Populations And Ecosystems

Populations and Ecosystems

Middle School

​

Learning Objectives

• Use data to explain how resources affect organisms and populations.

• Model how energy flows and matter cycles in an ecosystem.

• Predict interaction patterns like competition, predation, and mutual benefit among organisms.

• Argue how ecosystem changes can affect different populations of organisms.

• Define biodiversity and evaluate solutions for maintaining it for human use.

Key Vocabulary

​

Ecosystem

An ecosystem is a community of living organisms interacting with the non-living parts of their environment.

​

Biotic Factor

A biotic factor is any living or once-living component that affects another organism in an ecosystem.

​

Abiotic Factor

An abiotic factor is any non-living chemical or physical part of the environment that affects organisms.

​

Resource Availability

Resource availability refers to the supply of essential materials that any given organism needs to survive.

​

Competition

Competition is an interaction between organisms that require the same limited resources like food or space.

​

Predation

Predation is a biological interaction where one organism, the predator, hunts and kills another, the prey.

Key Vocabulary

​

Mutualism

A relationship where both organisms benefit from each other in a shared environment.

​

Trophic Level

Each step in a food chain or food web that shows energy transfer.

​

Carrying Capacity

The largest population of a particular species that an area can successfully support over time.

​

Biodiversity

The wide variety of plant and animal life in a particular habitat or ecosystem.

​

Ecosystem Services

The many important benefits that humans receive from healthy and functioning natural ecosystems.

​

Invasive Species

A non-native species that is introduced to a new environment and causes harm.

​

​

What is an Ecosystem?

• An ecosystem is a community of organisms interacting with their physical environment.

• Biotic factors are all the living parts, like plants, animals, and fungi.

• Abiotic factors are non-living things such as sunlight, water, and soil type.

• Organisms get energy as producers, consumers, or decomposers which break down dead matter.

Multiple Choice

Which statement correctly defines the biotic components of an ecosystem?

• The number of consumers in an area determines the amount of rainfall it receives.

• Biotic factors are the animals, and abiotic factors are the plants.

• Biotic factors are the living parts, and abiotic factors are the non-living parts.

• Biotic factors are producers, and abiotic factors are consumers.

Multiple Choice

Deduce the relationship between abiotic and biotic factors in an ecosystem.

• The number of consumers in an area determines the amount of rainfall it receives.

• Biotic factors like plants determine the temperature and soil type of an area.

• Abiotic and biotic factors exist in the same area but do not interact with each other.

• Sunlight, water and soil helps in the growth of plants in an area.

Multiple Choice

If a new factory's pollution blocked out most of the sunlight in an ecosystem, what would be the most likely long-term effect?

• The plant and animal populations would likely decrease due to the loss of a critical abiotic factor.

• The temperature would increase to make up for the lack of sunlight.

• The animals would adapt and learn to live in complete darkness.

• The soil type would change to produce its own light for the plants.

​

​

Energy Flow and Matter Cycling

Energy Flow

• Energy travels in a one-way path through an ecosystem, from producers to consumers.

• The path of energy is described by trophic levels, with each level feeding on the one below it.

• Only about 10% of energy is transferred from one trophic level to the next, creating an energy pyramid.

Matter Cycling

• Matter, in the form of nutrients, is continuously cycled within an ecosystem and is never lost.

• Food webs illustrate how matter moves from producers to consumers and eventually to decomposers.

• Decomposers break down dead organisms, returning essential nutrients back to the environment for producers to use again.

Multiple Choice

What is the primary difference between how energy and matter move through an ecosystem?

• Energy moves in a one-way path, while matter is continuously cycled.

• Matter moves in a one-way path, while energy is continuously cycled.

• Both energy and matter are lost as they move through the ecosystem.

• Both energy and matter are created by producers in an ecosystem.

Multiple Choice

What is the essential role of decomposers in the cycling of matter?

• They create new energy for producers to use.

• They are the main source of food for consumers.

• They break down dead organisms to return nutrients to the environment.

• They convert sunlight into chemical energy for the food web.

Multiple Choice

An energy pyramid illustrates that only about 10% of energy is transferred between trophic levels. Which group of organisms would receive the least amount of the original energy captured by producers?

