Download Chapter 57 Instructor Manual

CHAPTER 57: Dynamics of Ecosystems
WHERE DOES IT ALL FIT IN?
Chapter 57 builds on the foundations of biodiversity and provides detailed information about
environmental interactions of organisms. Students should be encouraged to recall the principles of
organismic classification and comparative anatomy. The information in chapter 57 does not stand
alone. It connects the information on organismic diversity to evolution and ecology coverage.
Students should know that animals and other organisms are interrelated and originated from a
common ancestor of all living creatures on Earth.
SYNOPSIS
Ecosystems follow biological communities in the increasingly complexity toward the biosphere.
Ecosystems are the most complex level of organization because they include biotic and abiotic
factors. The Earth is a closed system with respect to chemicals and nutrients, but an open system
with regard to energy from the sun. All substances in organisms cycle through the ecosystem.
These cycles may be short lived or may take thousands of years to go full circle. Many of these
substances have atmospheric reservoirs while others are contained within soils and rocks. Rarely
is the bulk of any substance contained within bodies of organisms. However, one must consider
the tremendous amounts of stored nutrients (for example carbon, oxygen, nitrogen) that are
stored in plant tissues in a forest or grassland. Among the more important biogeochemical cycles
are those that involve water, carbon, nitrogen, and phosphorus.
Life depends on water, 98% of which is found in oceans, in surface fresh water, and as ground
water. Life also depends on carbon, most of which is contained in the carbon dioxide of the
atmosphere. Various photosynthesizers fix carbon into organic substances which are then passed
to various heterotrophs. Carbon is returned to the atmosphere via respiration and when an
organism dies and decomposes. Until recently, the processes of photosynthesis and
respiration/decomposition have roughly balanced each other. The burning of fossil fuels (coal,
oil, natural gas) and the destruction of vast areas of photosynthesizing plants is tipping that scale
in the direction of increased atmospheric carbon dioxide. Nitrogen gas comprises 78% of the
atmosphere. It is only available to organisms by the action of various nitrogen-fixing bacteria.
Leguminous plants harbor such bacteria, which are readily visible in their root nodules. They fix
sufficient nitrogen for their own growth and release the excess into the soil, fertilizing it without
the addition of costly chemicals. The phosphorus cycle is typical of many of the other mineraloriented biogeochemical cycles. Much phosphorus is taken up by marine organisms which are
then eaten by ocean birds. Guano is among the richest fertilizers available.
Only a small percentage of the sun’s energy is captured by photosynthesizers; even less of this
energy is passed on to animals. In terms of energy utilization, it is better to be a vegetarian or
herbivore than a carnivore. Each successive level of consumer is a trophic level and includes
photosynthesizers, primary consumers, secondary consumers, decomposers, and detrivores.
Primary productivity is the total amount of organic matter produced from the sun’s energy within
a given system. Some energy is lost in the metabolic activities of the initial photosynthesizers,
resulting in the net primary productivity value. The weight of all of the organisms living in an
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ecosystem is the biomass of that ecosystem. This figure increases as a result of net productivity.
Many ecosystems have both high productivity and high biomass. Others have high productivity
but low biomass. Tropical forests and wetlands have the highest biomass ratios, while deserts
have the lowest. Energy is passed through an ecosystem in a series of small steps comprising a
food chain or a food web. In theory, higher productivity should support longer food chains, but
in reality little energy remains after only four steps. The relationships of these trophic levels are
diagrammatically represented by biomass and energy pyramids. Occasionally a biomass pyramid
may be inverted, but the energy pyramid cannot be inverted. Trophic levels dramatically affect
each other through a phenomenon called a trophic cascade. Lower trophic levels can influence
higher levels via bottom-up effects. In addition lower and higher trophic levels can cancel each
other out or reinforce each other, producing extremely complicated food web interactions.
