Students who demonstrate understanding can: Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
Clarification statement: Emphasis is on recognizing patterns in data and making warranted inferences about changes in populations, and on evaluating empirical evidence supporting arguments about changes to ecosystems.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
Ecosystems are always changing. A wildfire, a flood, a dam, a new invasive species or the loss of a predator can shift which populations thrive and which decline. Students construct arguments supported by empirical evidence: they look at population data from before and after a disruption and argue whether the change caused the shift. Physical components include water, temperature, soil and sunlight; biological components include the organisms themselves.
A famous case is the return of wolves to a national park. Elk numbers fell, young willow and aspen trees recovered along streams, and beaver populations increased. Another is an invasive mussel that filters huge amounts of plankton from a lake, leaving less food for native fish. In each case students should identify the change, trace its effects through the food web, and judge whether the evidence actually supports the claimed cause.
Evaluating evidence is part of the work, so students also ask whether other factors could explain the data and whether the sample is large enough.
Because organisms are linked in food webs, a change to one population, such as removing a predator, often spreads to many other species.
Some ecosystems recover after a disturbance, but large or permanent changes can shift them to a different state with different populations.
Two populations changing at the same time does not prove one caused the other. Students should look for a mechanism and rule out other explanations.
Before an invasive filter-feeding mussel arrived, a lake had about 400 plankton per liter and a native fish count of 1,200. Five years later, plankton fell to 80 per liter and the fish count to 500. Argue whether the mussel affected the fish.
Answer: The data support the claim: plankton dropped from 400 to 80 per liter and fish from 1,200 to 500 after the mussels arrived, consistent with less food for fish, although a comparison lake would make the argument stronger.
Case studies with real-style data work best, such as wolves and elk, invasive species, or a drought year. Have students write an argument, then trade with a partner who must identify a possible alternative explanation.
Assessment tasks emphasize recognizing patterns in data and judging the strength of evidence, so make 'what else could explain this?' a routine question.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: D) Rainfall
Rainfall is nonliving. Deer, fungi and grass are biological components.
Answer: A) Fewer elk were eating young trees
With fewer elk browsing, young trees had a better chance to grow.
Answer: invasive species (also accepted: invasive, an invasive species, non-native species)
Invasive species can outcompete or prey on native species.
Answer: C) Sun-loving plants and grasses
With the tree canopy gone, more light reaches the ground, so sun-loving plants spread.
Answer: D) Look for a mechanism and rule out other causes
Correlation is not proof; scientists check for a link and other explanations.
Answer: physical (also accepted: a physical change)
Water flow is a nonliving, physical component.
Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.*
A full lesson with slides, activities and an exit ticket on ecosystem changes affect populations, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on MS-LS2-4 with an answer key, ready in about a minute.
Make a worksheet βTurn ecosystem changes affect populations into a quiz students answer online that marks itself, with a class summary for you.
Build a test βEmpirical data, such as population counts before and after a change, which students use to argue that ecosystem changes affect populations.
Changes to physical components, such as water or temperature, and to biological components, such as the arrival or loss of a species.