46
Ecosystems
Chapter Outline
Ecosystems
46.1 too much of a good thing
46.2 The Nature of Ecosystems
Overview of the Participants
Trophic Structure of Ecosystems
46.3 The Nature of Food Webs
How Many Transfers?
46.4 Energy Flow
Primary Production
Ecological Pyramids
Ecological Efficiency
46.5 Biogeochemical Cycles
46.6 The Water Cycle
How and Where Water Moves
Limited Fresh Water
46.7 the Carbon Cycle
Terrestrial Carbon Cycle
Marine Carbon Cycle
Carbon in Fossil Fuels
46.8 Greenhouse Gases and Climate Change
The Greenhouse Effect
Changing Carbon Dioxide Concentrations
Changing Climate
46.9 Nitrogen Cycle
Reactions That Drive the Cycle
Human Effects on the Cycle
Nitrous Oxide
Nitrates
46.10 The Phosphorus Cycle
too much of a good thing(REVISITED)
summary
self-quiz
data analysis activities
critical thinking
Ecosystems
Learning Objectives
46.1 Illustrate eutrophication using an example.
46.2 Examine the trophic structure of ecosystems.
46.3 Describe the different trophic levels with examples for each level.
46.4 Determine how energy flows from primary producers to other trophic levels.
46.5 Illustrate the biogeochemical cycle using a diagram.
46.6 Illustrate the water cycle using a diagram.
46.7 Demonstrate the carbon cycle using a diagram.
46.8 Discuss how a change in carbon dioxide concentration changes the climate.
46.9 Examine the nitrogen cycle on land using a diagram.
46.10 Outline the role of human activities in the disruption of the nitrogen cycle.
46.11 Examine the significance of the phosphorus cycle in the ecosystem.
Key Terms
Ecosystems
ammonification
aquifer
atmospheric cycle
biogeochemical cycle
biomass pyramid
carbon cycle
consumers
decomposers
denitrification
detrital food web
detritivores
ecosystem
energy pyramid
eutrophication
food chain
food web
global climate change
grazing food web
greenhouse gas
groundwater
nitrification
nitrogen cycle
nitrogen fixation
phosphorus cycle
primary producers
primary production
runoff
sedimentary cycle
soil water
trophic levels
water cycle
watershed
Ecosystems
Lecture Outline
46.1 Too Much of a Good Thing
A. Phosphorus is a substance that is necessary for life.
1. Plants obtain phosphorus from the soil and animals get their supply from consuming
plants or other animals.
2. If the soil is depleted of phosphorus, fertilizers may be added to supplement the soil.
B. When fertilizers enter the runoff, it can cause problems in water supplies.
1. In the water of lakes and rivers, eutrophication may occur.
a. Algae blooms cause the water to become polluted and make it inhabitable for many
other organisms.
C. Now scientists are aware of the problems man has created by disrupting the nitrogen cycle.
46.2The Nature of Ecosystems
A. Overview of the Participants
1. An ecosystem is the sum of the organisms residing there and the environment.
a. A primary producer is the plant that serves as an autotroph by harnessing the sun’s
energy.
b. A consumer is the animal or heterotroph that derives energy from consuming the
plant or other animals.
c. A detritivore is an animal that consumes debris and small bits of organic matter.
d. A decomposer eats wastes and remains of plants and animals.
e. Minerals increase and decrease in natural cycles.
B. Trophic Structure of Ecosystems
1. The organisms of an ecosystem develop trophic levels or feeding relationships.
a. A food chain represents the passage of energy from one trophic level to the next.
b. Plants are the primary producers, and they represent the first trophic level.
c. The second trophic level is represented by primary consumers, animals that eat plants.
d. Secondary producers (third trophic level) consume animals at the second trophic
level.
e. Finally, the fourth trophic level (third-level consumers) consume animals from the
third trophic level.
46.3The Nature of Food Webs
A. A food web is a complex interaction among many species of the ecosystem.
1. In a grazing food chain, the energy goes from producers to consumers.
2. In a detrital food chain, the energy goes from producers to detritivores and decomposers.
B. How Many Transfers?
1. An alteration in one species of a food web may affect many different organisms.
a. Scientists have discovered how complicated food webs are, “Everything is linked to
everything else.”
46.4Energy Flow
A. Primary Production
1. Primary production is the rate at which plants harness the sun’s energy.
2. This depends on the availability of water and nutrients.
3. Primary production is higher on land than in water.
B. Ecological Pyramids
1. A biomass pyramid is used as a tool to represent the dry weight of the organisms at each
trophic level.
a. The plants or producers make up the base of the pyramid.
b. Consumers make up the upper portion of the pyramid, with the largest carnivores at
the very top.
2. An energy pyramid helps show how energy is lost when transferred to each trophic
level.
C. Ecological Efficiency
1. Only about 5–30 percent of the energy in the tissues of an organism ends up in the tissues of the next trophic level.
a. Energy is lost because some is lost as heat, and many parts of an animal cannot be
digested.
