Ecology is the study of how organisms interact with each other and with their environment.
ORGANISM — an individual living thing (e.g. one robin, one oak tree, one earthworm).
POPULATION — all the individuals of ONE SPECIES living in the same area at the same time (e.g. all the robins in a woodland).
COMMUNITY — all the populations of DIFFERENT SPECIES living together in the same area (e.g. all the animals, plants, fungi and microorganisms in a woodland).
HABITAT — the specific place where an organism lives within an ecosystem (e.g. the woodland floor, the canopy, a particular pond).
ECOSYSTEM — a community of organisms PLUS all the non-living (abiotic) factors in the same area. An ecosystem includes everything — living and non-living — in a defined area.
Interdependence in Ecosystems
All species within a community are INTERDEPENDENT — they depend on each other directly or indirectly for their survival.
If one species changes significantly, it affects others — sometimes the effects ripple through the whole ecosystem (called a CASCADE EFFECT).
Examples of interdependence:
Plants depend on bees for POLLINATION — without bees, many plants cannot reproduce.
Bees depend on flowering plants for NECTAR and POLLEN — their food source.
Shrews depend on earthworms for food.
Earthworms depend on leaf litter (decomposing plant material) for food.
Deer depend on grass and shrubs for food.
Wolves depend on deer as prey.
If wolves are removed → deer population explodes → vegetation is overgrazed → many plant species decline → animals that depend on those plants also decline.
A STABLE COMMUNITY is one where populations remain roughly constant over time — because the various checks and balances (predation, competition, disease) keep each population within its range.
Types of Ecosystem
Ecosystems exist at many scales and in many environments.
BIOTIC FACTORS (which species live there, what eats what).
LEVEL OF PRODUCTIVITY (how much energy is fixed by plants).
⚠️ Common Mistake
Students often confuse COMMUNITY and ECOSYSTEM. A community is all the LIVING ORGANISMS in an area. An ecosystem includes the community PLUS all the non-living (abiotic) factors. Remember: Ecosystem = Community + Abiotic environment.
📌 Key Note
Organism → Population (one species) → Community (all species) → Ecosystem (community + abiotic factors). All species are interdependent — changes to one affect others (cascade effect). Stable community = populations roughly constant over time.
🎯 Matching Activity — Match the Ecology Term
Match each term to its correct definition. — drag the symbols on the right to match the component names on the left.
Population
Drop here
Community
Drop here
Ecosystem
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Habitat
Drop here
Interdependence
Drop here
ALL populations of different species living together in the same area
All species in a community depend on each other directly or indirectly
All individuals of ONE species in a given area
The specific place where an organism lives
Community PLUS all the non-living (abiotic) factors in the same area
⭐ Higher Tier Only
Students should be able to explain how changes to abiotic and biotic factors affect communities, using data as evidence. Stable communities have balanced interactions — changes to one component ripple through the whole system. The concept of the ecosystem as a self-sustaining unit with inputs (sunlight, inorganic nutrients) and outputs (heat, waste) is important for understanding sustainability.
🎯 Test Yourself
Question 1 of 3
1. What is the difference between a community and an ecosystem?
2. Wolves are removed from a woodland ecosystem. What is the most likely consequence?
3. Why do artificial ecosystems (like farmland) tend to have lower biodiversity than natural ecosystems?
⭐ How Well Do You Understand This Topic?
Be honest with yourself — this helps you know what to revise!
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