Populations, Communities, and Ecosystems

Populations, Communities, and Ecosystems

Middle School

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Learning Objectives

• Define the levels of organization in an ecosystem, from organism to community.

• Explain key interactions between organisms like competition, predation, and symbiosis.

• Trace how energy flows through an ecosystem using food webs and energy pyramids.

• Describe how limiting factors and keystone species can affect different populations.

• Distinguish between the different categories of ecosystem services and their importance.

Key Vocabulary

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Abiotic Factor

A nonliving part of an ecosystem that shapes its environment and influences the organisms living there.

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Biotic Factor

A living component of an ecosystem, including organisms like plants, animals, fungi, and even tiny bacteria.

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Niche

An organism's special role within its ecosystem, which includes what it eats and how it survives.

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Competition

The struggle between different organisms to use the same limited resources, such as food or space.

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Symbiosis

A close, long-term relationship where two different species live together in direct and intimate contact.

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Carrying Capacity

The largest population size that a specific environment can sustainably support over a long period of time.

Key Vocabulary

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Keystone Species

A species that has a very large effect on its ecosystem compared to its population size.

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Succession

The process of gradual change in the community of an ecosystem over a long period of time.

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Ecosystem Services

The many different benefits that healthy ecosystems provide to humans in their everyday lives.

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Resilience

The ability of an ecosystem to recover from disturbances and still maintain its essential functions.

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Levels of Organization

• Abiotic factors are the nonliving parts of an ecosystem, like sunlight and water.

• Biotic factors are all the living or once-living organisms in the ecosystem.

• An individual is an organism; a group of the same species is a population.

• Populations form a community, which with abiotic factors, makes an ecosystem.

Multiple Choice

Which list shows the levels of organization from the simplest to the most complex?

• Organism, Population, Community

• Community, Population, Organism

• Population, Organism, Community

• Ecosystem, Community, Population

Multiple Choice

What is the key difference between biotic and abiotic factors within an ecosystem?

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

• Abiotic factors include plants and animals, while biotic factors include water and soil.

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

• Abiotic factors are the predators, while biotic factors are the prey.

Multiple Choice

A scientist is studying a forest community, which includes populations of deer, birds, and trees. To expand the study to the entire ecosystem, what must be included?

• The nonliving factors and all other populations in the area.

• Only the other animal populations that interact with the deer.

• A single deer organism to study its individual features.

• The climate data from a different type of ecosystem.

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Habitat, Niche, and Competition

• An organism's habitat is its address, which is the place where it lives.

• An organism's niche is its profession, including what it eats and its role.

• Intraspecific competition occurs between members of the same species, like two oak trees.

• Interspecific competition occurs between different species, such as grasses and weeds.

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Multiple Choice

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

• A habitat is the place where an organism lives, while its niche is its specific role or job in that place.

• A habitat is an organism's role, while its niche is the specific place where it lives.

• A habitat describes what an organism eats, while a niche describes where it finds shelter.

• A habitat is for animals only, while a niche is for plants only.

Multiple Choice

Which of the following is a clear example of intraspecific competition?

• Competition between two oak trees for sunlight.

• Competition between grasses and weeds for space.

• Competition between a lion and a hyena for food.

• Competition between a bee and a flower.

Multiple Choice

Which scenario describes interspecific competition occurring within a shared habitat?

• Two different bird species trying to build nests in the same tree.

• Two squirrels from the same family gathering nuts from the same tree.

• A single tree growing taller to get more sunlight.

• A predator hunting its prey.

Types of Symbiosis

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Mutualism (+/+)

• Both of the species involved in this relationship benefit from it.

• For example, bees get nectar from flowers while pollinating them.

• This is a win-win relationship for both organisms involved.

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Commensalism (+/0)

• One species benefits, while the other is not affected at all.

• Barnacles ride on whales to find new sources of food.

• The whale is neither helped nor harmed by the barnacles.

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Parasitism (+/-)

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

• The organism that is harmed by the parasite is the host.

• A tick feeding on the blood of a dog is an example.

Multiple Choice

What is mutualism?

• A relationship where both of the species involved benefit.

• A relationship where one species benefits and the other is harmed.

• A relationship where one species benefits and the other is unaffected.

• A relationship where both species are harmed.

Multiple Choice

What is the primary difference between parasitism and commensalism?

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

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

• In parasitism one organism is the host, while in commensalism there is no host.

• In parasitism both organisms are harmed, while in commensalism neither is harmed.

Multiple Choice

A mosquito feeds on a human's blood to get a meal. The human is harmed because they lose blood and can be exposed to disease. Which statement best explains this relationship?

• This is an example of parasitism because the mosquito (parasite) benefits by feeding on the human (host), who is harmed.

• This is an example of mutualism because the mosquito gets food and the human gets a bite.

• This is an example of commensalism because the mosquito benefits and the human is not affected.

• This is an example of competition because both the mosquito and the human are harmed.

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Energy Flow in Ecosystems

• Energy flows in one direction, from producers to consumers and finally to decomposers.

• A food web shows the many interconnected food chains in an ecosystem.

• An energy pyramid shows how energy decreases at each feeding level.

• Only about 10% of energy is transferred to the next level up.