2. The energy transfer in watery ecosystems is usually more efficient than those on land.
46.5 Biogeochemical Cycles
A. In biogeochemical cycles, nutrients move through environmental stores and living organisms.
1. The elements enter the living portion of the cycle by becoming incorporated into plants.
2. Examples of biogeochemical cycles are the water, carbon, nitrogen, and phosphorus cycles.
46.6The Water Cycle
A. How and Where Water Moves
1. The water cycle begins when water evaporates from bodies of water and transpiration occurs in plants.
2. Next, water condenses in clouds and rains down.
3. Water collects in watersheds, aquifers, and groundwater.
a. Most individuals get water supply from groundwater.
b. Groundwater can be easily polluted and difficult to correct.
B. Limited Fresh Water
1.Groundwater is the major water supply for about half of the U.S.
- Salt water is replacing many coastal aquifers.
- Other areas, especially in the southwest, have depleted groundwater.
2.A future water supply may be the ocean through utilization of a desalinization process to remove the salts.
46.7 Carbon Cycle
A. Terrestrial Carbon Cycle
1. Soil, consisting of humus and soil organisms, contains much more carbon than the
atmosphere.
- In tropical areas more carbon is in living plants, whereas in the temperate zone the
majority of the carbon is in the soil.
2. Tilling the soil increases the amount of carbon in the atmosphere.
B. Marine Carbon Cycle
1. Most of the carbon is in seawater.
a. The carbon in the ocean is formed from the shells of small organisms.
b. The crust lifts up and becomes part of the land mass.
- Eventually erosion breaks down the rocks and the carbon travels back to the sea.
C. Carbon in Fossil Fuels
1. Fossil fuels are formed from decayed plants and plankton.
2. Man adversely affects the carbon cycle by releasing more carbon into the air, contributing
to global warming.
46.8Greenhouse Gases and Climate Change
A. The Greenhouse Effect
1. The sun’s heat is absorbed by the Earth’s surface.
2. Some of the heat is reflected back into the atmosphere, but atmospheric gases send some
heat back to Earth.
3.The greenhouse effect is a natural, necessary phenomenon to maintain reasonable
temperatures on Earth.
B. Changing Carbon Dioxide Concentrations
1. When scientists began to measure carbon dioxide levels in 1959, they saw annual fluctuations.
a. The carbon dioxide levels drop in the summer when plants use it for active
photosynthesis.
b. The carbon dioxide levels rise in the winter when there is less photosynthesis
occurring.
2. Overall, the carbon dioxide levels in the atmosphere are rising.
a. Scientists were able to check carbon dioxide levels in the past by drilling deep into
glaciers or by examining fossil foraminiferan shells.
b. The carbon dioxide level in the atmosphere is the highest it has been in 15
million years.
C. Changing Climate
1. Currently a global climate change is occurring, which can be defined as a long-term change in the Earth’s climate.
a. Global warming is causing a warmer ocean temperature, which results in melting glaciers and more severe storms.
2. Scientists in 2007 determined that the rise in temperature was due to human activities.
b. Efforts are underway to reduce the use of fossil fuels as energy sources.
46.9 Nitrogen Cycle
A. Nitrogen exists in the atmosphere as N2,which is not in a usable form for plants.
1. Some natural processes such as lightening and volcanoes can convert the nitrogen to a usable form.
2. The bacteriarhizobium that exists in nodules on legumes also converts the nitrogen to a usable form.
3. Plants obtain ammonium from the soil,which is later broken down by fungi and bacteria in a process called ammonification.
4. Nitrification is the process that converts ammonium to nitrates.
a. First, ammonia is converted to nitrite by bacteria and archaea.
b. Then other types of bacteria change nitrites into nitrates.
c. Nitrates and ammonium are used by producers.
5. Denitrification is the process in which bacteria convert nitrate to nitrogen gas in the atmosphere.
B. Human Effects on the Cycle
1. Nitrous Oxide—A Double Threat
a. From testing the nitrous oxide level in ice core, scientists have seen the level rise from 270 ppb to 325 ppb.
b. Increases in nitrous oxide are due to commercial fertilizers, livestock production, and the burning of fossil fuels.
2. Increased amounts of nitrous oxide in the atmosphere can lead to global warming and depletion of the ozone layer.
C. Nitrate Pollution
1. Nitrates are common contaminants in the water supply.
a. They may result from fertilizer use or septic tank malfunctions.
2. Nitrates have been known to increase the risk of thyroid cancer, respiratory infections, diabetes, and other cancers.
3. The EPA has said that drinking water should contain no more than 10ppm of nitrate.
a. Usually private wells go untested.
46.10The Phosphorus Cycle
A. Phosphorus cycles between the land and the ocean.
1. Phosphates are necessary for major cellular components like nucleic acids, plasma membranes, and ATP.
2. Plants get phosphorus from the water and soil, and animals get it from consuming plants or other animals.
a. Phosphorus levels are quite often a limiting factor for plant growth.
b. A lack of phosphorus in the soil can be due to the absence of crop rotation.
