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 different 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.
Distinguish between a predator and a prey, and give an example of a predator-prey relationship.
4-2 How do species interact?
Species that share limited resources interact in five basic ways through competition, predation, parasitism, mutualism, and commensalism.
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.
5.
List two strategies that predators use to capture their prey. List at least five strategies that prey use to defend themselves against predators.
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?
When environmental conditions change, one group of species is replaced by another through primary ecological succession and secondary ecological succession. CONCEPT 4-3 The structure and species composition of ecosystems change in response to changing environmental conditions through a process called ecological succession.
7.
Define ecological succession . Distinguish between primary and secondary succession, giving an example of each.
8.
List and briefly describe three ways humans affect communities.
4-4 What limits the growth of populations?
As a population reaches its carrying capacity, its growth rate will decrease; as it faces environmental pressure, the growth will be logistic growth.
CONCEPT 4-4 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.
9.
Distinguish among the biotic potential, intrinsic rate or increase, environmental resistance, carrying capacity, exponential growth, and logistic growth of a population and use these concepts to explain why there are always limits to population growth in nature.
10.
Briefly explain why humans are not exempt from nature’s population controls.
4-5 What factors influence the size of the human population?
The size of a species’ population is influenced by the following four variables: births, deaths, immigration, and emigration. 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. CONCEPT 4-5C The numbers of males and females in young, middle, and older age groups determine how fast a populations grows or declines.
11.
Define birth rate, death rate . Write an equation to mathematically describe the relationship between these rates and the rate of population change.
12.
Distinguish between replacement-level fertility and total fertility rate . Describe how these fertility rates affect population growth.
4-6 How can we slow human population growth?

Lessons from ecology can help us in sustaining the earth as we live upon it.
CONCEPT 4-6 Experience indicates that the most effective ways to slow human population growth are family planning, reducing poverty, and elevating the status of women.
13.
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.
14.
What is family planning? Describe the roles of family planning.
15.
Compare and evaluate the population policies of India, China, and Thailand.