• The primary consumers, because they get the most energy from producers.

• The secondary consumers, because they are two trophic levels above the producers.

• The decomposers, because they recycle energy from all levels.

• All consumer levels receive the same amount of energy.

​

​

Resource Availability and Population Growth

Abundant Resources

• When resources are plentiful, organisms can easily grow larger and reproduce more successfully.

• This leads to a steady and significant increase in the overall size of the population.

• The ecosystem can support a large and diverse number of organisms living and thriving together.

Scarce Resources

• A lack of resources limits the growth and reproductive success of organisms in an area.

• This scarcity often causes the overall size of the population to decrease over time.

• The limited availability of resources is a primary driver of competition among different organisms.

Multiple Choice

What is the primary factor that determines whether a population will increase or decrease in size?

• The availability of resources

• The number of predators in the area

• The size of the individual organisms

• The climate of the ecosystem

Multiple Choice

How does a scarcity of resources typically affect an ecosystem?

• It helps organisms grow larger and reproduce more.

• It leads to increased competition and a smaller population.

• It allows the ecosystem to support a more diverse population.

• It causes organisms to stop growing entirely.

Multiple Choice

A forest fire clears a large area, but a year later, new grasses and shrubs grow in abundance. What is the most likely effect on the local deer population that eats these plants?

• The deer population will likely increase because of the abundance of food.

• The deer population will likely decrease because of increased competition.

• The deer population will stay exactly the same.

• The deer will grow larger, but the population size will not change.

Factors Limiting Populations

• A limiting factor is anything that restricts a population's size.

• These can be living (biotic) or non-living (abiotic) factors.

• These factors determine an ecosystem's carrying capacity for a species.

Multiple Choice

What is the primary function of a limiting factor?

• To restrict a population's size.

• To help a population grow larger.

• To encourage new species to enter an area.

• To change an ecosystem's climate.

Multiple Choice

What is the relationship between limiting factors and an ecosystem's carrying capacity?

• They determine the maximum population size an ecosystem can support.

• They increase the number of resources available in an ecosystem.

• They have no effect on the maximum population size an ecosystem can support.

• They only include the living parts of an ecosystem.

Multiple Choice

A severe drought, a non-living factor, causes most of the plants in a deer habitat to die. What is the most likely impact on the ecosystem?

• The carrying capacity for deer will decrease due to a lack of food.

• The carrying capacity for deer will increase because there are fewer plants.

• Only the non-living (abiotic) factors in the ecosystem will change.

• The deer population will be unaffected by changes in plant life.

Interactions Among Organisms

​

Competition

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

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

• Competition is a struggle for survival among organisms in an ecosystem.

​

Predation

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

• This interaction helps control the population size of the prey species.

• Predators have adaptations like sharp teeth to help them hunt effectively.

​

Mutualism

• This is a close relationship where two different species help each other.

• Both of the organisms benefit from this important type of interaction.

• Sometimes one species cannot survive without its partner in this relationship.

Multiple Choice

Which statement best defines the interactions among organisms in an ecosystem?

• The way organisms grow from birth to adulthood.

• The different ways organisms affect each other to survive.

• The process by which plants make their own food.

• The movement of animals from one region to another.

Multiple Choice

What is a key difference between mutualism and predation?

• In mutualism, both species benefit, while in predation, only one does.

• Mutualism occurs between members of the same species, but predation does not.

• Predation helps control population size, but mutualism does not.

• Both interactions are struggles for the same limited resources.

Multiple Choice

If a major predator is removed from an ecosystem, what is the most likely long-term effect on its prey's population?

• The prey population would likely increase due to the lack of a predator.

• The prey would evolve new adaptations like sharp teeth.

• The prey population would find a new mutualistic partner.

• The prey would have fewer resources like food and water.

​

​

Ecosystems are Always Changing

• Ecosystems are dynamic, meaning their characteristics naturally change over time.

• Disruptions are events like fires or new diseases that change an ecosystem.

• A change to one part of an ecosystem can affect all populations.

• A small change, like removing a predator, can cause large shifts.

​

Multiple Choice

What does it mean for an ecosystem to be described as dynamic?

• Their characteristics naturally change over time.

• They are always perfectly stable and balanced.

