Stability and Change in Populations

Stability and Change in Populations

Middle School

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Learning Objectives

• Define an ecosystem and its parts, like populations and communities.

• Explain how resources like food and water affect organism growth and reproduction.

• Describe how organisms interact through competition, predation, and mutualism.

• Analyze how ecosystem disruptions affect the stability of its populations.

Key Vocabulary

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Ecosystem

The community of living organisms interacting with nonliving parts of their environment.

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Population

A group of the same type of organism that is living in the same area.

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Resource

A substance or object in the environment required by an organism for survival.

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Competition

An interaction between organisms that need the same limited resource to survive and grow.

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Stability

When a system stays relatively constant because of balanced inputs and outputs.

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Consumer

An organism that gets energy by feeding on other organisms in the food web.

Key Vocabulary

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Producer

An organism, like a plant, that is able to produce its own food energy from sunlight.

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Decomposer

An organism that breaks down dead organic material, returning important nutrients back to the soil.

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Biodiversity

The variety of different species that are found in the Earth's many diverse ecosystems.

What Is an Ecosystem?

• An ecosystem has living (biotic) and nonliving (abiotic) parts that interact.

• Abiotic factors include sunlight, water, soil, and air temperature.

• A community includes all populations of different species in an area.

Multiple Choice

What is an ecosystem?

• A system where living and nonliving things interact

• A group of animals of the same species

• Only the nonliving parts of an environment

• Only the living organisms in an area

Multiple Choice

Which list includes only abiotic factors that can be found in an ecosystem?

• Sunlight, water, and air temperature

• Plants, animals, and soil

• Water, trees, and fish

• Populations, communities, and soil

Multiple Choice

A scientist studies how the amount of water in a desert affects the different populations of cacti and lizards. Which of the following is the best description of what the scientist is studying and why?

• A community, because it only involves different populations of species.

• An ecosystem, because it includes the interactions between living organisms and their nonliving environment.

• A population, because it focuses on one type of living thing.

• An abiotic factor, because it focuses on the impact of water.

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How Does Energy Move in an Ecosystem?

• Energy flows from one organism to another, as shown in a food web.

• ​Producers, like plants, start the flow by making their own food.

• Consumers get energy storage molecules by eating other organisms.

• Decomposers break down dead material, recycling nutrients for producers.

Multiple Choice

What is the primary way energy moves through an ecosystem?

• It flows from one organism to another.

• It is created only by consumers.

• It stops once it reaches a producer.

• It is recycled by consumers.

Multiple Choice

What is the relationship between producers and consumers in the flow of energy?

• Producers eat other organisms, while consumers break down dead material.

• Producers make their own food, while consumers eat other organisms to get energy.

• Producers get energy from decomposers, while consumers get energy from the sun.

• Producers recycle nutrients, while consumers make their own food.

Multiple Choice

Based on the roles of organisms in an ecosystem, what would most likely happen if decomposers were removed?

• The producers would eventually have fewer nutrients to make food.

• The consumers would have to start making their own food.

• The amount of energy available to producers would increase.

• The dead material would be eaten by consumers instead.

Resource Availability and Population Growth

• Resource availability limits the growth of organisms and their populations.

• Abundant resources, like food and water, can lead to faster population growth.

• Scarce resources become limiting factors and increase competition among organisms.

Multiple Choice

What is the primary role of resource availability in an ecosystem?

• It limits the growth of populations.

• It determines the color of organisms.

• It only affects individual organisms, not populations.

• It eliminates all competition between organisms.

Multiple Choice

What is the likely effect of having abundant resources, such as food and water, on a population?

• The population will grow more quickly.

• The population will decrease in size.

• The organisms will stop needing resources.

• The resources will become scarce immediately.

Multiple Choice

If a long drought reduces the amount of available water in a habitat, what is the most likely outcome for the animal populations living there?

• Competition for water will increase, and population growth will be limited.

• The animals will learn to live without water.

• The population will grow faster to overcome the drought.

• All animals will cooperate to find new water sources.

Interactions Among Organisms

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Competition

• Two or more organisms require the same limited resource like food.

• This interaction is negative for both of the sides involved.

• It constrains their growth and their ability to successfully reproduce.

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Predation

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

• This interaction can directly reduce the number of prey organisms.

• This can help to keep an entire ecosystem in balance.

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Mutually Beneficial

• This is an interaction where two species benefit from each other.

• Their relationship can become so interdependent they can't survive without.

• A bee pollinating a flower is a classic example of this.

Multiple Choice

Which of the following best describes competition between organisms?

• An interaction where one organism hunts and kills another.

• An interaction where both organisms benefit from each other.

• An interaction where organisms require the same limited resources.

• An interaction that helps an entire ecosystem stay in balance.

Multiple Choice

How does the effect of predation on the organisms involved differ from a mutually beneficial relationship?

• Predation is harmful to one organism, while mutually beneficial relationships are helpful to both.

• Predation helps both organisms, while mutually beneficial relationships harm both.

• Predation involves limited resources like food, while mutually beneficial relationships do not.

• Predation only happens between two animals, while mutually beneficial relationships can involve plants.

Multiple Choice

If a predator is completely removed from an ecosystem, what is the most likely consequence for its primary prey species?

• The prey species would form a mutually beneficial relationship with another organism.

• The population of that prey species would likely increase, potentially leading to an imbalance in the ecosystem.

• The prey species would experience more competition for resources.

• The prey species would evolve to no longer need a predator.

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Ecosystem Stability and Change

• Ecosystems are dynamic, meaning their characteristics can vary over time.

• Population stability occurs when births equal the number of deaths.

• Disruptions to an ecosystem can cause shifts in all its populations.

• Biodiversity measures an ecosystem’s ability to resist change and stay healthy.

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Multiple Choice

What does it mean for a population in an ecosystem to be stable?

• The number of births is equal to the number of deaths.

• The ecosystem has a high level of biodiversity.

• The ecosystem never experiences any changes.

• All of the animals in the ecosystem are the same size.

Multiple Choice

What is the relationship between an ecosystem's biodiversity and its ability to resist change?

• Higher biodiversity helps an ecosystem resist change.

• Higher biodiversity makes an ecosystem change more quickly.

• Biodiversity is only important for the number of plants.

• Biodiversity has no effect on how an ecosystem handles change.

Multiple Choice

If a sudden disease significantly reduces a major plant population in an ecosystem, what is the most likely outcome?

• It will cause shifts in the ecosystem's other populations.

• The number of births and deaths will remain equal.

• The ecosystem will become healthier and more stable.

• Only the animal populations that eat that plant will be affected.

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Common Misconceptions

Misconception	Correction
A population can grow forever.	Growth is always limited by factors like food, water, and space.
Ecosystems are static and never change.	Ecosystems are dynamic and constantly changing.
Organisms only compete with each other.	Organisms also have mutually beneficial relationships.
Humans are separate from ecosystems.	Humans are part of ecosystems and our actions impact them.

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Summary

• An ecosystem includes all living (biotic) and nonliving (abiotic) things in an area.

• Energy flows through an ecosystem, while nutrients are recycled within it.

• The availability of resources like food and water limits population size.

• Organisms interact through competition, predation, and mutually beneficial relationships.

• A population’s stability is determined by the balance of births and deaths.

• Disruptions can cause significant shifts in an ecosystem's populations.

Poll

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