Skip to Content

Ecosystems | Lesson 2 - Patterns in Biomass in Ecosystems

Lesson 2: Patterns in Biomass in Ecosystems

Students are introduced to biomass, use a simulation of a meadow ecosystem to view changes in the biomass of populations of a producer, herbivore, and carnivore under different conditions, and then compare different ecosystems to highlight an important common pattern: the biomass matter pyramid. In most ecosystems there is more organic matter in producers than in herbivores and more organic matter in herbivores than in carnivores. They will use carbon-transforming processes to explain this pattern in Lesson 3.

Guiding Question

What are the patterns in biomass in ecosystems?

Activities in this Lesson

  • Activity 2.1: Predictions About Patters in Ecosystems (30 min)
  • Activity 2.2: The Meadow Simulation (50 min)
  • Activity 2.3: Evidence-Based Arguments About Patterns in Ecosystems (40 min)

Objectives

  1. Describe the “biomass pyramid” (producers > herbivores > carnivores) as a consistent pattern in terrestrial ecosystems.

NGSS Performance Expectations

Middle School

  • 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-LS2-4. 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-LS2-1. Analyze and interpret data to provide evidence for the effects of resource availability on organisms and populations of organisms in an ecosystem.

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.

Background Information

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.

Activity 2.1 introduces the key concept of biomass. 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 biomass of populations of producers, herbivores, and carnivores in an ecosystem and make predictions about biomass of each group in a meadow.

In Activity 2.2 students use an online simulation to investigate the relative sizes of the biomass of populations 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 biomass of the populations over a 100-year period.

Through the online simulations students will need to notice two patterns: 1) the amount of biomass in the populations of producers, herbivores, and carnivores changes over time based on resource availability and 2) over time a consistent pattern emerges: The amount of biomass in the rabbit population is smaller than the grass biomass, and biomass in the fox population is always the smallest. Different initial biomass of grasses, rabbits and foxes lead to different patterns of change, but the foxes can survive only if the grass biomass stays large.

In Activity 2.3 students complete the Evidence-Based Arguments Tool for the patterns in ecosystems that they observed in the Meadow Simulation. Then they observe the same pattern in producers, herbivores, and carnivores in four different types of ecosystems. (Ecologists would say that this pattern 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 biomass stored in consumers. This is not an important point for this Unit.)