B. An excess of phosphorus can result from water that runs off from fertilized fields.
1. Excessive amounts of phosphorus in a watery environment can cause eutrophication.
a. An algae bloom occurs that harms other plant and animal species.
b. Eutrophication is difficult to reverse.
46.12 Too Much of a Good Thing (Revisited)
- Fertilizers are used heavily in agricultural areas to improve crop yields.
- This causes excess nitrogen and phosphates to enter water supplies through runoff.
- These increases enter the Mississippi River and ultimately flow into the Gulf of Mexico.
- These excess nutrients produce a “dead zone” in the Gulf of Mexico.
- Eutrophication causes low oxygen levels and, therefore, causes the death of many organisms.
Suggestions for Presenting the Material
•Approach the study of the various cycles of an ecosystem by first explaining the necessity of that particular component in the environment. Then examine the deleterious effects of too little or too much of that substance.
•Begin by showing a simple food chain and an example of a representative animal at each trophic phase. Then stress that life and nature are rarely that basic. Show the students an example of a complex food web and discuss the unlikelihoodthat an animal would have only one food source. Create a disruption in the food web by imagining the destruction of a population of one species of animal. Let the students see that a seemingly small changein a food web could have a dramatic impact on many other species. Students will become aware of the unity that joins all organisms.
•Have the students view the award-winning documentary “An Inconvenient Truth.” This powerful film may help to launch a discussion of the consequences of global warming and the impact that this movie has created worldwide.
•Use as many local examples of ecosystems as possible in discussions, demonstrations, and lab work. While it may seem overly simplistic and sometimes inaccurate to identify and describe the different levels of an ecosystem, students should see that it is useful because it helps us to understandthe functioning of an ecosystem as a whole. Such ecosystem descriptions provide a valuable baseline against which we can measure the effects of changes.
•Stress the fact that, in various sections of the chapter, the authors show how humans have altered the natural ecosystems and their functioning.
•Use overhead transparencies to present the biogeochemical cycles.
•Invite a representative of the EPA, the state coastal commission, or another environmental group to address the class.
•Have students build their own food web using the online resource:
- Go around the room and have the students name examples of producers, consumers, detritivores, and decomposers that would be in the area surrounding your campus.
- See if your students can devise a food chain (or better yet, a food web) for organisms in your area. This will serve to show them how complicated and intertwined these relationships are.
Classroom and Laboratory Enrichment
•Have some of the students choose a cycle discussed in this chapter and make a poster depicting the stages. Each participant should explain his poster to the class and how human intervention may alter the natural cycle.
•Set up aquatic ecosystems in the lab and monitor them throughout the semester. Identify the trophic levels of the ecosystem and analyze the cycling of materials and nutrients within it. In what ways are the aquatic ecosystems in the lab similar to, or different from, a real aquatic ecosystem?
•Discuss the primary productivities of different regions of the United States. How can human intervention change primary productivity?
•Each student could undertake a study near their home of an environmental issue regarding an upset of one of the natural biogeochemical cycles.Are there any reasonable solutions to this issue? If so, write to your senator or congressman expressing your views.
•Test various water supplies for the presence of nitrogen and phosphorus. Are they within the recommended standards? If not, how far do they deviatefrom a normal level? Use a nursing or anatomy text to determineif an excess of either substance would cause any short-term or long-lasting effects?
•Determine the pH of water samples from several local bodies of water in your area. How much does the pH vary? If you have suitable equipment at your school, you can use a Global Positioning System to create maps of exactly where you obtained your samples. Since you are somewhat familiar with the area, can you find a reason to explain these differences in pH?
•Fill an aquarium with water and organisms from a nearby pond or lake. Add amounts of phosphorus and nitrogen to mimic eutrophication. What effects do you see in your artificial ecosystem?
•Analyze local soils to determine the mineral and organic contents.
•Divide the class into small groups. Have each section debate the pros and cons of different energy sources. Each group should be prepared to discuss the merits and drawbacks of one of the following energy sources: oil, coal, natural gas, hydropower, solar power, nuclear power,or other alternatives. Can the class come to any consensus about the safest method or combination of methods?
•Assuming that a flat 10 percent of the energy in one trophic level is conserved to the next, and that the producer represents 100 percent, calculate what percent is received by the marsh hawk in Figure 46.4.
•Write down the models of cars driven by some of your classmates. Research online to see if you can determine the emissions from each of these models. When you announce the results to the class, will that influence anyone’s choice for their next vehicle?
•Visit a sewage treatment plant. Discuss the biological steps involved in the treatment of your local sewage. In what way could sewage treatment be improved?
•Research the steps that will be undertaken to convert the astronauts’ urine into drinkable water in space.
•Collect some soil from what appears to be a detrital food web in a forest or field system. Can you identify any organisms as decomposers and detritivores? Do you imagine that some of the organisms performing these duties may be too small to see?
•Contact the epidemiologist at your local hospital. Inquire how they handle their dangerous biomedical wastes. In the past it was sufficient for a hospital to simply contract with a company to dispose of hazardous wastes. Now hospitals are required know the pathway of the dangerous trash after it leaves the building. This makes it clear that all parties involved are responsible for proper environmental procedures.