Three-dimensional Learning Progression This Lesson includes three activities in which students begin to analyze ecosystems as systems that are constantly transforming matter and energy rather than as collections of plants and animals in a particular setting. Key Ideas and Practices for Each Activity In Activity 2.1 students make the transition from a picture of a meadow as a place where plants and animals live to a more abstract representation of the organic mass of populations of producers, herbivores, and carnivores in an ecosystem and make predictions about mass of each group in a meadow. In Activity 2.2 students use an online simulation to investigate the relative sizes of the organic mass of populations of producers, herbivores, and carnivores and how they change over time. The Meadow Simulation allows students to run multiple scenarios adjusting initial populations of grasses, rabbits, and foxes to observe changes in the mass of the populations over a 100-year period. Through the online simulations students will need to notice two patterns: 1) the mass of the populations of producers, herbivores, and carnivores changes over time and 2) over time a consistent pattern emerges: The mass in the rabbit population is smaller than the grass biomass, and mass in the fox population is always the smallest. Different initial mass of grasses, rabbits and foxes lead to different patterns of change, but the foxes can survive only if the grass mass stays large. In Activity 2.3 students complete the Evidence-Based Arguments Tool for the patterns of change in carbon pools that they observed in the Meadow Simulation. In addition to describing the pattern that they have observed—the organic matter pyramid—they formulate questions about why that pattern emerges for many different original settings. They will answer these questions in Lesson 3. In Activity 2.4, students are introduced to the amount of organic carbon in different ecosystems. They observe the same pattern in producers, herbivores, and carnivores in four different types of ecosystems that have different amounts of total organic matter. They also see that in most terrestrial ecosystems, the largest organic matter pool is soil carbon. (Ecologists would say that the organic matter pyramid should more accurately be applied to production—the rate of biosynthesis at each trophic level—rather than biomass. There are aquatic ecosystems where the producers—phytoplankton—grow very fast and are eaten very fast, so there is more mass stored in consumers. This is not an important point for this Unit.) Content Boundaries and Extensions
