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CHAPTER 5
SPECIES INTERACTIONS, ECOLOGICAL SUCCESSION AND
POPULATION CONTROL
Outline
5-1 How do species interact?
A. Most species compete with one another for certain resources
1. There are five basic types of interaction between species when they share limited resources:
a. Interspecific competition occurs when two or more species interact to gain access to the
same limited resources.
3. When two species use the same resource, their niches overlap.
4. Resource partitioning occurs when species competing for similar scarce resources evolve
specialized traits that allow them to use shared resources at different times, in different ways,
or in different places.
B. Most consumer species feed on live organisms of other species.
1. Predation occurs when a member of one species (predator) feeds directly on all or part of a
living organism of another plant or animal species (prey), forming a predator-prey
relationship.
a. Herbivores can walk up to their prey.
b. Carnivores have a variety of methods to capture their prey, such as:
2. Prey have evolved ways to avoid predators.
a. Ability to run, swim, or fly fast; highly developed senses of sight or smell that alert them
to the presence of predators.
b. Physical protection such as shells, thick bark, spines, and thorns.
c. Camouflage.
3. SCIENCE FOCUS: Threats to kelp forests from predators and global warming.
a. Sea urchins and pollution threaten kelp forests.
b. Global warming threatens kelp forests.
C. Interactions between predator and prey species can drive each other’s evolution.
1. Coevolution occurs when two different species interact over a long period of time and
2. Some bats and moths have coevolved.
D. Some species feed off other species by living on or in them.
1. Parasitism occurs when one species (parasite) feeds on the body of, or the energy used by,
another organism (host), usually by living on or in the host.
3. Parasites can live the inside of the host, (e.g. tapeworms) or on the outside of the host (e.g.
mistletoe, sea lampreys).
E. In some interactions, both species benefit.
1. Mutualism occurs when two species behave in ways that benefit both by providing each with
F. In some interactions, one species benefits and the other is not harmed.
2. Epiphytes are plants that attach themselves to the trunks or branches of large trees for access
to sunlight; these represent commensalism.
5-2 How do communities and ecosystems respond to changing environmental conditions?
A. Communities and ecosystems change over time: ecological succession.
2. Primary ecological succession involves the gradual establishment of biotic communities in lifeless
3. Secondary succession occurs with a series of communities or ecosystems with different species
develop in places containing soil or bottom sediment. Such areas include:
a. Abandoned farmland.
B. Succession does not follow a predictable path.
1. The traditional view holds that succession proceeds in an orderly sequence along an expected path
until a certain stable type of climax community occupies an area.
2. The current view is that succession reflects an ongoing struggle by different species for resources
C. Living systems are sustained through constant change.
1. Living systems contain complex processes that interact to provide some degree of stability. This
2. One aspect of stability is inertia, or persistence, which is the ability of a living system, such as a
grassland or forest, to survive moderate disturbances.
1. A second aspect of stability is resilience, which is the ability of a living system to be restored
through secondary succession after a more severe disturbance.
5-3 What limits the growth of populations?
A. Populations can grow, shrink, or remain stable.
2. Population size may vary in cycles based on births, deaths, immigration, and emigration.
3. Population change = (births + immigration) - (deaths + emigration).
5. Population density, the number of individuals in a population found within a defined area or
volume, can affect population size. In a dense population, parasites and diseases can spread more
Chapter 5: Biodiversity, Species Interactions, and Population Control
B. No population can grow indefinitely: J-Curves and S-Curves.
1. Environmental resistance is the combination of all factors that act to limit the growth of a
population.
3. Exponential growth starts slowly but then accelerates as the population increases. It occurs when a
4. Logistic growth occurs when the growth rate decreases as the population becomes larger and nears
5. Population size may stabilize at or near the carrying capacity of its environment. The result is a
sigmoid (S-shaped) population growth curve.
1. SCIENCE FOCUS Why do California’s sea otters face an uncertain future?
a. The number of offspring, the success of predators (including humans), diseases from
parasites, and toxins are variables reducing the sea otter population.
C. Species Vary in Their Typical Life Spans
2. Survivorship Curves
D. Humans are not exempt from nature’s population controls.
2. During the 14th century, the bubonic plague killed at least 25 million people.
3. Between 1981 and 2007, AIDS killed more than 27 million people and continues to claim 2
5-1 How do species interact?