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Multiple Choice

What is the primary direction of energy flow within an ecosystem?

• From producers to consumers

• From consumers to producers

• In a continuous cycle between all organisms

• From decomposers to producers

Multiple Choice

What is the main purpose of using an energy pyramid to model an ecosystem?

• It shows that the amount of available energy decreases at each level.

• It shows the specific pathways in a single food chain.

• It shows that the number of organisms increases at higher levels.

• It shows how energy is recycled back to producers.

Multiple Choice

If the producers in a food chain contain 10,000 units of energy, approximately how much energy is transferred to the secondary consumers?

• 1,000 units

• 100 units

• 10,000 units

• 9,000 units

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Population Growth and Carrying Capacity

Limiting Factors

• Population growth is restricted by a resource or condition in short supply, called a limiting factor.

• Common limiting factors include food, water, and the amount of available space for shelter and living.

• Environmental conditions like temperature and the presence of diseases can also limit population size.

Carrying Capacity

• Carrying capacity is the largest population size that an environment can support over a long period.

• As a population approaches its carrying capacity, the growth rate starts to slow down significantly.

• Population size balances increases from births with decreases from deaths in the habitat.

Multiple Choice

What is the carrying capacity of an environment?

• The starting size of a new population.

• The largest population size an environment can consistently support.

• The rate at which a population increases.

• The total number of births in a single year.

Multiple Choice

What is the primary role of limiting factors like food, water, and space in an ecosystem?

• They only affect the number of births.

• They restrict how large a population can grow.

• They help a population grow indefinitely.

• They are only present in large populations.

Multiple Choice

What is the most likely outcome for a population as it approaches its environment's carrying capacity?

• The population's growth rate will speed up.

• The number of available resources will increase.

• The population's growth rate will slow down as resources become scarce.

• The balance of births and deaths will not be affected.

Ecosystem Change and Stability

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Keystone Species

• A keystone species has a huge impact on its entire ecosystem.

• Sea otters control sea urchins, which protects vital kelp forests.

• Removing them can cause dramatic changes throughout the entire food web.

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Invasive Species

• An invasive species is a non-native organism that harms an ecosystem.

• They spread quickly and outcompete native species for essential resources.

• This is often because they lack natural predators in the new environment.

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Ecological Succession

• Succession is the gradual process of community change over long periods.

• Primary succession starts slowly on bare rock with absolutely no soil.

• Secondary succession is faster as it begins where soil already exists.

Multiple Choice

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

• It is a non-native species that harms the environment.

• It is the first organism to grow on bare rock.

• It has a disproportionately large effect on its ecosystem.

• It is a species that starts the process of secondary succession.

Multiple Choice

How does primary succession differ from secondary succession?

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

• Secondary succession involves invasive species, while primary succession involves keystone species.

• Primary succession happens in established communities, while secondary succession creates new ones.

• Secondary succession begins on existing soil, while primary succession begins on bare rock.

Multiple Choice

A population of rabbits is introduced to a grassland ecosystem where they have no natural predators. Based on the principles of ecosystem change, what is the most likely long-term consequence?

• The rabbits would become a keystone species, helping to stabilize the ecosystem.

• The ecosystem would undergo primary succession, starting with bare rock.

• The rabbits would outcompete native species for resources, disrupting the food web.

• The native predators would quickly learn to hunt the new rabbits.

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Ecosystem Services: Nature's Benefits

• Provisioning services are the tangible goods we get from nature, such as food and water.

• Regulating services are processes that keep the environment stable, like water filtration and flood control.

• Cultural services are non-material benefits that enrich our lives, including recreation and inspiration.

• Supporting services are basic processes like photosynthesis that enable all other services.

Multiple Choice

Which category of ecosystem services includes goods taken directly from nature, such as food and timber?

• Provisioning services

• Regulating services

• Cultural services

• Supporting services

Multiple Choice

What is the key difference between regulating services and supporting services?

• Regulating services control natural processes, while supporting services are the processes that enable all other services.

• Regulating services are material goods, while supporting services are non-material benefits.

• Regulating services provide recreational opportunities, while supporting services create goods like timber.

• Regulating services involve artistic inspiration, while supporting services involve water filtration.

Multiple Choice

A coastal mangrove forest protects a town from storm surges and provides a beautiful location for residents to go kayaking. Which two types of ecosystem services are being provided?

• Regulating and Cultural

• Provisioning and Supporting

• Cultural and Provisioning

• Supporting and Regulating

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Common Misconceptions

Misconception	Correction
A habitat is the same as a niche.	A habitat is an organism's address, while a niche is its role.
Energy is recycled within an ecosystem.	Nutrients are recycled, but energy flows in one direction and is lost.
A population can grow forever.	Carrying capacity limits how large a population can become.
Ecosystems are static and unchanging.	Ecosystems are dynamic and constantly change over time.

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Summary

• Ecosystems are organized into levels: organism, population, community, and ecosystem.

• Organisms interact through competition, predation, and different types of symbiosis.

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

• A population’s maximum size is determined by limiting factors and carrying capacity.

• Keystone species maintain ecosystem stability, while invasive species can cause harm.

• Healthy ecosystems provide essential services that support life on Earth.

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)