Interactions within Ecosystems

Interactions within Ecosystems

Middle School

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Learning Objectives

• Define biotic and abiotic factors and tell the difference between them.

• Explain energy flow using food chains, food webs, and trophic levels.

• Describe the key differences between competition, predation, and types of symbiosis.

• Analyze how interactions can affect populations within an ecosystem.

Key Vocabulary

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Ecology

The study of how living organisms interact with each other and their surrounding environment.

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Ecosystem

A community of all the biotic (living) and abiotic (non-living) things in a specific area.

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Niche

The specific role a species has in its ecosystem, including how it gets its food source.

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Food Chain

A diagram that shows a single path for the flow of energy within an ecosystem.

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Food Web

A diagram representing the many interconnected paths for energy flow in an entire ecosystem.

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Trophic Level

The feeding position an organism occupies within a food chain or a larger food web.

Key Vocabulary

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Competition

The struggle between organisms to get the same limited resources, like food, water, or space.

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Predation

A relationship where one animal, the predator, hunts and eats another animal, known as the prey.

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Symbiosis

A close, long-term interaction between two different species that are living in close physical association.

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Mutualism

A symbiotic relationship between two different species in which both of the organisms receive a benefit.

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Commensalism

A symbiotic relationship where one species benefits while the other species is not affected at all.

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Parasitism

A symbiotic relationship where one species benefits by living on or inside the other, harming it.

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The Structure of an Ecosystem

• An ecosystem includes living (biotic) and non-living (abiotic) parts.

• Every species has a niche, which is its unique role.

• A niche includes its habitat, what it eats, and its interactions.

• Two species cannot occupy the exact same niche in one habitat.

Multiple Choice

What are the two main components that make up an ecosystem?

• Living (biotic) and non-living (abiotic) parts

• Sunlight and water only

• A species' habitat and its food

• Plants and animals only

Multiple Choice

Which of the following best describes a species' niche?

• The specific location where an animal sleeps

• The total number of animals in the ecosystem

• Its unique role, including its habitat and what it eats

• The non-living parts of its environment

Multiple Choice

If a new species of bird that eats the same insects and lives in the same type of tree as a native bird is introduced to a habitat, what will most likely happen?

• The two species will compete with each other for the same niche

• The native bird will welcome the new species to the habitat

• The two species will learn to share the resources equally

• The new species will immediately find a different type of food

Energy Roles in an Ecosystem

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Producers (Autotrophs)

• Producers are organisms that are capable of making their own food.

• Photoautotrophs like plants use sunlight to create their own food source.

• Chemoautotrophs use chemical energy to make food instead of using sunlight.

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Consumers (Heterotrophs)

• Consumers get their energy by eating other living organisms for food.

• Herbivores eat producers, while carnivores mainly eat other consumers for energy.

• Omnivores are consumers that will eat both producers and other consumers.

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Decomposers

• Decomposers break down dead organisms and other organic waste products.

• They return essential nutrients back into the soil and the environment.

• This group includes scavengers, detritivores, and saprotrophs like fungi and bacteria.

Multiple Choice

Which statement best describes how producers, also known as autotrophs, get their energy?

• They get energy by eating other living organisms.

• They get energy by breaking down dead organisms.

• They make their own food using energy from sunlight or chemicals.

• They absorb energy directly from the soil and air.

Multiple Choice

What is the primary difference between the way herbivores and carnivores obtain energy?

• Herbivores make their own food, while carnivores eat dead organisms.

• Herbivores eat producers for energy, while carnivores eat other consumers.

• Herbivores eat other consumers, while carnivores eat producers.

• Herbivores eat dead organisms, while carnivores make their own food.

Multiple Choice

What would be the most likely long-term consequence for an ecosystem if all decomposers were suddenly removed?

• Consumers would adapt to become producers.

• The soil would become poor as nutrients from dead organisms are not recycled.

• The population of producers would grow uncontrollably.

• Omnivores would have more food choices available.

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Modeling Energy Flow: Food Chains & Webs

Food Chain

• ​A food chain shows a single pathway for energy flow in an ecosystem.

• ​​This is a simple, linear model showing who eats whom, like a fox eating a rabbit.

• ​Each feeding position in this simple sequence is known as a trophic level.

Food Web

• ​A food web is a more realistic model showing many interconnected food chains.

• ​​It represents the complex, multiple pathways through which energy flows in an ecosystem.

• ​Only about 10% of energy is transferred between levels, limiting the size of the web.

