Interactions in Ecosystems

Interactions in Ecosystems

Middle School

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Learning Objectives

• Define biotic and abiotic factors and the levels of ecological organization.

• Describe key species interactions like competition, predation, and symbiosis.

• Explain how energy flows through ecosystems using food chains, webs, and pyramids.

• Analyze how limiting factors and species roles affect population size and ecosystems.

Key Vocabulary

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Habitat

The natural home or environment where an organism, plant, or animal lives and grows.

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Niche

An organism's specific role in its ecosystem, including its diet, activity, and overall behavior.

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Competition

The struggle between organisms for the same limited resources like food, water, or territory.

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Symbiosis

A long-term relationship where two different species live closely together in a biological interaction.

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Producer

An organism that creates its own food, typically through photosynthesis, forming the base of a food web.

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Carrying Capacity

The maximum population size of a species that the environment can sustainably support over time.

Key Vocabulary

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Keystone Species

A species that has a disproportionately large effect on its environment relative to its abundance.

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Invasive Species

A non-native organism that causes ecological or economic harm in its new environment.

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Trophic Cascade

The indirect effect that a change in one species' population has on other trophic levels.

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The Parts of an Ecosystem

Ecosystem Components

• Abiotic factors are the nonliving parts of an ecosystem, such as sunlight, water, and temperature.

• Biotic factors are all the living or once-living parts of an ecosystem, like plants and animals.

• These parts interact with each other to create a complete and functioning ecosystem.

Levels of Organization

• Life is studied in levels, beginning with an individual organism and then a whole population.

• Different populations that live together in the same area form what is known as a community.

• An ecosystem is the community of organisms combined with the nonliving factors of their environment.

Multiple Choice

What best defines an ecosystem?

• A community of organisms combined with their nonliving environment.

• All the living or once-living parts of an environment.

• A group of different populations that live together in the same area.

• The nonliving factors in an environment, such as sunlight and water.

Multiple Choice

What is the primary difference between the biotic and abiotic factors of an ecosystem?

• Biotic factors are animals, while abiotic factors are plants.

• Biotic factors are living or once-living, while abiotic factors are nonliving.

• Biotic factors are the environment's water and temperature.

• Biotic factors are found on land, while abiotic factors are in water.

Multiple Choice

A scientist is studying several populations of plants and animals that live together in the same area. To study this as a complete ecosystem, what else must the scientist include in their study?

• The nonliving factors, such as the area's sunlight and water.

• The total number of organisms in the different populations.

• Another population of animals, such as a pride of lions.

• A single organism, such as one specific elephant.

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Habitat, Niche, and Competition

Habitat vs. Niche

• A habitat is the address where an organism lives, finding its food, shelter, and mates.

• A niche is an organism's role in its habitat, like its profession or what it eats.

• No two species can share the exact same niche in the same habitat for long.

Competition

• This occurs when organisms need the same limited resource, like food, water, or space.

• Intraspecific competition happens between members of the same species, like two male deer locking antlers.

• Interspecific competition is between different species, like birds eating insects from different parts of a tree.

Multiple Choice

What is the primary difference between an organism's habitat and its niche?

• A habitat is its role, while a niche is its address.

• A habitat is its address, while a niche is its role in that environment.

• A habitat only includes living factors, while a niche includes non-living factors.

• A habitat is for a single organism, while a niche is for a whole population.

Multiple Choice

Which of the following scenarios is the best example of intraspecific competition?

• A lion hunting a zebra for food.

• Two squirrels trying to get the same nut.

• A hawk and an owl hunting mice in the same field.

• Different species of birds eating insects from different parts of a tree.

Multiple Choice

If a new species of bird that eats the same insects as a native bird species is introduced to a forest, what is the most likely long-term outcome?

• The two bird species will learn to share the insects equally.

• One species will likely be out-competed and have to find a new food source or habitat.

• Both species will evolve to have different beak shapes immediately.

• The insect population will increase because there are more predators.

Types of Symbiosis: A Close Look

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Mutualism (+/+)

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

• This is a partnership where each organism gains something positive.

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

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Commensalism (+/0)

• One organism benefits from the relationship, and the other is unaffected.

• The second organism does not get harmed or helped in any way.

• Barnacles on a whale get a safe home and a free ride.

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Parasitism (+/-)

• One organism, the parasite, benefits by harming the other organism.

• The other organism, known as the host, is negatively affected.

• A tick feeding on a dog is a common example of this.

Multiple Choice

Which type of symbiotic relationship is defined as a partnership where both of the involved species benefit?

• Mutualism

• Commensalism

• Parasitism

• Competition

Multiple Choice

What is the primary difference between parasitism and commensalism?

• In parasitism one organism is harmed, while in commensalism one is unaffected.

• In parasitism both organisms benefit, while in commensalism only one benefits.

• Parasitism involves a parasite and a host, while commensalism involves two equal partners.

• Parasitism is a long-term relationship, while commensalism is always short-term.

Multiple Choice

A bird builds its nest in a tree, providing a safe home for its young. The tree is not damaged or helped by the bird's nest. What term best describes this relationship?

• Commensalism

• Mutualism

• Parasitism

• Competition

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Energy Flow in Ecosystems

Food Chains and Webs

• Energy flows from producers, like plants, to consumers that eat other organisms.

• Decomposers break down dead matter, returning nutrients to the system for producers to use.

• A food web shows many interconnected food chains and the different pathways for energy flow.

Energy Pyramids

• Organisms use most energy for life processes, and much of this energy is lost as heat.

• The "10% Rule" states that only about 10% of energy moves to the next level.