CONCEPT 5-1 Five types of interactions among species—interspecific competition, predation, parasitism,
mutualism, and commensalism—affect the resource use and population sizes of the species.
2. Describe resource partitioning, including why it occurs and its consequences. Give an example of
resource partitioning.
4. Explain how species interactions alter populations and influence natural selection, specifically co-
evolution.
5-2 How do communities and ecosystems respond to changing environmental conditions?
CONCEPT 5-2 The species composition of a community or ecosystem can change in response to changing
environmental conditions through a process called ecological succession.
1. Define birth rate, death rate, immigration, and emigration. Write an equation to mathematically
describe the relationship between these rates and the rate of population change. How do reproductive
patterns influence population size?
2. Define limiting factor. Give an example of a resource that could be limiting in an ecosystem.
4. Describe two different reproductive strategies and give an example for each strategy.
6. Compare a J-shaped growth curve to an S-shaped growth curve and comment on the factors that
produce the sigmoid (S-shaped) curve.
7. Define environmental resistance and carrying capacity and explain what determines the carrying
8. What is a population crash and when is a population likely to experience one? Describe two
5-3 What limits the growth of populations?
CONCEPT 5-3 No population can grow indefinitely because of limitations on resources and because of
competition among species for those resources.
2. Define climax community. Describe the traditional and current views of succession.
3. Describe two characteristics of living systems that provide some degree of stability.
Key Terms
age structure
carrying capacity
coevolution
competition
parasitism
persistence (inertia)
population
population crash
range of tolerance
resilience
resource partitioning
scientific principles of
Teaching Tips
Because population sizes have an impact on sustainability, try to demonstrate what changes in population
size means to resource competition.
• Ask students how many people they share their household with and what type of competition
issues arise. When the groceries are unpacked, does anyone take more than their share of
anything? Is there competition over certain food items, such as ice cream or other treats?
Use a specific species like the sea otter or a local bird to relate the biodiversity, species interactions, and
population control concepts.
• Once you have discussed a specific species with its characteristics, try to list all the other species
Discussion Topics
1. Select a species to research then specify its niche, its relationships with other species, and what
adaptations allow it to be successful. If the species is threatened or endangered, discuss the reasons
why.
2. What are some unusual niches? Write a case study for a particular alien species, indicator species, or
3. Why are competition and predation important features of natural selection?
4. How do species successfully coexist in natural ecosystems?
5. What influences the growth of a specific species? Humans?
6. What are the issues challenging the California sea otter population? Why is this particular population
being studied? What other populations should be studied? What criteria should be used in determining
what populations to study?
7. How do humans influence succession? Compare and contrast primary and secondary ecological
8. What changes in environmental conditions alter the composition of species and their population sizes?
9. To what extent should we disrupt and simplify natural ecosystems for our food, clothing, shelter, and
energy needs and wants?
10. Do predators fulfill a valuable ecological function or should their numbers be reduced?
Activities and Projects
1. Arrange a field trip that provides opportunities to compare and contrast ecosystems of several different
types, including some damaged or stressed by human activities. Invite an ecologist or biologist along
to identify and discuss specific examples of species adaptation to environmental conditions. Do the
boundaries between different kinds of ecosystems tend to be sharply delineated? Can you identify
factors that limit the growth of certain species?
2. Organize a class field trip to systematically investigate the ecological niches for plant and animal life
4. Organize a class trip to a natural area such as a forest, grassland, or estuary to observe a variety of
species interactions. Arrange for an ecologist or a naturalist to provide interpretive services.
5. Organize a class trip to an abandoned field, coastal dune, rock outcrop, or other disturbed area and
6. Invite a local state or county wildlife management professional to visit your class and discuss strategies
for handling fires in natural ecosystems. How have the policies of the U.S. Park Service changes in the
last 20 years? 50 years? Is Smokey the Bear still valid?
Instructor’s Manual for Environmental Science, 15th edition
Attitudes and Values Assessment
1. Do you have any particular feelings about relationships demonstrated in ecosystems? Competition?
Predation? Commensalism? Parasitism? Mutualism?
