Communities & ecosystems
Big idea: Living things are never alone! They form communities and, together with their surroundings, create ecosystems.
What is a community?
A community is like all the students, teachers, and staff in your school — everyone living and working together, but only the living things count!
- Made up of many populations (like different classes or clubs)
- Includes producers (plants), consumers (animals), and decomposers (fungi, bacteria)
- All live in the same place at the same time
- Species interact: some help each other, some compete, some eat others
Community = living things only. No rocks, water, or sunlight included!
What is an ecosystem?
An ecosystem is like your school plus everything in it — people, buildings, playground, air, and even the weather!
- Includes a community (all living things)
- Also includes non-living things: sunlight, water, temperature, soil, rocks
- Energy flows through (like food chains and webs)
- Matter is recycled (like composting or water cycles)
Ecosystem = community + non-living environment. Both are needed!
Community vs ecosystem (exam favourite)
Community
- Only living things (plants, animals, fungi, bacteria)
- Made of different populations
- Focuses on how species interact (like food chains, competition, cooperation)
Ecosystem
- Living + non-living things (add water, sunlight, soil, etc.)
- Includes abiotic (non-living) factors
- Focuses on energy flow (who eats whom) and matter cycling (nutrients, water)
Exam tip: If a question mentions abiotic factors (like temperature, water, or sunlight), it’s about an ecosystem, not just a community!
Habitats
A habitat is like your home — it’s the special place where a species lives and finds what it needs to survive.
- One habitat can be home to many different species (like a park with birds, insects, and trees)
- Different habitats support different communities (desert vs. rainforest)
- The type of habitat decides which species can survive there (fish need water, cacti need dry land)
Open ecosystems
Most ecosystems are open systems — like a classroom with open doors and windows.
- Energy comes in as sunlight (like light entering a room)
- Matter (water, nutrients, animals) moves in and out (like students and supplies entering and leaving)
- Ecosystems are connected to their surroundings (like classrooms in a school)
Ecosystems are dynamic — always changing because things can enter and leave.
Scale of ecosystems
Ecosystems come in all sizes — from tiny ponds to the whole planet! The scale you choose changes what you see.
- Small scale: a puddle, a garden, a single tree
- Medium scale: a forest, a lake, a coral reef
- Large scale: a whole biome (like the Sahara Desert), or even the entire Earth
Zooming in or out (changing scale) helps you focus on different interactions — like looking at a leaf vs. the whole forest.