Science · Grade 9 · Sustainable Ecosystems and Stewardship · Term 1

Community Interactions: Competition & Predation

Exploring how competition and predation shape species populations and ecosystem structure.

• Ontario Curriculum Expectations
• HS-LS2-2

About This Topic

Community interactions like competition and predation regulate species populations and maintain ecosystem balance. Students examine interspecific competition, where species vie for limited resources such as food or habitat, often resulting in resource partitioning or competitive exclusion. Predation involves predators controlling prey numbers through direct consumption, creating dynamic population cycles observable in Canadian ecosystems like wolf-moose interactions in Algonquin Park.

This topic aligns with Ontario's Sustainable Ecosystems and Stewardship unit by fostering analysis of human impacts, such as invasive species introductions that disrupt native communities. Students predict outcomes like population crashes from new predators or niche specialization through partitioning, building skills in modeling interactions and data interpretation.

Active learning shines here because abstract dynamics become concrete through simulations. When students participate in predator-prey games or competition role-plays, they witness cycles and partitioning firsthand, leading to deeper retention and ability to apply concepts to real-world stewardship issues.

Key Questions

1. Analyze how interspecific competition can lead to resource partitioning.
2. Predict the long-term effects of introducing a new predator into an ecosystem.
3. Differentiate between competitive exclusion and resource partitioning.

Learning Objectives

• Analyze how interspecific competition influences the distribution and abundance of species within a given habitat.
• Predict the population dynamics of a prey species following the introduction of a novel predator.
• Compare and contrast the outcomes of competitive exclusion and resource partitioning in stable ecosystems.
• Evaluate the impact of invasive species on native community interactions, specifically competition and predation.
• Explain the mechanisms by which predation regulates prey populations in Canadian ecosystems.

Before You Start

Food Webs and Trophic Levels

Why: Students need to understand how energy flows through an ecosystem to grasp the roles of predators and prey and the concept of competition for resources.

Introduction to Ecosystems

Why: A foundational understanding of what an ecosystem is, including biotic and abiotic factors, is necessary before exploring interactions within them.

Key Vocabulary

Interspecific Competition	A type of interaction where individuals of different species compete for the same limited resources, such as food, water, or territory.
Resource Partitioning	The division of limited resources by species that coexist, allowing them to use the same resources in a different way or at a different time to reduce competition.
Competitive Exclusion	The principle that two species competing for the exact same limiting 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.
Niche	The role and position a species has in its environment, including how it meets its needs for food and shelter, how it survives, and how it reproduces.

Watch Out for These Misconceptions

Common Misconception

The strongest species always eliminates competitors.

What to Teach Instead

Competitive exclusion occurs only without partitioning; species often divide resources by behavior or timing. Role-plays let students test strategies, revealing coexistence possibilities and challenging dominance myths through trial and data.

Common Misconception

Predators constantly wipe out prey populations.

What to Teach Instead

Populations cycle due to predator dependence on prey; low prey limits predators. Simulations with rounds show rebounds, helping students graph oscillations and grasp density dependence via active modeling.

Common Misconception

Competition happens only between similar species.

What to Teach Instead

Interspecific competition affects diverse species sharing niches. Station activities expose varied pairings, with peer predictions and observations correcting narrow views through collaborative evidence-building.

Active Learning Ideas

Simulation Game: Predator-Prey Bean Hunt

Scatter green beans (prey) and red lentils (predators) on the floor. Pairs act as predators collecting prey in 1-minute rounds, recording captures. Over 10 rounds, graph population trends to observe cycles. Discuss factors like predator efficiency.

45 min·Pairs

Role-Play: Resource Partitioning

Assign small groups species roles competing for paper resources (food, space). Introduce scarcity, then guide partitioning strategies like time or location shifts. Groups present adaptations and vote on survival likelihood.

35 min·Small Groups

Stations Rotation: Competition Scenarios

Set up stations with models: exclusion (one species dominates), partitioning (shared niches), predation webs. Groups rotate, predict outcomes, and adjust variables like resource levels. Compile class data for patterns.

50 min·Small Groups

Invasive Predator Introduction

Use whole class as ecosystem; introduce 'invasive' volunteers as new predators. Track prey decline over rounds with counters. Debrief long-term effects and stewardship solutions.

30 min·Whole Class

Real-World Connections

• Wildlife biologists in Jasper National Park monitor elk and wolf populations to understand how predator-prey dynamics affect vegetation health and overall ecosystem stability.
• Conservationists working to protect endangered species, such as the Vancouver Island marmot, study interspecific competition with introduced species to develop effective management strategies.
• Fisheries managers assess predator-prey relationships in the Great Lakes to predict the impact of invasive fish species, like the zebra mussel, on native fish populations and food webs.

Assessment Ideas

Quick Check

Present students with a scenario describing two species in a habitat with a shared food source. Ask them to identify the type of interaction (competition) and predict whether competitive exclusion or resource partitioning is more likely to occur, justifying their answer.

Discussion Prompt

Facilitate a class discussion using the prompt: 'Imagine a new bird species is introduced to an area with established insectivorous birds. What are two ways this new species could impact the native bird populations, and what evidence would you look for to support your predictions?'

Exit Ticket

Provide students with a diagram of a simple food web. Ask them to circle one predator-prey relationship and one competitive relationship. Then, have them write one sentence explaining how removing the predator would affect the prey population.

Frequently Asked Questions

How does resource partitioning prevent competitive exclusion?

Resource partitioning allows species to coexist by specializing in niche aspects like food size or foraging time, reducing overlap. Students model this by dividing class resources unequally yet sustainably, observing stable populations. This connects to Ontario ecosystems where warblers partition insects by height, promoting biodiversity understanding.

What are long-term effects of introducing a new predator?

New predators can cause prey declines, secondary trophic cascades, and ecosystem shifts, as seen with wolves in some areas. Predictions involve food web diagrams; students simulate introductions to track multi-year impacts, emphasizing stewardship like monitoring invasives in the Great Lakes.

How can active learning help teach competition and predation?

Active simulations like bean hunts or role-plays make invisible dynamics visible, as students embody roles and track real-time changes. This builds intuition for cycles and partitioning over lectures. Collaborative graphing reinforces data skills, with debriefs linking to Canadian case studies for lasting comprehension.

How to differentiate intraspecific from interspecific competition?

Intraspecific is within species for mates or territory; interspecific crosses species for shared resources. Use paired comparisons: students chart examples from local ponds, like ducks vs. fish for plankton. Group debates clarify distinctions, aiding precise analysis in ecosystem models.