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Ecosystems | Lesson 4 - Ecosystem Services and Changes in the Environment

Lesson 4: Ecosystem Services and Changes in the Environment

Students discuss how humans fit into the biomass pyramid using a farm ecosystem as a model, and then read about how carbon pools change size over time.

Guiding Question

How are humans part of ecosystems?

Activities in this Lesson

  • Activity 4.1: Farms are Ecosystems, Too (30 min)
  • Activity 4.2: Changes in Ecosystems Over Time (40 min)
  • Activity 4.3: Ecosystem Disturbances (40 min)

Objectives

  1. Explain the implications for resource use of humans eating meat or plant products: The same producers can support more humans as herbivores than as carnivores.
  2. Predict and explain the effects of seasonal cycles and disturbances such as drought or fire on ecological matter cycling and energy flow.

NGSS Performance Expectations

Middle School

  • Matter and Energy in Organisms and Ecosystems. MS-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.
  • Interdependent Relationships in Ecosystems. MS-LS2-2. Construct an explanation that predicts patterns of interactions among organisms across multiple ecosystems.
  • Matter and Energy in Organisms and Ecosystems. MS-LS2-3. Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem.
  • Matter and Energy in Organisms and Ecosystems. MS-LS2-4. Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
  • Matter and Energy in Organisms and Ecosystems. MS-LS1-6. Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy in and out of organisms.
  • Human Impacts. ESS3-4. Construct an argument supported by evidence for how increases in human population and per-capita consumption of natural resources impact Earth’s systems.

High School

  • Interdependent Relationships in Ecosystems. HS-LS2-1. Use mathematical and or computational representations to support explanations of factors that affect carrying capacity of ecosystems and different scales.
  • Matter and Energy in Organisms and Ecosystems. HS-LS2-4. Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
  • Matter and Energy in Organisms and Ecosystems. HS-LS2-5: Develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere.
  • Earth’s Systems. HS-ESS2-6. Develop a quantitative model to describe the cycling of carbon among the hydrosphere, atmosphere, geosphere, and biosphere.

Background Information

In Lesson 3 students learned how the carbon-transforming processes of individual organisms led to predictable patterns in most ecosystems: matter cycling, energy flow, and the biomass pyramid. But ecosystems aren’t actually in steady states—the size of their pools change over time.

In Activity 4.1 students analyze a farm as an ecosystem. Like most ecosystems on Earth today, farms are managed by humans to produce materials that we want—in the case of the farm, food for humans. Since humans are omnivores, we can decide where we will be located in the biomass pyramid. We can choose to eat plant matter—grains, fruits, and vegetables—from the farm, or we can feed the plant matter to animals, then eat the animals. By tracing carbon atoms through organic matter pools for these two different scenarios, students can recognize how our dietary choices affect the amount of farmland needed to support humans.

Activities 4.2 and 4.3 focus on the relationships between carbon fluxes and the size of carbon pools. Fluxes are the rate at which carbon moves from one pool to another. In order analyze how changes in fluxes affect the sizes of pools we simplify the number of pools to two—organic carbon in living organisms and soil carbon and inorganic carbon in the atmosphere, and the number of carbon transforming processes to two—photosynthesis and cellular respiration.

In Activity 4.2 students investigate the relationships between pools and fluxes in four different scenarios:

  • A steady state scenario where rates of photosynthesis and cellular respiration are balanced, so the organic matter pool and the atmospheric CO2 pool are stable
  • A seasonal variation scenario where the rate of photosynthesis varies greatly between summer and winter, while the rate of cellular respiration varies less. Thus cellular respiration slows down during the winter, but it becomes the dominant process because photosynthesis slows down even more. This pattern affects seasonal CO2 concentrations on a global scale (see http://en.wikipedia.org/wiki/Keeling_Curve and the Human Energy Systems unit).
  • A planting new trees scenario where the rate of photosynthesis is consistently higher than the rate of cellular respiration, leading to a net increase in organic carbon and decrease in CO2
  • A drought scenario where the rate of photosynthesis drops consistently below the rate of cellular respiration, leading to a net increase in CO2 and a net decrease in organic carbon.

Activity 4.3 focuses on another kind of disturbance that can be caused by humans or natural events such as lightning—fire. Another carbon-transforming process—combustion—leads to a large one-time flux of carbon into the atmosphere, followed by the gradual movement of carbon back into organic carbon. A reading accompanying this lesson helps students to consider why fire is not always a bad thing, and a buildup of organic carbon in an ecosystem is not always a good thing.