Web of changes

This exercise is a part of Educator Guide: The Case of the Arctic’s Missing Ice / View Guide

Purpose: Students will think through and diagram an Arctic and local food web and will explore how ecosystem disruptions can impact the food webs.

Procedural overview: After reading the Science News article “The case of the Arctic’s missing ice,” students will describe the Arctic food web and the factors that are impacting it, including proposing a mathematical model and experiment to explore how one population changes over time. Students will then apply similar methods to a food web in their local ecosystem.

Approximate class time: 1 to 2 class periods (depending on the depth of investigation into a local ecosystem).


Activity Guide for Students: Web of Changes

Online access or resource books to look up information on organisms and food webs

Directions for teachers:

Review the basics of ecosystems, trophic levels, food chains, food webs and the factors that influence population size with the class as necessary. Have your students read the article “The case of the Arctic’s missing ice,” in the March 16 issue of Science News, and ask them to work through the activity below. The activity asks students to create a simple food web, define factors that affect its stability and predict and graph how a change in one factor will disrupt the web’s stability.

After students complete the questions for the Arctic food web, have them apply the learned concepts to a local ecosystem by designing a more comprehensive food web and thinking about the factors that are disrupting it, or might in the future. If time permits, consider having students answer Questions 4 and 5 for their local ecosystem.

Depending on time, you can also encourage students to get creative with the presentation of their food webs. They can draw or print images of the organisms to make their diagrams more engaging.

Directions for students:

Food chains and food webs help us visualize how energy and matter move among trophic levels in an ecosystem. Use the Arctic ecosystem described in the article “The case of the Arctic’s missing ice” to answer the following questions.

1. Create a simple food web for the Arctic ecosystem described using examples from the article. Include at least 10 organisms, and use arrows to show the direction of energy flow between organisms. Identify the roles of different organisms (as outlined below). Some organisms may have more than one role.

Primary consumer
Secondary consumer
Tertiary consumer

Students answers will vary but should include organisms mentioned in the article. A sample diagram offers an example of what a student diagram might look like — it is not comprehensive.

2. What factors affect the stability and carrying capacity of this Arctic ecosystem?

Boundaries with land, amounts and locations of sea ice, sunlight, temperatures throughout the year, ocean currents, nutrient input, and amounts of fishing and hunting by humans.

3. Choose one factor listed above and predict how a change in that factor over time could lead to a disruption in the stability of organisms mentioned in your food web.

Less sea ice formation can lead to fewer or smaller cold pools of salty water near the ocean floor. Without those cold, salty pools, Arctic cod will have fewer refuges to grow, which could lead to a decline in Arctic cod. A decline in Arctic cod could lead to a decline in polar bears, seals, whales, thick billed murres and other seabirds.

4. Pick one organism and graph the predicted population change over time due to the disruption you’ve chosen. Determine a possible mathematical model for this change.

Responses will vary, but students should consider the food sources available to the organism, predator population sizes and the abundance of the organisms’ preferred habitat. A stable population will remain constant over time. A population with abundant resources and few predators may grow exponentially until it reaches its carrying capacity, at which time it may remain constant or crash. A population with diminishing resources and a greater number of predators will face exponential decay, or could crash linearly in the absence of vital resources.

5. Propose a simple observational study to test your model. (Assume you have enough resources, funding and time. You do not actually have to do any experiments.)

Students’ experiments will likely rely on observation methods to monitor the population of a particular organism over time. Observational techniques might include direct human observation, monitoring of animal tracks, analyses of animal wastes, thermal and other imaging, image recognition software, DNA sampling, chemical analysis and so on. Students may consider where to put the sensors (on land, on or under the sea, in the air, on satellites), how many sensors to deploy, what area to cover and how to estimate the population that is not directly detected by the sensors. Students may consider how many years to continue the monitoring program before reaching conclusions about population changes.

Directions for students continued:

Now relate the information, examples and answers given about the Arctic ecosystem to a local ecosystem using the prompts and questions that follow.

6. Research and choose a local ecosystem. Create a more comprehensive food web for your local ecosystem. It should include:

At least 25 organisms (be sure to include some examples of plants, fungi and bacteria)
Arrows to show the direction of energy flow between organisms
All the trophic levels at which organisms feed:

Primary consumer
Secondary consumer
Tertiary consumer

Student responses will vary, but should be comparable to the model presented for the Arctic food web.

7. What factors affect the stability and carrying capacity of this ecosystem?

Student responses will vary, but responses may include geographic or human-made features that define the boundaries of that ecosystem, the resources available within that ecosystem (soil, water, sun and so on), climate and weather (including cycles throughout the day and throughout the year), and competition from neighboring ecosystems and/or from humans.

8. What factors are currently disrupting your chosen ecosystem, or may disrupt it in the future?

Student responses will vary, but responses may include climate change, encroachment by humans (more roads, more houses, noise, artificial lighting), pollution, infectious diseases, introduction of domestic animals such as cats and dogs, invasive species, farming and farm runoff, fishing and hunting, as well as natural disasters.

9. Choose one of these potential disruptors and predict the cascade of effects over time for one organism in the food chain.

Student responses will vary.

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