Communities and ecosystems

A community is all the populations of different species living and interacting in the same area.

A community is all the different species living together in the same area. For example, fish, plants, insects, and bacteria living in a pond.

A community is all the different species living together in the same place.

An ecosystem is a community of living things and the non-living environment they interact with.

An ecosystem is a community of organisms interacting with the abiotic environment.

An ecosystem includes living organisms and the non-living environment. For example, a forest with trees, animals, soil, sunlight, and rain.

A community includes only living things. An ecosystem includes living things plus abiotic (non-living) factors such as water, soil, light, and temperature.

No. A community includes only living organisms.

All the animals and plants in a coral reef community, without including the water or sunlight.

Sunlight warming a lake, soil nutrients in a forest, or water temperature in the ocean.

Yes. An ecosystem includes non-living factors such as water, sunlight, soil, and temperature.

Abiotic means non-living parts of the environment, such as sunlight, temperature, water, soil, and rocks.

Abiotic means non-living parts of the environment.

Biotic means living components of an environment, such as plants, animals, fungi, and microorganisms.

Trees in a forest, fish in a lake, grass in a field, or bacteria in soil.

A population is a group of individuals of the same species living in the same area at the same time.

Biotic means living parts of the environment.

A habitat is where an organism lives. For example, a frog living in a pond or a bird nesting in a tree.

A lake ecosystem where sunlight enters, rain adds water, and fish and nutrients move in and out.

Examples include predation, competition, parasitism, mutualism, or herbivory between different species in the same area.

A habitat is the place where an organism lives.

Because energy and matter can move in and out of the ecosystem.

Ecosystem, because temperature and rainfall are abiotic (non-living) factors.

Energy enters as sunlight, moves to plants, then to animals, and is lost as heat. For example, Sun → grass → rabbit → fox.

Energy enters ecosystems mainly as sunlight.

Dead plants and animals decompose and nutrients return to the soil, where plants reuse them.

A habitat is the place where an organism lives and finds the resources it needs to survive.

No. Energy flows through ecosystems and is lost as heat.

Ecosystem, because it includes living organisms plus non-living factors like soil, air, and sunlight.

A habitat is where a particular species lives. An ecosystem includes many species plus abiotic factors and their interactions.

Yes. Matter such as nutrients and water is recycled.

An open system is a system where both energy and matter can enter and leave across the system boundary.

Because energy (sunlight, heat) and matter (water, nutrients, organisms) move in and out of the ecosystem.

Scale is the size or level at which a system is studied, such as a pond, a forest, a biome, or the whole planet.

At small scale you see local interactions. At large scale you see wider patterns and flows across regions.

Community = only living things (different populations of different species in the same area).

Ecosystem = community + abiotic environment interacting together.

Sustainability means using resources at a rate they can be replaced, so the ecosystem can keep going in the future.

Sustainability is using resources at a rate that allows them to be replaced so the system can continue long term.

A disturbance is an event that disrupts ecosystem structure or function and changes populations or resource flows.

A storage is a place where energy or matter is held for a period of time within a system.

Redundancy is when multiple species perform similar roles, so ecosystem functions continue if one species is lost.

Low biodiversity and small storages reduce the ability to recover after disturbance.

Sustainability is long-term continued functioning; resilience is ability to recover after disturbance.

Sustainable fishing means catching only as many fish as can be replaced by reproduction each year.

If one species declines, others can replace its role, reducing the chance of function collapse.

High biodiversity, large storages, and redundancy (multiple species doing similar roles).

Resilience is the ability of an ecosystem to resist disturbance and recover after it.

Natural: wildfire, storm, flood, drought. Human: deforestation, pollution, overfishing, oil spill.

With little buffering and few backups, disturbances push the system past thresholds more easily.

Large storages buffer change by releasing resources slowly, reducing extremes after disturbance.

Bees, flies, butterflies and beetles can all pollinate; if one declines, others may still pollinate many plants.

Cutting down forest faster than it can regrow is unsustainable because the resource gets depleted.

Disturbance causes change; resilience determines recovery; recovery shows how fast the system returns towards its previous state.

More biodiversity creates more pathways and backup species, so ecosystem functions continue even if one species declines.

