Ecosystems

Ecosystems

Middle School

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Learning Objectives

• Define an ecosystem and identify its biotic and abiotic components.

• Describe the roles of producers, consumers, and decomposers in an ecosystem.

• Explain how energy flows through food chains, food webs, and trophic levels.

• Understand the concepts of niche, carrying capacity, and limiting factors.

• Distinguish between an individual, population, and community in 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

All biotic and abiotic factors in an area, and the complex interactions among them.

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Biotic Factor

A living or once-living component of an environment, such as plants, animals, and their remains.

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Abiotic Factor

A non-living physical part of an environment, such as sunlight, temperature, soil, and water.

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Niche

The specific role of a species in its ecosystem, including how it interacts with its environment.

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Food Web

A diagram showing the multiple, intersecting pathways through which energy and matter flow within an ecosystem.

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What is an Ecosystem?

• An ecosystem has all the living (biotic) and non-living (abiotic) parts in an area.

• Biotic factors include all living or once-living things like plants, animals, and fungi.

• Abiotic factors are the non-living parts like sunlight, temperature, water, and air.

• Ecosystems need energy and can vary in size, from a small log to a forest.

Multiple Choice

Which of the following are all abiotic factors of an ecosystem?

• Sunlight, temperature, and soil

• Plants, animals, and fungi

• Water, bacteria, and rocks

• Soil, remains, and temperature

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An Organism's Role and Home

An Organism's Role

• A species' specific role is its niche, including how it gets food and interacts with others.

• Two different species cannot occupy the exact same niche in the same habitat for long.

• One species would eventually outcompete the other for the same resources.

An Organism's Home

• The physical location where a specific population of a species lives is called its habitat.

• Organisms must adapt to their habitat in order to survive and thrive in their environment.

• For example, a wolf's white fur helps it blend into its snowy habitat to hunt.

Multiple Choice

What is the term for the specific role a species plays in its ecosystem, including how it gets food and interacts with its environment?

• Niche

• Habitat

• Trophic Level

• Community

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The Flow of Energy: Producers

Photoautotrophs

• These producers, including plants and algae, capture energy from sunlight to make their own food.

• The process of converting light energy into chemical energy is known as photosynthesis.

• They form the foundation of most food chains on land and in the upper ocean.

Chemoautotrophs

• These producers, like some bacteria, use energy from chemical compounds to make food.

• The process of using chemical energy to produce food is called chemosynthesis.

• They are often found in extreme environments, like deep-sea vents where sunlight cannot reach.

Multiple Choice

What is the primary difference between photoautotrophs and chemoautotrophs?

• Their energy source

• The type of ecosystem they live in

• Whether they are a plant or a bacteria

• Their position in the food chain

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The Flow of Energy: Consumers and Decomposers

Consumers

• Consumers, also known as heterotrophs, get energy by eating other organisms.

• Herbivores eat producers, carnivores eat other animals, and omnivores eat both.

• They are essential for transferring energy from one level to another.

Decomposers

• Decomposers break down the remains of dead organisms and their waste.

• This process releases simple molecules back into the environment for producers.

• Types include scavengers, detritivores, and saprotrophs like fungi and bacteria.

Multiple Choice

Which type of organism gets energy by eating both producers and consumers?

• Omnivore

• Herbivore

• Carnivore

• Detritivore

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Energy Flow in Ecosystems

Food Chain

• A food chain illustrates a single, direct pathway for how energy flows in an ecosystem.

• For example, energy flows from the grass to the grasshopper, and then to the snake.

• It shows a simple and linear sequence of who eats whom in an ecological community.

Food Web

• A food web is more complex, showing many interconnected food chains and feeding relationships.

• It represents the multiple pathways through which energy can flow within an ecosystem.

• This is a more realistic model of how energy is transferred in a real-world environment.

Multiple Choice

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

• A food web shows multiple intersecting pathways of energy flow, while a food chain shows only one.

• A food chain includes decomposers, while a food web does not.

• A food web only shows producers and consumers.

• A food chain shows how all organisms in an ecosystem are connected.

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Trophic Levels and Energy Transfer

• A trophic level is an organism's feeding position in a food chain.

• Only about 10% of energy transfers from one trophic level to the next.

• Most energy is used for life processes or is lost as heat.

• Biomass, the mass of organisms, decreases at higher trophic levels.

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Multiple Choice

Approximately how much energy is transferred from one trophic level to the next?

• 10%

• 100%

• 50%

• 90%

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Levels of Ecological Organization

• An individual is a single living organism, like one deer.

• A population is a group of the same species in an area.

• A community has all populations of species that live and interact together.

• An ecosystem is a community interacting with its abiotic (non-living) environment.

Multiple Choice

What is the term for all the different populations of species living and interacting in the same area?

• Community

• Ecosystem

• Population

• Biosphere

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What Affects Population Size?

• Limiting factors are conditions that control a population's growth.

• Carrying capacity is the maximum population size an environment can support.

• Dense populations are affected more by competition and disease.

• Natural disasters affect populations regardless of their density.

Multiple Choice

What term describes the maximum number of individuals of a species that an ecosystem can sustainably support?

• Carrying capacity

• Limiting factor

• Population density

• Niche

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Common Misconceptions

Misconception	Correction
Food chains are a complete picture of energy flow.	Food chains are simplified models. Food webs are more accurate.
All energy from one trophic level passes to the next.	Only about 10% of energy is transferred between trophic levels.
An ecosystem is just a collection of animals.	An ecosystem includes all biotic (living) and abiotic (non-living) factors.

Multiple Choice

A new disease starts to spread among a dense population of rabbits. Why is this considered a density-dependent limiting factor?

• Because the disease spreads more easily in a dense population.

• Because the disease is an abiotic factor.

• Because the disease affects all populations equally.

• Because only rabbits are affected by the disease.

Multiple Choice

In a forest ecosystem, a wildfire occurs. How would this event, as a density-independent factor, impact the ecosystem's carrying capacity for a deer population?

• It would likely decrease the carrying capacity by reducing food and habitat, regardless of the deer population size.

• It would increase the carrying capacity by creating more open space.

• It would only affect the carrying capacity if the deer population was very large.

• It would have no impact on the ecosystem's carrying capacity for deer.

Multiple Choice

A simple food chain is: Algae -> Fish -> Heron. If a pollutant kills most of the algae, what is the most likely long-term consequence for the heron population?

• The heron population will decrease due to a lack of food (fish).

• The heron population will increase because there are fewer predators.

• The heron population will not be affected at all.

• The herons will switch to eating a different type of producer.

Multiple Choice

If two species of birds that eat the same exact seeds are introduced to an island, what does the Competitive Exclusion Principle predict will happen over time?

• One species will likely outcompete the other, leading to the decline or elimination of the less successful species.

• Both species will thrive and share the resources equally.

• The two species will interbreed to create a new species.

• The birds will decide to eat different types of food to avoid competition.

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Summary

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

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

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

• A species' niche and limiting factors determine a population's carrying capacity.

Poll

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

• 1

• 2

• 3

• 4