MS-LS2-2: Ecosystem Interactions

MS-LS2-2
Ecosystem Interactions

Middle School

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Learning Objectives

• Identify predatory, competitive, and mutually beneficial interactions among different organisms.

• Explain how these interaction patterns are consistent across various ecosystems.

• Use a food web to explain energy flow and predict effects of population changes.

• Analyze how resource availability causes population changes within an ecosystem.

Key Vocabulary

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Ecosystem

An ecosystem includes all living organisms in an area, interacting with their non-living physical environment.

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Food Web

A food web is a model showing how energy flows through an ecosystem’s many interconnected food chains.

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Producer

A producer is an organism, like a plant, that creates its own food using energy from the sun.

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Consumer

A consumer is an organism that gets its energy by feeding on other organisms in a food chain.

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Decomposer

A decomposer breaks down dead organic material and returns important nutrients back into the soil and ecosystem.

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Predation

Predation is a biological interaction where a predator hunts and kills its prey for food.

Key Vocabulary

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Competition

Competition occurs when organisms struggle for the same limited resources to meet their basic needs.

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Mutualism

Mutualism is a close relationship between two different species where both of the organisms benefit.

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Abiotic Factors

Abiotic factors are the non-living chemical and physical parts of an ecosystem, like sunlight.

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Biotic Factors

Biotic factors include all of the living or once-living organisms in an entire ecosystem.

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Understanding Food Webs

• A food web models the flow of energy and matter in an ecosystem.

• ​Producers make food, consumers eat others, and decomposers recycle nutrients.

• Arrows in a food web show the direction that the energy flows.

• They show that consumers eat a variety of organisms and may compete.

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Multiple Choice

What is the primary purpose of a food web?

• To model the flow of energy and matter in an ecosystem.

• To list all the animals that live in a habitat.

• To show how decomposers recycle nutrients for plants.

• To describe the climate of a particular environment.

Multiple Choice

In a food web diagram, what does an arrow pointing from grass to a rabbit represent?

• It indicates that energy is transferred from the grass to the rabbit.

• It shows that the rabbit helps the grass grow.

• It means the rabbit and the grass are competing for resources.

• It signifies that the grass is a consumer of the rabbit.

Multiple Choice

If a disease significantly decreased the population of a primary consumer in a food web, what would be the most likely immediate effect on the ecosystem?

• The number of producers would suddenly increase.

• Competition between consumers for the remaining food sources would increase.

• Decomposers would have nothing left to break down.

• The total energy in the ecosystem would increase.

Types of Interactions

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Predatory Interactions

• A predator hunts and consumes another organism, which is called prey.

• This interaction can reduce the population size of the prey species.

• For instance, a lion hunting a zebra is a predatory interaction.

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Competitive Interactions

• This occurs when organisms need the same limited resources like food.

• Competition can happen between members of the same or different species.

• It affects the growth and survival of the organisms involved.

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Mutually Beneficial

• This is a relationship where two different species benefit from interacting.

• Both organisms gain something positive from their close association with each other.

• Sometimes one organism cannot survive without its partner in the relationship.

Multiple Choice

What general topic do predatory, competitive, and mutually beneficial relationships describe?

• The different ways organisms interact with each other.

• How organisms are classified into different groups.

• The way specific animals hunt for their prey.

• How the population of a single species can grow.

Multiple Choice

What is the key difference in the outcome for the organisms involved in a predatory interaction versus a mutually beneficial one?

• In a predatory interaction one organism is harmed, while in a mutually beneficial one, both organisms gain.

• Predatory interactions reduce population size, while mutually beneficial ones always increase it.

• Predatory interactions involve hunting, while mutually beneficial ones are about sharing limited resources.

• Both interactions occur between members of the same species to ensure their survival.

Multiple Choice

If two different species living in the same habitat both depend on the same limited source of food, what is the most likely outcome if that food source becomes scarce?

• The growth and survival of both populations will be negatively affected due to increased competition.

• One species will begin hunting the other species, turning it into a predatory interaction.

• The two species will form a mutually beneficial relationship to help each other survive.

• The populations will not be affected, as they will find other resources to use.

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Seasonal Changes in Mono Lake

Winter

• During winter, the lake's surface appears lifeless, but the water turns a vibrant green color.

