Community Interactions: Competition and Predation

Active learning works for this topic because competition and predation are dynamic processes that students can experience through simulation, data analysis, and real-world examples. Watching population cycles unfold or seeing adaptations emerge in real time makes abstract ecological principles concrete and memorable.

• 11th Grade
• Biology
• 4 activities
• 20 min–45 min

Learning Objectives

1. Compare and contrast the mechanisms and impacts of interspecific and intraspecific competition on population size and distribution.
2. Analyze the cyclical dynamics of predator and prey populations, explaining the role of coevolutionary adaptations.
3. Explain the competitive exclusion principle using Gause's Paramecium experiments and predict its effect on species coexistence.
4. Evaluate the role of keystone predators in maintaining community biodiversity by preventing competitive exclusion.
5. Synthesize data from population simulation models to illustrate the ripple effects of community interactions on trophic levels.

Simulation Game

⏱ 45 min·Pairs

Simulation Game: Predator-Prey Population Dynamics

Pairs of students simulate lynx-hare cycles using index cards over 12 rounds, recording population sizes after each round and plotting them on shared graph paper. The class compiles data to produce the characteristic oscillating curves, then discusses what drives the time lag between predator and prey peaks.

Prepare & details

Differentiate between interspecific and intraspecific competition and their effects on populations.

Facilitation Tip: Before starting the Predator-Prey Population Dynamics simulation, circulate and ask each group to predict what they think will happen to prey numbers in the first five rounds.

Setup: Flexible space for group stations

Materials: Role cards with goals/resources, Game currency or tokens, Round tracker

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Inquiry Circle

⏱ 40 min·Small Groups

Inquiry Circle: Competitive Exclusion vs. Coexistence

Groups analyze a published dataset of barnacle settlement patterns or Paramecium growth curves to determine whether competitive exclusion or niche-based coexistence occurred. They must identify which resource was limiting and whether niche differentiation was sufficient to allow coexistence.

Prepare & details

Analyze the coevolutionary arms race between predators and prey.

Facilitation Tip: During the Competitive Exclusion vs. Coexistence investigation, have students document their warbler feeding zone observations in a shared digital document so all groups can see the emerging pattern.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Think-Pair-Share

⏱ 20 min·Pairs

Think-Pair-Share: Sea Otter Trophic Cascade

Students read a one-page summary of the sea otter-urchin-kelp system in the Pacific Northwest. Pairs must explain the chain of effects that follows sea otter removal and articulate why this qualifies as a trophic cascade rather than a simple two-species interaction.

Prepare & details

Explain how the competitive exclusion principle influences species distribution.

Facilitation Tip: For the Sea Otter Trophic Cascade Think-Pair-Share, provide printed food web diagrams so students can annotate changes as they discuss rather than trying to hold all details in their heads.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Gallery Walk

⏱ 35 min·Small Groups

Gallery Walk: Arms Race Adaptations

Stations display paired photographs of predator-prey arms races: the bombardier beetle and its predators, crypsis in walkingsticks, the death's-head hawkmoth infiltrating bee colonies. Students explain the reciprocal adaptations at each station and predict the likely next evolutionary step in the arms race.

Prepare & details

Differentiate between interspecific and intraspecific competition and their effects on populations.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Teaching This Topic

Teach this topic by starting with the most vivid examples first: predator-prey cycles from lynx-hare data before moving to competition concepts. Avoid overloading students with too many terms at once; instead, have them discover principles through structured exploration. Research shows that students grasp oscillating relationships better when they manipulate variables themselves rather than receive lectures about them.

What to Expect

Successful learning looks like students confidently distinguishing interspecific and intraspecific competition, explaining how predator-prey cycles maintain balance, and justifying why competitive exclusion is rare in nature. They should apply these concepts to new scenarios and recognize their role in shaping biodiversity.

Watch Out for These Misconceptions

Common Misconception

During the Predator-Prey Population Dynamics simulation, students may expect prey populations to drop steadily to zero and remain there.

What to Teach Instead

During the Predator-Prey Population Dynamics simulation, remind students to record population numbers every two rounds and look for the cyclical pattern that emerges. Ask them to explain why the prey numbers never hit zero in their data tables, pointing to the carrying capacity of the environment.

Common Misconception

During the Collaborative Investigation: Competitive Exclusion vs. Coexistence, students might assume that any two species competing for the same resource will always lead to the exclusion of one species.

What to Teach Instead

During the Collaborative Investigation: Competitive Exclusion vs. Coexistence, have students measure the actual feeding zones of the warbler species and calculate the percentage overlap. Ask them to explain how even 10% niche differentiation allows coexistence, using their recorded measurements as evidence.

Common Misconception

During the Think-Pair-Share: Sea Otter Trophic Cascade activity, students may believe intraspecific competition is always less important than interspecific competition.

What to Teach Instead

During the Think-Pair-Share: Sea Otter Trophic Cascade activity, direct students to the sea otter population density data and ask them to calculate per-capita growth rates at low versus high density. Have them explain why reduced per-capita growth at high density indicates strong intraspecific competition.

Assessment Ideas

Quick Check

After students finish the Competitive Exclusion vs. Coexistence investigation, present two new scenarios: a community garden with two tomato plant varieties and a forest with wolves hunting deer. Ask students to identify each interaction type and justify their answers in one sentence using evidence from their investigation.

Discussion Prompt

After the Gallery Walk: Arms Race Adaptations, pose the question: 'How might the introduction of an invasive predator species disrupt the established community interactions in this ecosystem?' Facilitate a discussion where students apply predator-prey dynamics and coevolution concepts to predict outcomes, referencing specific adaptations observed during the gallery walk.

Exit Ticket

During the Predator-Prey Population Dynamics simulation, have students draw a simple graph showing the oscillating population sizes of their predator and prey over time. Below the graph, ask them to write two sentences explaining the relationship between the two population curves and one example of a coevolutionary adaptation their species might develop based on their simulation experience.

Extensions & Scaffolding

• Challenge early finishers to design their own predator-prey simulation with a carrying capacity limit and explain how it changes the population curves.
• Scaffolding for struggling students: Provide a partially completed data table for the Predator-Prey simulation with the first three rounds filled in to help them identify the pattern.
• Deeper exploration: Have students research an actual invasive species case study and present its impact on local predator-prey relationships using the community interaction concepts they've learned.

Key Vocabulary

Interspecific Competition	Competition for limited resources that occurs between individuals of different species, potentially leading to reduced population growth or exclusion.
Intraspecific Competition	Competition for limited resources that occurs between individuals of the same species, often more intense due to identical resource needs.
Competitive Exclusion Principle	The principle stating that two species competing for the exact same limited resources cannot stably coexist; one species will eventually outcompete and eliminate the other.
Predator-Prey Dynamics	The interaction where one organism (predator) hunts and kills another organism (prey) for food, influencing the population sizes of both.
Coevolution	The process where two or more species reciprocally influence each other's evolution, often seen in predator-prey relationships as adaptations develop in response to each other.
Keystone Species	A species that has a disproportionately large effect on its environment relative to its abundance, often by controlling populations of other species and maintaining community structure.