• This energy loss limits the number of trophic levels that an ecosystem can support.

Multiple Choice

What is the primary role of producers, such as plants, in the flow of energy through an ecosystem?

• To break down dead material and recycle nutrients.

• To consume other organisms to gain energy.

• To provide the initial source of energy for a food chain.

• To transfer energy between many different food chains.

Multiple Choice

What is the main reason that only about 10% of the energy from one trophic level is passed on to the next level?

• The energy is lost because consumers only eat parts of organisms.

• Decomposers absorb most of the energy from the ecosystem.

• Organisms use most of the energy for life processes, and much is lost as heat.

• The energy is not compatible with the organisms at the next level.

Multiple Choice

Considering the significant loss of energy at each step, what is the most logical consequence for the structure of a food web?

• The organisms at the highest trophic levels would become the most numerous.

• The number of potential trophic levels in a food web would be limited.

• Food chains in the ecosystem would extend indefinitely.

• Decomposers would have more energy to recycle as nutrients.

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Understanding Population Dynamics

• Limiting factors are resources like food and water that restrict population growth.

• Carrying capacity is the maximum population size a habitat can sustainably support.

• A population increases from births and when individuals move in (immigration).

• A population decreases from deaths and when individuals move out (emigration).

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Multiple Choice

What is the carrying capacity of a habitat?

• The maximum population size a habitat can sustainably support.

• The initial number of individuals that start a population.

• The speed at which a population grows each year.

• The total number of individuals that have ever lived in a habitat.

Multiple Choice

Which combination of factors would cause a population to increase?

• An increase in births and individuals moving into the area.

• An increase in deaths and individuals moving out of the area.

• A decrease in births and an increase in deaths.

• A decrease in individuals moving in and an increase in individuals moving out.

Multiple Choice

If a population grows larger than its habitat's carrying capacity, what is the most likely outcome?

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

• The population will continue to grow at an even faster rate.

• The habitat's carrying capacity will automatically increase to support the population.

• The individuals in the population will no longer need limiting factors.

Ecosystem Change: Keystone Species and Succession

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Keystone Species

• A keystone species has a large effect on its ecosystem.

• It helps maintain the structure and balance of a biological community.

• Sea otters are a keystone species because they eat sea urchins.

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Trophic Cascade

• Removing a keystone species can trigger a series of cascading changes.

• This chain reaction ripples through the different levels of a food web.

• Without otters, urchins would multiply and destroy the entire kelp forest.

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Ecosystem Succession

• Succession is how ecosystems recover from disturbances like fires or storms.

• Primary succession occurs on new, bare surfaces that do not have soil.

• Secondary succession happens in an area where soil is already present.

Multiple Choice

What is the primary role of a keystone species in its ecosystem?

• To be the most common animal in an ecosystem.

• To help maintain the structure and balance of a biological community.

• To compete with all other species for food.

• To create new, bare surfaces for plants to grow.

Multiple Choice

How does primary succession differ from secondary succession?

• Primary succession happens after fires, while secondary succession happens after storms.

• Primary succession involves animals, while secondary succession only involves plants.

• Primary succession is a fast process, while secondary succession is a very slow process.

• Primary succession begins on surfaces without soil, while secondary succession occurs where soil is already present.

Multiple Choice

Based on the relationships described, what would most likely happen in the ecosystem if sea otters were removed?

• The kelp forest would become healthier and larger.

• The sea urchin population would grow, which would then destroy the kelp forest.

• The ecosystem would be replaced by a different type of forest.

• The sea urchin population would shrink, allowing the kelp to grow.

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Human Influence on Ecosystems

• Invasive species are non-native organisms that can harm ecosystems by outcompeting native species.

• Human activities like development and pollution can cause habitat loss for many species.

• Overfishing and climate change also disrupt the natural balance within an ecosystem.

• We can help by protecting habitats, reducing pollution, and planting native species.

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Multiple Choice

What is an invasive species?

• A non-native organism that can harm an ecosystem.

• A native organism that is considered endangered.

• A species that helps to create balance in an ecosystem.

• An organism that has recently lost its natural habitat.

Multiple Choice

What is the relationship between human activities like development and pollution and an ecosystem?

• The loss of habitat for many species.

• An increase in the number of native species.

• The creation of entirely new ecosystems.

• A sharp decrease in pollution levels.

Multiple Choice

An ecosystem is being damaged by non-native plants that are taking resources away from the native plants. Which action would be the most effective way to help this ecosystem recover?

• Begin a project to remove the invasive plants and re-plant native ones.

• Introduce a new, non-native animal to eat the invasive plants.

• Start a fishing program to see how the fish have been affected.

• Build a fence around the ecosystem to prevent further damage.

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Common Misconceptions

Misconception	Correction
A habitat is the same as a niche.	A habitat is an organism's address. A niche is its job or role.
Food chains are a realistic model of energy flow.	Real ecosystems have complex food webs, not simple food chains.
Removing one species only affects its direct predator.	Removing a species can impact many species across the entire food web.
All non-native species are invasive.	Invasive species are non-native species that cause harm to the ecosystem.

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Summary

• An ecosystem includes both biotic (living) and abiotic (nonliving) factors.

• Every organism has a habitat (where it lives) and a niche (its role).

• Species interact through competition, predation, and symbiosis.

• Energy flows from producers to consumers, with only about 10% moving to the next level.

• Population size is limited by carrying capacity and resource availability.

• Keystone species, invasive species, and human activities can harm ecosystems.

Poll

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

• 1 (Not confident)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)