• This color is caused by an explosive growth in the population of planktonic algae.

• Algae predators are dormant, and resources like light and nutrients are plentiful for growth.

Spring

• In spring, the warmer weather and increased sunlight cause brine shrimp and flies to hatch.

• These hungry predators begin to feast on the large population of green algae.

• They eat the algae so quickly that the population declines and the lake becomes clear again.

Multiple Choice

What causes Mono Lake to turn a vibrant green color during the winter?

• The water getting colder and freezing at the surface.

• An explosive growth in the population of planktonic algae.

• Brine shrimp and flies hatching in large numbers.

• The reflection of the sky on the water's surface.

Multiple Choice

What is the primary reason for the decrease in the algae population during the spring?

• The algae population running out of nutrients and light.

• The water becoming too warm for the algae to survive.

• The hatching of brine shrimp and flies that feed on the algae.

• The lake's water level rising and diluting the algae.

Multiple Choice

What would most likely happen in Mono Lake if an unusually cold spring prevented the brine shrimp and flies from hatching?

• The lake would immediately become clear.

• The lake would remain green for a longer period.

• The algae would run out of resources and die off.

• The brine shrimp and flies would find other food.

Mono Lake: Summer and Fall

• Migrating birds, like gulls, arrive and feast on brine shrimp and flies.

• The brine shrimp population rapidly declines due to lack of food and predation.

• In the fall, nutrient turnover allows the algae population to reproduce again.

Multiple Choice

What is the primary activity of migrating gulls when they arrive at Mono Lake in the summer?

• They build nests for the winter.

• They help the algae population to grow.

• They feed on the local brine shrimp and flies.

• They begin their migration south for the winter.

Multiple Choice

How is the brine shrimp population affected by the events of the summer?

• By migrating to a different part of the lake.

• By being eaten by birds and having a limited food supply.

• By the lake's water level decreasing in the summer.

• By the nutrient turnover that happens in the fall.

Multiple Choice

Based on the relationships described, what would be the most likely impact the following summer if the fall nutrient turnover did not occur?

• The birds would find a different food source in the lake.

• The brine shrimp population would not recover, leading to less food for the birds.

• The flies would become the main food source for all the birds.

• The nutrient levels in the lake would remain high throughout the next year.

Patterns Across Ecosystems

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Competitive Interactions

• Organisms compete for the same limited resources like food and space.

• This interaction can limit the size of a competing population.

• Rams fighting for mates is an example of this interaction.

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Predatory Interactions

• One organism, the predator, hunts and eats another, the prey.

• This affects the population sizes of both predators and their prey.

• A fox hunting a rabbit is a classic predatory interaction.

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Mutually Beneficial

• Two different species interact in a way that benefits them both.

• This relationship helps both species survive and reproduce more successfully.

• Bees get food from flowers while helping them to reproduce.

Multiple Choice

When organisms require the same limited resources, such as food and space, what type of interaction occurs?

• Competitive interaction

• Predatory interaction

• Mutually beneficial interaction

• Reproductive interaction

Multiple Choice

How are competitive and predatory interactions similar in their effect on an ecosystem?

• They both involve one organism hunting another.

• They can both limit the size of a population.

• They both result in both species benefiting.

• They only occur between animals of the same species.

Multiple Choice

In an ecosystem with foxes, rabbits, bees, and flowers, a sudden disease drastically reduces the rabbit population. Based on the relationships described, what is the most likely consequence?

• The fox population will likely decrease due to a lack of food.

• The bee population will increase because there are fewer rabbits.

• The fox population will switch to eating flowers to survive.

• The bee and fox populations will start to compete for resources.

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Common Misconceptions

Misconception	Correction
Arrows in a food web point from the predator to the prey.	Arrows show energy flow, from the organism that is eaten to the organism that eats it.
An ecosystem is a static, unchanging environment.	Ecosystems are dynamic; populations change with seasons, food, and predation.
Competition only happens between animals of the same species.	Competition can occur between different species that rely on the same limited resources.

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Summary

• Organism interactions like predation and competition are consistent across all ecosystems.

• A food web shows how energy flows through feeding relationships.

• Population sizes are controlled by predation and the availability of resources.

• Seasonal cycles of population change are driven by biotic and abiotic factors.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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