Multiple Choice

What is the primary difference between a food chain and a food web?

• A food chain shows a single pathway for energy flow, while a food web shows many interconnected pathways.

• A food chain shows how energy is created, while a food web shows how it is used.

• A food chain involves many different animals, while a food web involves only one.

• A food chain is a more realistic model of an ecosystem than a food web.

Multiple Choice

Why is a food web considered a more realistic model for showing energy flow than a food chain?

• Because it shows that all energy is transferred between levels.

• Because it is a simple, linear model showing who eats whom.

• Because it represents the complex, multiple feeding relationships that actually exist in an ecosystem.

• Because it only includes one type of producer and consumer.

Multiple Choice

What is the most likely consequence of only about 10% of energy being transferred between trophic levels?

• The size of a food web is limited because there is not enough energy to support many levels.

• The number of interconnected food chains in a food web increases.

• Energy flows more efficiently in a single, direct pathway.

• All organisms in the ecosystem will have the same feeding position.

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Antagonistic Interactions: Competition and Predation

Competition

• This occurs when multiple organisms need the same limited resource to survive and reproduce.

• Organisms compete for things like food, water, sunlight, shelter, and mates.

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

Predation

• This is a relationship where a predator hunts and consumes another organism, the prey.

• The predator benefits by gaining energy and nutrients from eating the prey.

• This interaction is a major way energy moves between consumer trophic levels.

Multiple Choice

What is the primary cause of competition among organisms?

• The transfer of energy between trophic levels.

• The natural cooperation between different species.

• The hunting and consuming of one organism by another.

• The need for the same limited resources.

Multiple Choice

How does the interaction of predation differ from competition?

• Competition helps an organism get nutrients, while predation limits resources.

• Predation involves a struggle for resources like water, while competition is about food.

• Predation is a primary way energy moves between consumers, while competition is a struggle for the same resources.

• Predation occurs between species, while competition only occurs within a species.

Multiple Choice

A population of hawks and a population of owls live in the same forest and both hunt mice for food. If a new disease dramatically reduces the mouse population, what is the most likely outcome for the hawks and owls?

• The hawks and owls will stop interacting with each other.

• One of the species will evolve to eat something different immediately.

• The two species will learn to share the remaining mice.

• The competition between the hawks and owls for food will increase.

Close Relationships: Symbiosis

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Mutualism (+/+)

• In this symbiotic relationship, both of the species involved benefit from it.

• A bee gets nectar from a flower to make honey for food.

• The bee helps the flower reproduce by spreading pollen to other flowers.

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Commensalism (+/0)

• One species benefits, while the other is neither helped nor harmed.

• Barnacles attach to a whale to get a ride through the ocean.

• This interaction does not affect the whale in any significant, measurable way.

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Parasitism (+/-)

• One organism, the parasite, benefits by living on or in a host.

• The host organism is harmed by this long-term and close relationship.

• A tick feeding on a dog's blood is an example of parasitism.

Multiple Choice

What is a symbiotic relationship?

• A relationship where one organism hunts another for food.

• A relationship between organisms of the same species living together.

• A short-term interaction where two organisms compete for resources.

• A long-term, close relationship between two different species.

Multiple Choice

How is parasitism different from commensalism?

• In parasitism, one species is harmed; in commensalism, one species is unaffected.

• In parasitism, one species is unaffected; in commensalism, both species are harmed.

• In parasitism, both species benefit; in commensalism, neither benefits.

• In parasitism, both species live together; in commensalism, they live apart.

Multiple Choice

A cleaner shrimp eats parasites and dead skin off a large fish. The shrimp gets a meal, and the fish is cleaned. Which of the following best describes this relationship?

• Parasitism, because the shrimp is living on the fish and eating parts of it.

• Commensalism, because only the shrimp benefits by getting food.

• Mutualism, because both the shrimp and the fish benefit from the interaction.

• A predator-prey relationship, because the shrimp is eating something off the fish.

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Common Misconceptions

Misconception	Correction
A habitat and a niche are the same thing.	​A habitat is where an organism lives; a niche is how it lives and interacts there.

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Summary

• Ecosystems have living (biotic) and non-living (abiotic) parts that interact.

• Energy flows from producers to consumers and is recycled by decomposers.

• Food webs show energy flow, with about 10% moving between trophic levels.

• Interactions include competition, predation, and symbiosis (+/+, +/0, +/-).

Poll

On a scale of 1-4, how confident are you about explaining the different ways organisms interact in an ecosystem?

• 1

• 2

• 3

• 4