Biodiversity, species richness, and species diversity promote community stability. Factors that
promote species richness include ecosystem productivity, spatial heterogeneity, and climate. The
tropics exhibit a greater number of species than any other biome. This may be due to the long
evolutionary age of the tropics combined with high productivity, predictability of climate,
intense predation, and spatial heterogeneity. A predictable species-area relationship has been
observed as one of the most predictable patterns in ecology. The equilibrium model of island
biogeography proposes that, in time, the number of species extinctions and colonizations balance
each other out and the number of species remains constant. In addition, distance to sources (other
islands or to a mainland) for colonizers and island size play important roles in supporting the
colonization/extinction events that occur on islands. Islands should not just be though of as
“somewhere” in the Pacific Ocean but also mountain tops and other isolated areas on the planet.
LEARNING OUTCOMES
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Understand the nature of an ecosystem.
Discuss the five primary biogeochemical cycles, including the reservoirs and unique
organisms upon which each cycle depends.
Explain the difference in nutrient cycling and energy flowing through an ecosystem.
Discuss the effects of deforestation on the water cycle, flood control, and overall fertility.
Understand the relationship of one trophic level with another in terms of energy and biomass.
Differentiate between gross and net productivity and explain how each is related to biomass.
Compare the overall productivity of each of the major ecosystems to one another.
Explain why algal beds and coral reefs have a larger NPP per unit area than do tropical rain
forests.
Identify the components of a general food chain. With the exception of deep ocean vents,
explain why an autotroph is absolutely required to be in the first “trophic link” in a food
chain.
Explain what an ecological pyramid is and what different shapes indicate.
Understand how trophic cascades and bottom-up effects influence populations at other
trophic levels and how the two effects interact.
Compare species richness and species diversity and the factors that promote each.
Understand the importance of the equilibrium model in island biogeography.
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Be able to explain the graphs that are used to illustrate the island biogeography mode
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 57 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students are unaware of the low of energy through trophic levels
Students are unable to track the path of carbon through an ecosystem
Students are unable to track the path of nitrogen through an ecosystem
Students are unable to track the path of phosphorus through an ecosystem
Students are unable to track the path of sulfur through an ecosystem
Students are unaware of the concept of limiting factor
Students are unaware of the complexity of organismic interactions
Students believe that predator-prey population fluctuations are uniform over time
Students do not account that predators seek many types prey when looking at population
fluctuations
Students do not account that prey are taken by several types of predators when looking at
population fluctuations
Students are unaware of evolution at the population level
Student think that selection is directional and produces superior characteristics
Students believe that most animals are vertebrates
Students believe that most plants are angiosperms
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
It is most valuable to present the cyclic nature of biogeochemical cycles, their reservoirs, and
how they are affected by organisms.
Use index cards with the various trophic levels printed on one side—for example, producer, first
level consumer. Pass the cards out randomly at the beginning of class. Then request that food
chains and webs forms. Then disrupt the chains. For example, remove the consumers or the
decomposers. This activity should allow students to connect the idea of the important role that
each member plays within a food chain or web.
Explain the “Nitrogen Paradox.” There is an abundance of nitrogen in the atmosphere but the
majority of life forms cannot use any of it, despite the importance of nitrogen atoms in amino
acids and nucleotides. You can lead students through this with some prodding.
This is another appropriate location to discuss the greenhouse effect as it relates to the carbon
cycle. Photosynthesis and respiration should be in balance. When forests are destroyed,
photosynthesis decreases. Carbon dioxide increases if forests are burned or if trees decompose
naturally. The ultimate result is increased atmospheric carbon dioxide, which traps heat in the
atmosphere causing increasing global temperatures (an excellent example of positive feedback).
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Have students conduct an energy assessment of what they use on a daily basis. Keep this for 24
hours, submit to instructor, tabulate results and demonstrate how just the members of that
particular biology class impact the planet. For example, light on in bedroom for 2 hours, radio on
all day, shower lasted 10 minutes. Students will be amazed with the data.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 57.
Application
Analysis
Synthesis
Evaluation
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Have students explain the role of autotrophs in an ecosystem.
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Have students explain the role of decomposers in a pond ecosystem.
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Ask students to trace the path of a carbon atom through an ecosystem.
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Have students explain impact of elevated carbon dioxide levels on a forest
ecosystem.
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Have student describe the effects of fertilizing a yard on the
biogeochemical pathways on nearby wilderness areas.