• They are not affected by events like fires.

• They only contain plants and no animals.

Multiple Choice

What is the relationship between a disruption, like a new disease, and the populations within an ecosystem?

• It can cause changes that impact all populations in the ecosystem.

• It only affects the specific part of the ecosystem where it occurred.

• It makes the ecosystem more stable and less likely to change.

• It has no real effect on the ecosystem's populations.

Multiple Choice

If a disease suddenly removes a major predator of mice from an ecosystem, what is a likely consequence?

• The mouse population will likely increase.

• The populations of plants that the mice eat might increase significantly.

• The ecosystem will stop changing and become stable.

• There will be no noticeable changes to the ecosystem.

​

​

Biodiversity and Ecosystem Services

Biodiversity

• ​Biodiversity refers to the variety of all living species that are found in a particular ecosystem.

• ​​It is often used as a primary measure of the overall health and resilience of an ecosystem.

• ​Greater biodiversity helps ensure that an ecosystem can better withstand and recover from various disasters.

Ecosystem Services

• ​These are the many essential benefits that human beings receive from healthy and thriving ecosystems.

• ​​Key services include water purification, nutrient recycling, soil erosion prevention, food, energy, and medicines.

• ​A decline in biodiversity can negatively impact these services, affecting human well-being and survival.

Multiple Choice

Which statement best defines an ecosystem's biodiversity?

• The variety of all living species in a particular ecosystem.

• The benefits that humans receive from healthy ecosystems.

• The process of recycling nutrients within an environment.

• The overall temperature and weather in a specific region.

Multiple Choice

What is the relationship between an ecosystem's biodiversity and the ecosystem services it provides?

• A decrease in the variety of species can lead to a reduction in the benefits humans receive.

• The number of species in an ecosystem is not related to the benefits humans receive.

• An increase in the variety of species causes a decrease in benefits like clean water.

• Only ecosystems with low biodiversity provide benefits to humans.

Multiple Choice

If a forest ecosystem with high biodiversity loses several of its plant species due to a new disease, what is the most likely consequence?

• The ecosystem will be less resilient and less able to provide key services like food and water purification.

• The ecosystem will recover quickly as other species will easily replace those that were lost.

• The loss of some species will have no impact on the overall health and stability of the ecosystem.

• The services the ecosystem provides will increase to make up for the loss of species.

​

​

What Are Invasive Species?

• An invasive species is a non-native organism that harms its new environment.

• They thrive due to a lack of natural predators, diseases, or competitors.

• Gray squirrels in Britain outcompete native red squirrels for food and habitat.

• The brown tree snake in Guam has wiped out most native bird species.

​

Multiple Choice

What is the definition of an invasive species?

• A non-native organism that causes harm to its new environment.

• Any organism that is introduced to a new area.

• A native species that is struggling to survive.

• An organism that helps other species in an environment.

Multiple Choice

What is the primary reason invasive species are able to thrive in a new environment?

• They are always larger than the native species.

• They often have no natural predators or competitors in the new habitat.

• They are better at hiding from all other animals.

• They can change the weather of the new environment.

Multiple Choice

Based on the provided examples, what is a logical prediction of what happens when an invasive species is introduced into an ecosystem?

• The population of native species may decline due to competition or predation.

• The invasive species will likely not find enough food to survive.

• The native species will quickly adapt to the new arrival.

• The overall biodiversity of the environment will increase.

​

Common Misconceptions About Ecosystems

Misconception	Correction
Energy is recycled within an ecosystem.	Matter is recycled, but energy flows in one direction and is not reused.
An ecosystem is static and unchanging.	Ecosystems are dynamic and constantly changing over time.
All non-native species are harmful.	A non-native species is only 'invasive' if it causes negative ecological or economic impacts.
A bigger animal is always at a higher trophic level.	Trophic level is determined by diet, not size.

​

Summary

• Ecosystems consist of interacting biotic (living) and abiotic (non-living) factors.

• Energy flows one way, while matter is cycled within the ecosystem.

• Limiting factors and resources determine an ecosystem's carrying capacity.

• Biodiversity is a measure of ecosystem health and provides critical services.

Poll

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

• 1

• 2

• 3

• 4