Forests and soils store carbon in biomass and organic matter, reducing rapid carbon release to the atmosphere.

Coral reefs under repeated heat stress can shift to algal-dominated states and recover slowly or not at all.

Changes are more extreme because there is little buffering; recovery is slower and collapse risk is higher.

Resource use does not exceed renewal, so ecosystem functions and services continue over time.

Redundancy.

Habitat destruction, pollution, overexploitation, and invasive species can reduce resilience by simplifying the ecosystem.

Resilience is how well an ecosystem can recover after a disturbance and keep functioning.

Wetlands and lakes store water, reducing floods and providing water during dry periods.

After a disturbance, a resilient ecosystem recovers faster and is more likely to maintain key functions and services.

High biodiversity often increases redundancy because more species means more chances that roles overlap.

A tipping point is a threshold where small extra change causes a large shift to a new state that may be hard to reverse.

Resilience.

After a fire, plants regrow and animals return over time. The ecosystem returns to a working state.

Increase biodiversity, protect or restore storages (forests, wetlands, soils), and reduce chronic human pressures.

Sustainability is long-term continued functioning; resilience is short-term ability to recover after disturbance.

No. Redundancy protects function, but losing species still reduces biodiversity and can weaken the system over time.

Maintaining storages prevents rapid depletion, keeping ecosystem services available for the long term.

A disturbance is an event that disrupts an ecosystem. Natural: hurricane or fire. Human: oil spill or deforestation.

More species means more “backup” organisms. If one species declines, others can still keep ecosystem jobs going.

If bees decline, other pollinators like butterflies, flies, and beetles can still pollinate many plants.

A storage is a place where a resource is kept in an ecosystem, like water in a wetland or carbon in a forest.

Wetlands store extra water during heavy rain, so less water rushes downstream at once.

Forests store carbon in tree biomass and in soils, which slows how fast carbon enters the atmosphere.

Redundancy means several species do the same job, so the system still works if one species is lost.

Dead leaves can be broken down by fungi, bacteria, earthworms, and beetles. If one is missing, others still decompose.

Low biodiversity and small storages reduce resilience. Heavy human pressure (pollution, habitat loss) also lowers resilience.

A tipping point is a point where a small extra change causes a big shift, and the ecosystem may not return to the old state.

Biodiversity gives more species. Redundancy gives backup species doing the same job. Storages provide reserves (water/carbon/nutrients). Together they help the ecosystem recover after disturbance.

A keystone species is a species with a disproportionately large effect on ecosystem structure or function relative to its abundance.

A trophic cascade is a chain reaction of population changes through a food web after a species is added or removed.

An ecosystem engineer is a species that modifies the physical environment and creates or maintains habitats for other species.

Keystone species.

They help maintain food-web balance by controlling populations or supporting key interactions, which keeps biodiversity higher.

Because habitat changes can affect many other populations, increasing biodiversity and altering community structure.

Trophic cascade.

Herbivore numbers can increase, plant biomass can decrease, and biodiversity may fall as habitats become simplified.

Beavers build dams that create wetlands, increasing habitat for fish, birds, insects and plants.

If removing one species causes major changes across many other species (food web shifts, biodiversity drops), it is likely a keystone species.

They control dominant populations and maintain habitat/food-web structure, allowing more species to coexist.

Food-web links weaken and key functions fail, so the ecosystem is less able to recover after disturbance.

Step 1: remove keystone → immediate population change. Step 2: knock-on effects spread → community structure and biodiversity change.

State the keystone has a large effect, then describe knock-on impacts on other populations and biodiversity/food-web stability.

A top predator can prevent one prey species from becoming too abundant, protecting plant communities and keeping habitats diverse.

They can change water flow, soil moisture, light levels or sedimentation, which reshapes the habitat.

Keystone species increase resilience by keeping key ecosystem functions and food-web relationships stable after disturbance.

Keystone species maintain stability, supporting faster recovery after disturbance.

Protecting a keystone species can protect many other species and maintain ecosystem services by keeping the system stable.

Look for “creates habitat”, “builds”, “digs”, “modifies environment”, or “changes water flow/soil structure”.