Interspecific Interactions: Competition and Predation

Active learning works for this topic because interspecific interactions involve dynamic processes like population cycles and niche specialization, which students grasp more deeply through hands-on exploration. Simulations and case studies let students see cause-and-effect relationships in real time, making abstract evolutionary pressures tangible and memorable.

• 12th Grade
• Biology
• 4 activities
• 25 min–45 min

Learning Objectives

1. Analyze the impact of niche partitioning on the coexistence of competing species within a defined community.
2. Evaluate the evolutionary adaptations that have arisen in predator and prey populations due to reciprocal selective pressures.
3. Predict the potential consequences for community structure and stability following the introduction of an invasive competitor or predator.
4. Compare and contrast the outcomes of competitive exclusion and resource partitioning using case studies.
5. Synthesize information from ecological data to explain how interspecific interactions shape biodiversity.

Simulation Game

⏱ 45 min·Small Groups

Simulation Game: Predator-Prey Population Cycles

Student groups simulate predator and prey populations using cards or beans representing individual organisms. Each round, students calculate survival and reproduction, then adjust population counts. Groups graph population sizes over 10 rounds and identify the phase relationship between predator and prey peaks, comparing their results to Lotka-Volterra model predictions.

Prepare & details

Explain how niche partitioning and competition shape community structure.

Facilitation Tip: During the Gallery Walk, provide a graphic organizer with columns for species, resource, and adaptation to guide students' note-taking on niche partitioning examples.

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

Case Study Analysis

⏱ 35 min·Pairs

Case Study Analysis: Yellowstone Trophic Cascade

Pairs read a data summary of wolf reintroduction effects in Yellowstone and construct a cause-and-effect diagram tracing how wolf predation on elk affected riparian vegetation, beaver populations, and stream hydrology. Pairs present their diagrams and compare which indirect effects each pair identified, noting any that were overlooked.

Prepare & details

Analyze the evolutionary adaptations that arise from predator-prey relationships.

Setup: Groups at tables with case materials

Materials: Case study packet (3-5 pages), Analysis framework worksheet, Presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

Think-Pair-Share

⏱ 25 min·Pairs

Think-Pair-Share: Competitive Exclusion vs. Coexistence

Present data from two species of barnacles occupying different zones on a tidal rock face. Pairs explain which competitive mechanisms are operating, predict what would happen if one species were removed, and design a simple field experiment to test competitive exclusion in this system.

Prepare & details

Predict the outcome of introducing a new predator or competitor into an ecosystem.

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

⏱ 40 min·Small Groups

Gallery Walk: Niche Partitioning Examples

Post six stations showing data on niche partitioning in different communities, including MacArthur's warblers, lizard communities, and African savanna grazers. Student groups rotate, identify the resource axis along which each community is partitioned, and classify each as character displacement or ecological niche differentiation.

Prepare & details

Explain how niche partitioning and competition shape community structure.

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

Teachers should avoid oversimplifying the outcome of interspecific interactions, as real ecosystems often show coexistence rather than competitive exclusion. Use real-world examples to show students that outcomes depend on scale, resource abundance, and environmental context. Research suggests students develop stronger conceptual models when they first observe patterns in simulations before analyzing case studies.

What to Expect

By the end of these activities, students should be able to explain how competition and predation shape community structure, use evidence to support claims about niche partitioning, and predict outcomes of species introductions or removals. Look for accurate use of vocabulary and evidence-based reasoning in discussions and written responses.

Watch Out for These Misconceptions

Common Misconception

During the Think-Pair-Share: Competitive Exclusion vs. Coexistence, watch for students who assume the strongest competitor will always eliminate others, leading to monocultures in ecosystems.

What to Teach Instead

Use the Think-Pair-Share to redirect this misconception by having students examine real examples of niche partitioning in the gallery walk images, then revisit their initial assumptions about competition outcomes.

Common Misconception

During the Yellowstone Trophic Cascade Case Study, watch for students who claim predators harm ecosystems by reducing prey populations.

What to Teach Instead

Use the Yellowstone Case Study to correct this idea by having students analyze the primary literature showing how wolf reintroduction increased biodiversity and vegetation recovery, linking predator regulation to ecosystem health.

Common Misconception

During the Predator-Prey Population Cycles Simulation, watch for students who describe prey species as passive victims, overlooking their role in the evolutionary arms race.

What to Teach Instead

After the simulation, ask students to brainstorm prey adaptations that could alter the cycle, using the simulation results as evidence for reciprocal evolutionary pressures between predators and prey.

Assessment Ideas

Discussion Prompt

After the Think-Pair-Share: Competitive Exclusion vs. Coexistence, present students with a scenario: 'A new, highly efficient herbivore is introduced into a grassland ecosystem with several native herbivore species.' Ask: 'What are two ways this introduction could impact the existing herbivore community? How might niche partitioning or competitive exclusion play a role?'

Quick Check

During the Gallery Walk: Niche Partitioning Examples, provide students with a diagram showing two predator species and their shared prey. Ask them to label the types of interactions occurring and write one sentence explaining a potential evolutionary adaptation one of the predators might develop to reduce competition.

Exit Ticket

After the Predator-Prey Population Cycles Simulation, have students define 'niche partitioning' in their own words and provide one specific example of how it helps species coexist. They should also list one real-world profession that uses this ecological concept.

Extensions & Scaffolding

• Challenge early finishers to design their own predator-prey simulation with three species, including a keystone predator, and predict how removal of one species will affect the others.
• Scaffolding for struggling students: Provide a partially completed niche partitioning diagram with two species and ask them to add a third species that reduces competition.
• Deeper exploration: Have students research an introduced species in their region and prepare a short presentation on its ecological impacts, using niche partitioning or competitive exclusion to explain observed outcomes.

Key Vocabulary

Interspecific Competition	A type of interaction where individuals of different species compete for limited resources, such as food, water, or territory.
Niche Partitioning	The process by which competing species evolve to use different resources or use shared resources in different ways, reducing direct competition and allowing them to coexist.
Competitive Exclusion Principle	The concept that two species competing for the exact same limited resources cannot coexist indefinitely; one species will eventually outcompete and eliminate the other.
Predation	An interaction where one organism, the predator, hunts and kills another organism, the prey, for food.
Trophic Cascade	An ecological process that starts at the top of the food chain and tumbles down to lower levels, often initiated by the addition or removal of a top predator.