2. Have you ever suffered from environmental stress? If so, how did you respond to the stress? Please
3. Is there evidence of environmental stress in your community?
4. Is there evidence of ecosystem responses to stress in your community?
5. How do you feel when you see an ecosystem under stress?
6. Do you feel you have a right to create environmental stress? Are there limits to your rights? If so, what
are they?
7. Do you feel you have a responsibility to protect natural ecosystems?
8. Has your local ecosystem been invaded by a nonnative species? If so, how did you feel about the
invasion?
9. What role should humans play in increasing or decreasing population sizes of other species?
Laboratory Skills
Wells, Edward. Lab Manual for Environmental Science. 2009. Lab #4: Biomagnification Through a Food
Chain.
News Videos
Chapter 5: Biodiversity, Species Interactions, and Population Control
Additional Videos
Web Resources
Hare and Lynx Populations
A complete lesson plan exploring the classic population control model.
http://www.mysciencebox.org/book/export/html/81
Digital Integration
Correlation to Global Environment Watch
Carrying Capacity Limits to Growth
Correlation to Virtual Field Trips
Keystone Species
Correlation to Explore More
Biomes Ecology
Suggested Answers to End of Chapter Questions
Answers will vary but these represent phrases from this chapter. The following are examples of the material
Review
Core Case Study
1. Explain how southern sea otters act as a keystone species in their environment. Explain why we
should care about protecting this species from premature extinction, which could result primarily from
human activities.
Instructor’s Manual for Environmental Science, 15th edition
Section 5-1
2. What is the key concept for this section? Define and give an example of competition, and distinguish
between interspecific and intraspecific competition. Define and give an example of resource
partitioning and explain how it can increase species diversity. Define predation and distinguish
between a predator species and a prey species and give an example of each. What is a predator–prey
relationship and why is it important?
• CONCEPT 5-1 Five types of interactions among species—interspecific competition, predation,
parasitism, mutualism, and commensalism—affect the resource use and population sizes of the
species in an ecosystem.
• Interspecific competition occurs when members of two or more species interact to gain access to
the same limited resources such as food, water, light, and space. An example is moss and lichen
competing for surfaces to grow on.
3. Explain why we should preserve kelp forests. Describe three ways in which predators can increase
their chances of feeding on their prey and three ways in which prey species can avoid their predators.
Define and give an example of coevolution.
• Kelp forests are one of the most biologically diverse ecosystems found in marine waters,
supporting large numbers of marine plants and animals. (Science Focus). Kelp forests help reduce
shore erosion. Kelp contains a substance that is an ingredient in toothpaste, cosmetics, ice cream,
and hundreds of other products.
4. Define parasitism, mutualism, and commensalism and give an example of each. Explain how each of
these species interactions, along with predation, can affect the population sizes of species in
ecosystems.
• Parasitism occurs when one organism (the parasite) feeds on another organism (the host), usually
by living on or in the host. In parasitism, the parasite benefits and the host is harmed. Examples
include a tick on a deer and tapeworms inside dogs.
Section 5-2
5. What is the key concept for this section? What is ecological succession? Distinguish between primary
ecological succession and secondary ecological succession and give an example of each.
• CONCEPT 5.2 The species composition of a community or ecosystem can change in
response to changing environmental conditions through a process called ecological
succession.
6. Explain how living systems achieve some degree of sustainability by undergoing constant change in
response to changing environmental conditions. In terms of the stability of ecosystems, distinguish
between inertia (persistence) and resilience and give an example of each.
7. What is the key concept for this section? Define population. Why do most populations live in clumps?
List four variables that govern changes in population size. Write an equation showing how these
variables interact. What is a population’s age structure and what are the three major age groups called?
Instructor’s Manual for Environmental Science, 15th edition
Define range of tolerance. Define limiting factor and give an example. Define population density and
explain how some limiting factors can become more important as a population’s density increases.
Define and give an example of a population crash. Explain why humans are not exempt from nature’s
population controls.
CONCEPT 5-3 No population can continue to grow indefinitely because of limitations on resources
and because of competition among species for those resources.
• A population is a group of individuals of the same species living in a particular place.
