population will grow or decline. (p. 84)

testing your Comprehension

1. Explain the premises and logic that support the concept of 7. List and describe each of the five major population char-
natural selection. acteristics discussed. Briefly explain how each shapes
2. Describe two examples of evidence for natural selection. population dynamics.
3. Differentiate between allopatric and sympatric speciation. 8. Differentiate between exponential and logistic growth
curves. Give examples of the conditions under which
4. Compare and contrast species extinction and mass extinc- each would occur.
tion events. For each, give examples.
9. Describe how limiting factors relate to carrying capacity.
5. What is the difference between a species and a popula-
tion? Between a population and a community? 10. Explain the difference between K-selected species and
r-selected species. For each, give an example that was not
6. Define and contrast the concepts of habitat and niche.
mentioned in the chapter.

seeking solutions

1. In what ways has artificial selection changed people’s 2. In your region, what species are threatened with extinc-
quality of life? Give examples. How might artificial tion? What reasons lie behind their endangerment? Sug-
selection be used to improve our quality of life further? gest steps that could be taken to bolster their populations.
Can you envision a way it could be used to reduce our 3. Do you think the human species can continue raising its
90 environmental impact? global carrying capacity? How so, or why not? Do you

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