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Ask students to explain the value of reducing the amount of nitrogen
fertilizer that leaks into an aquatic ecosystem.
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Ask students to design to test the impacts of pet cats on local bird
populations.
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Have students come up with an agricultural application of the knowledge
that nitrogen is used for amino acid synthesis in plants.
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Ask the students come up an experiment to test if species richness is
improved by environmental preservation projects.
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Ask students evaluate the use of introducing small predatory animals to
control rat populations in suburban areas.
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Ask students to assess a law that bans the planting of certain imported
trees in suburban yards.
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Ask students investigate the pros and cons of planting young trees to
replace those removed for paper and lumber production.
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VISUAL RESOURCES
Bring in photos of organisms that exemplify various kinds of trophic levels and/or food webs.
Bring current graphs that show the evidence for increasing global temperatures, increasing levels
of atmospheric carbon dioxide and decreasing levels of forested areas across the world. Let
students see the cause and effect relationship.
Bring photos of wind turbines and solar farms to generate discussion of alternate energy sources
for the planet. What are their benefits? What are their liabilities?
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Computer Modeling of Ecosystems
Introduction
This demonstration has students assess the use and importance of computer models for
understanding environmental changes that affect populations.
Materials
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Computer with Media Player and Internet access
LCD hooked up to computer
Web browser linked to Oak Ridge National Laboratory website at
http://www.ornl.gov/sci/gist/
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Procedure & Inquiry
1. Tell the class the ecologists today use computer and mathematical modeling to better
understand ecosystem dynamics.
2. Load up the Oak Ridge National Laboratory website and click on the Projects bar
3. Select 3-D Visualization tab from the main window
4. Go through the two animations (give time for the animations to completely download
before running)
5. Have students describe what they see in each animation.
6. Ask the students to think about the type of information that can be collected from the
visualizations.
USEFUL INTERNET RESOURCES
1. The United States Environmental Protection Agency Global Climate Change website has
various types of information for discussing the possible impacts of global climate change
on the dynamics of various ecosystems. The site is available at
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http://www.epa.gov/climatechange/.
2. The USDA Forest Service has an informative website with information about the impacts
of human activity on local ecosystems. It also has many images that can be used in
teaching ecosystem concepts. This website can be found at http://www.fs.fed.us/.
3. The Department of Agriculture's (USDA) Animal and Plant Health Inspection Service
(APHIS) website has valuable classroom information about the impacts of invasive
organisms on natural and urban environments. The website can be found at
http://www.aphis.usda.gov/.
4. Case studies are an effective tool for stimulating interest in a lesson on animals. The
University of Buffalo has a case study called “Salton, A Sea of Controversy” which has
students investigating ecosystem dynamics. The case study can be found at
http://www.sciencecases.org/salton/salton.pdf.
LABORATORY IDEAS
A. Using Databases to Study Ecosystem Dynamics
This activity has students use databases to study ecosystem dynamics in the Baltic Sea.
a. Explain that students will be using real environmental databases to investigate the
possibility of ecosystem changes in the Baltic Sea. They are to use the data to determine
change and then try to explain the factors that caused any measurable changes.
b. Provide the students with the following:
a. Computers with Internet Access
b. Web browser bookmarked to The Baltic Sea Portal Website at:
c. http://www.fimr.fi/en/itamerikanta.html
c. Tell students to explore The Baltic Sea Portal website and familiarize themselves with the
environmental characteristics of the Baltic Sea.
d. Then direct the students to go to the Baltic Sea Now link.
a. Ask the students to see if there were any algal population fluctuations in the
measurements provided in the database.
b. Direct them to learn about the algae by following the Algae Information link.
e. Have the students use the environmental measurements to see if algal populations
fluctuated with any of the measurements such as salinity, temperature, and turbidity.
f. Students should be asked to present a report supporting their observations and
conclusions. Conclusions should be backed by citing previous research studies about
variables that affect algal growth.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
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Have students volunteer at a nature center.
Have students tutor high school students studying ecology.
Have students do a presentation on biodiversity to elementary school students.
Have students volunteer with a conservation group on biodiversity preservation projects
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