Chapter Summary: Chapter 4
Community Ecology, Population Ecology, and the Human Population
4-1 What roles do species play in an ecosystem?
All different types of species in a community—native, non-native, indicator, exotic, and alien—play specific roles in
its ecology. CONCEPT 4-1A Each species plays a specific ecological role called its niche. CONCEPT 4-1B Any
given species may play one or more of five key roles—native, nonnative, indicator, keystone, or foundation—in a
particular ecosystem.
1. Define ecological niche. Distinguish between a specialist and a generalist. Evaluate the conditions that
favor these two approaches.
2. Explain the difference between a niche and a habitat.
3. Distinguish among the following roles played by species and give one example of each: native species,
nonnative species, indicator species, keystone species, and foundation species. Explain why these
labels are important.
4-2 How do species interact?
CONCEPT 4-2 Five types of species interactions—competition, predation, parasitism, mutualism, and
commensalism — affect the resource use and population sizes of the species in an ecosystem. Over a long time
scale, populations of some species develop adaptations to help them use shared resources at different times, in
different ways, or in different places – a process called resource partitioning.
4. Why and how does resource partitioning occur?
5. Distinguish between a predator and a prey, and give an example of a predator-prey relationship. How
does this relationship contribute to population management?
6. Distinguish among three forms of symbiotic relationships and give one example of each: parasitism,
mutualism, and commensalism.
4-3 How do communities and ecosystems respond to changing environmental conditions?
CONCEPT 4-3 The structure and species composition of communities and ecosystems change in response to
changing environmental conditions through a process called ecological succession. Scientists currently believe that
ecological succession is an ongoing struggle for resources, and that even late-successional communities are in a
continual state of flux.
7. Define ecological succession. Distinguish between primary and secondary succession, giving an
example of each.
4-4 What limits the growth of populations?
Biotic potential together with environmental resistance determine the carrying capacity of a habitat – the maximum
population of a given species that the habitat can sustain indefinitely. CONCEPT 4-4 No population can continue to
grow indefinitely because of limitations on resources and because of competition among species for those resources.
Population crash (dieback) can occur if a population exceeds the carrying capacity of its environment.
8. Explain the concepts of biotic potential, intrinsic rate or increase, environmental resistance, and
carrying capacity. Using these concepts, explain why there are always limits to population growth in
nature.
9. Differentiate between exponential growth and logistic growth of populations.
10. Briefly explain why humans are not exempt from nature’s population controls.
11. Distinguish between opportunists and competitor species. How are their reproductive rates different?
4-5 What factors influence the size of the human population?
Expansion of habitat, emergence of modern agriculture, and development of sanitation, antibiotics, and vaccines
have all contributed to the expansion of the human population in the last 200 years. CONCEPT 4-5A Population
size increases because of births and immigration, and decreases through deaths and emigration. CONCEPT 4-5B
The average number of children born to women in a population (total fertility rate) is the key factor that determines
population size. An array of social, economic, and health factors contributes to the TFR of a given country.
CONCEPT 4-5C The numbers of males and females in young, middle, and older age groups determine how fast a
populations grows or declines.
12. Define birth rate, death rate. Write an equation to mathematically describe the relationship between
these rates and the rate of population change.
13. Distinguish between replacement-level fertility and total fertility rate. Describe how these fertility rates
affect population growth.
14. What factors affect birth rates and fertility rates?
15. Why is infant mortality rate a key measure of a society's quality of life?
16. How does age structure impact a society? What is the impact of a rapid population decline, especially
when that is focused in a single age group?
4-6 How can we slow human population growth?
As the world's population grows, debates about interactions among population growth, economic growth, politics,
and moral beliefs are some of the most important environmental questions being addressed today. As countries
develop, they undergo demographic transition, resulting in slowed population growth. CONCEPT 4-6 We can slow
human population growth by reducing poverty, elevating the status of women, and encouraging family planning.
17. List the four stages of the demographic transition. List social, biological, political, and economic issues
that can be addressed to help developing countries undergo a demographic transition.
18. What is the connection between a woman's birth rate and her access to education and social/economic
opportunities?
19. What is family planning? Describe the roles of family planning.
20. Compare and evaluate the population policies of China and India.
21. What are the key approaches (as identified by the United Nations Conference on Population and
Development) to slowing population growth?