• The four variables that govern changes in population size are: births, deaths, immigration, and
emigration. A population increases by birth and immigration (arrival of individuals from outside
8. Distinguish between the exponential and logistic growth of a population and describe the nature of
their growth curves. Define environmental resistance. What is the carrying capacity of an
environment? Define and give an example of a population crash.
• Species with exponential population growth typically reproduce at an early age, have many
offspring each time they reproduce, and reproduce many times, with short intervals between
successive generations.
9. Describe two different reproductive strategies for species. Distinguish between r-selected species and
K-selected species and give an example of each. Define survivorship curve and describe three types
of curves. Why is the recovery of the southern sea otters slow and what factors are threatening this
recovery? Explain why humans are not exempt from nature’s population controls.
• Species that have a capacity for a high rate of population increase (r) are called r-selected species.
They tend to have short life spans and to have many, usually small, offspring - most insects.
Chapter 5: Biodiversity, Species Interactions, and Population Control
• Reasons the southern sea otter population is not rapidly increasing include.
o The southern sea otter has a low reproductive rate, reaching sexual maturity between 2
and 5 years of age and typically producing only one pup a year
10. What are this chapter’s three big ideas? Explain how the interactions of plant and animal species in
any ecosystem are related to the three principles of sustainability.
• This chapter’s three big ideas are:
o Certain interactions among species affect their use of resources and their population
sizes.
Critical Thinking
1. What difference would it make if the southern sea otter (Core Case Study) became prematurely extinct
because of human activities? What are three things we could do to help prevent the extinction of this
species?
The extinction of the sea otter would cause drastic changes in the kelp forest communities, as they are
a keystone species, controlling sea urchin populations that would otherwise decimate the highly
2. Use the second law of thermodynamics and the concept of food chains and food webs to explain why
predators are generally less abundant than their prey.
Predators are at higher trophic levels than their prey. There is less energy and biomass when going
3. How would you reply to someone who argues that we should not worry about the effects that human
activities have on natural systems because ecological succession will repair whatever damage we do?
` Environmental damage to natural ecosystems can take various forms. In the case of land that has been
farmed or logged and then abandoned, new species will begin to take over the land through secondary
succession. But for the original plants (the climax community) to reach an equilibrium, it could take a
do need to worry about human effects on natural systems.
4. How would you reply to someone who contends that efforts to preserve species and ecosystems are not
worthwhile because nature is largely unpredictable?
Answers will greatly vary and should help students understand different perspectives. The greater the
5. Explain why most species with a high capacity for population growth (such as bacteria, flies, and
cockroaches)tend to have small individuals, while those with a low capacity for population growth
(such as humans, elephants, and whales) tend to have large individuals.
Species with a high capacity for population growth tend to be born small and have minimal time and
6. Which reproductive strategy do most species of insect pests and harmful bacteria use? Why does this
make it difficult for us to control their populations?
7. List two factors that may limit human population growth in the future. Do you think that we are close
to reaching those limits? Explain.
In the past, human populations have been limited by disease, food productivity, and the type of habitat
8. If the human species were to suffer a population crash, what are three species that might move in to
occupy part of our ecological niche?
Chapter 5: Biodiversity, Species Interactions, and Population Control
Global Environment Watch Exercise
Search for kelp forests (also sometimes called kelp beds), and use the results to find sources of information
about how a warmer ocean, as a result of climate change, might affect California’s coastal kelp forests on
which the southern sea otters depend (Core Case Study). Write a report on what you found. Try to
include information on current effects of warmer water on the kelp beds as well as projections about future
effects. Also, summarize any information you might find on possible ways to prevent harm to these kelp
forests.
Using the graph showing changes in the size of an Emperor penguin population in terms of numbers of
breeding pairs on the island of Terre Adelie in the Antarctic, answer the following questions.
1. Assuming that the penguin population fluctuates around the carrying capacity, what was the
approximate carrying capacity of the island for the penguin population from 1960 to 1975? What was
the approximate carrying capacity of the island for the penguin population from 1980 to 2010?
2. What was the overall percentage decline in the penguin population from 1975 to 2010?
3. What is the projected overall percentage decline in the penguin population between 2010 and 2100?
