Science · Grade 7 · Interactions within Ecosystems · Term 1

Biotic Limiting Factors: Competition & Predation

Exploring the biological constraints that determine the carrying capacity of a habitat, such as competition and predation.

• Ontario Curriculum Expectations
• MS-LS2-1

About This Topic

Biotic limiting factors such as competition and predation shape the carrying capacity of habitats by regulating population sizes. Students differentiate intraspecific competition, where members of the same species vie for limited resources like food or territory, from interspecific competition between different species. They also analyze predator-prey relationships, where predators help control prey numbers to prevent overpopulation and resource depletion.

This topic aligns with Ontario Grade 7 science expectations on interactions within ecosystems. Students investigate how these factors maintain balance, predict outcomes like population cycles from real data on lynx and hare, and consider disruptions from introducing new predators. Such analysis fosters understanding of dynamic equilibrium in ecosystems.

Active learning shines here through simulations and models that reveal population fluctuations over time. When students role-play competitions or track bean 'prey' hunted by 'predators,' they witness cause-and-effect relationships firsthand, making abstract concepts concrete and building skills in prediction and data interpretation.

Key Questions

1. Differentiate between interspecific and intraspecific competition.
2. Analyze how predator-prey relationships regulate population sizes.
3. Predict the long-term effects of introducing a new predator into an ecosystem.

Learning Objectives

• Compare and contrast intraspecific and interspecific competition using specific examples of resource limitation.
• Analyze data from predator-prey population graphs to explain how each population regulates the other.
• Predict the potential impact on an ecosystem's carrying capacity if a new predator is introduced.
• Explain the role of competition and predation in maintaining the carrying capacity of a given habitat.

Before You Start

Food Chains and Food Webs

Why: Students need to understand the flow of energy through ecosystems and identify producers, consumers, and decomposers to grasp predator-prey interactions.

Basic Needs of Living Things

Why: Understanding that organisms require resources like food and shelter is fundamental to comprehending competition for those resources.

Key Vocabulary

Intraspecific Competition	Competition for resources that occurs between individuals of the same species. This can include competition for food, water, mates, or territory.
Interspecific Competition	Competition for resources that occurs between individuals of different species. This can happen when species share a limited resource, like food or living space.
Predation	An interaction where one organism, the predator, hunts and kills another organism, the prey, for food. This relationship influences the population sizes of both species.
Carrying Capacity	The maximum population size of a biological species that can be sustained in that specific environment, given the available resources and environmental conditions.

Watch Out for These Misconceptions

Common Misconception

Competition only happens between different species.

What to Teach Instead

Intraspecific competition occurs within species for scarce resources and often limits population growth more intensely. Role-playing scenarios with identical 'animals' helps students see this dynamic, as they experience crowding firsthand during active competitions.

Common Misconception

Predator populations always stay larger than prey.

What to Teach Instead

Prey outnumber predators in balanced systems, with cycles where prey booms lead to predator increases then crashes. Simulations using beans or cards let students track these oscillations, correcting the idea through visible data patterns and group discussions.

Common Misconception

Introducing a new predator always stabilizes the ecosystem.

What to Teach Instead

New predators can cause prey crashes or invade niches, leading to imbalances. Prediction activities with models allow students to test scenarios, observe unintended effects, and refine their understanding via peer feedback.

Active Learning Ideas

Simulation Game: Predator-Prey Chase

Scatter 100 beans (prey) on the floor; pairs act as predators collecting beans in 1-minute rounds while 'prey' decreases each round. Graph population changes over 10 rounds. Discuss how predation limits prey growth.

45 min·Pairs

Stations Rotation: Competition Scenarios

Set up stations with limited resources: food bowls for intraspecific (same animal cutouts), territory maps for interspecific (different species). Small groups compete, record winners, and rotate. Compare outcomes in class share-out.

50 min·Small Groups

Data Analysis: Lynx-Hare Graphs

Provide historical population graphs; individuals plot trends, identify cycles, and predict effects of removing predators. Pairs present predictions with evidence from data.

35 min·Individual

Role-Play: New Predator Introduction

Whole class divides into prey, original predators, and new predators. Simulate hunts over rounds, adjusting numbers based on 'success.' Debrief on ecosystem changes.

40 min·Whole Class

Real-World Connections

• Wildlife biologists studying deer populations in Algonquin Park track competition for food and space, especially during winter, to understand population health and inform management strategies.
• Fisheries managers monitor predator-prey dynamics, such as the relationship between lake trout and smaller fish species in the Great Lakes, to set sustainable fishing quotas and prevent ecosystem imbalances.
• Conservationists assess the impact of introducing non-native predators, like the brown tree snake to Guam, which has devastated native bird populations due to a lack of natural defenses.

Assessment Ideas

Quick Check

Present students with two scenarios: 1) Squirrels competing for acorns in a forest, and 2) A fox hunting rabbits. Ask students to identify which scenario represents intraspecific competition and which represents interspecific competition, and to justify their answers.

Discussion Prompt

Pose the question: 'Imagine a new, highly effective predator is introduced to an area with rabbits and foxes. What are two possible outcomes for the rabbit population and two possible outcomes for the fox population? Explain your reasoning.' Facilitate a class discussion on their predictions.

Exit Ticket

Ask students to draw a simple diagram illustrating a predator-prey relationship. They should label the predator and prey and write one sentence explaining how this interaction affects the population size of the prey.

Frequently Asked Questions

How do biotic factors like competition limit carrying capacity?

Competition for resources such as food, water, or space restricts how many organisms a habitat supports, while predation keeps prey populations in check. Students analyze examples like wolves competing intraspecifically for territory or foxes preying on rabbits, using graphs to see how these factors prevent overpopulation and maintain ecosystem health.

What is the difference between intraspecific and interspecific competition?

Intraspecific involves same-species members competing, often leading to emigration or death, like deer fighting over grass. Interspecific pits different species against each other, such as squirrels and birds for nuts. Activities with resource stations clarify this by letting students compete in both setups and compare intensities.

How can active learning help teach predator-prey relationships?

Simulations where students act as predators 'hunting' beans as prey make cycles visible, as populations fluctuate round by round. Graphing class data reinforces patterns, while discussions connect observations to real ecosystems like lynx-hare. This hands-on approach builds intuition for regulation better than lectures alone, with 75-80% retention gains from such kinesthetic methods.

What happens when a new predator enters an ecosystem?

It can reduce prey numbers sharply, potentially causing predator starvation or affecting other species through cascades. Students predict via models, like adding 'invasive' hunters to simulations, learning long-term effects such as extinctions or new balances from Ontario examples like introduced fish in lakes.