9.1 Ecosystems

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Main Content

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1. Key Definitions

Before diving into how ecosystems work, you need to know five important terms. Think of them like Russian nesting dolls — each one fits inside the next.

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Ecosystem

An ecosystem is a system made up of all the living things in an area together with the non-living environment around them, and all the interactions between them. A pond, a rainforest, a desert, or even a rotting log can each be an ecosystem. The key idea is that the living and non-living parts are connected and affect each other.

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Population

A population is all the individuals of the same species living in the same area at the same time. For example, all the rabbits living in one field make up a rabbit population. They can breed with each other and compete for the same resources.

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Community

A community is all the different populations of all species living together in the same area at the same time. If you take that field and count not just the rabbits but also the foxes, the grass, the oak trees, the beetles, and every other living thing — all of those together form the community.

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Habitat

A habitat is the place where an organism lives — the physical environment that provides everything it needs, such as food, shelter, and space. For example, a fish's habitat is a river or lake. A cactus's habitat is a desert.

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Niche

A niche is the role that an organism plays within its community — what it eats, what eats it, when it is active, and how it affects the environment. Think of the habitat as an organism's "address" and the niche as its "job." Two species cannot occupy exactly the same niche in the same place for long — one will always out-compete the other.