Ecologists study life at different sizes, the way a map can show one street or a whole state. Each level adds something to the one below it. You already know the biotic and abiotic parts from Living and Nonliving Parts.
Key idea
Organism: one living thing. Population: all the members of one species in an area. Community: all the populations of different species living there. Ecosystem: the community plus the abiotic parts.
| Level | In a pond | What it adds |
|---|---|---|
| Organism | one bluegill fish | a single living thing |
| Population | all the bluegills in the pond | many of one species |
| Community | bluegills, frogs, algae, cattails, snails … | every species together |
| Ecosystem | the community plus water, mud, sunlight | the nonliving parts |
| Biome | all freshwater lakes and ponds with similar conditions | a large region (next topics) |
Why it works
A population matters because its members can breed with each other and compete for exactly the same food and space. That is why the word is kept for one species. Different species in the same place interact in other ways, as predators, prey and partners, so together they get a different name: the community.
Worked example: Population or community?
A student writes: "The animals in the pond are a population." Is that right?
- How many species are named? The animals of a pond include frogs, fish, snails and insects: several species.
- A population has only one species.
- Several species living together form a community (and plants and microbes belong to the community too).
Answer: No. The animals of a pond are part of a community. "All the green frogs in the pond" would be a population.
Common mistake
Students call all the animals in a pond a population. A population is always one species. Check by asking: could I name these with one species name? If you need several names, it is a community.