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18.1: Biological Communities

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  • Where can you find an ecosystem?

    Just about everywhere you could go in nature, you would be taking a field trip to an ecosystem. There are underwater ecosystems and coastal ecosystems. There are small scale ecosystems and large ones. There are even ecosystems inside your body!

    What Is An Ecosystem?

    An ecosystem is a group of living things and their environment. The word ecosystem is short for “ecological system.” Like any system, an ecosystem is a group of parts that work together. You can see examples of ecosystems in Figure below. The forest pictured is a big ecosystem. Besides trees, what living things do you think are part of the forest ecosystem? The dead tree stump in the same forest is a small ecosystem. It includes plants, mosses, and fungi. It also includes insects and worms.

    A forest and tree stump are both ecosystems

    An ecosystem can be big or small. A small ecosystem can be part of a larger ecosystem.

    Abiotic Factors

    Abiotic factors are the nonliving parts of ecosystems. They include air, sunlight, soil, water, and minerals. These are all things that are needed for life. They determine which living things—and how many of them—an ecosystem can support. Pictured below is an ecosystem and its abiotic factors (Figure below).

    Diagram of abiotic factors of an ecosystem

    Which abiotic factors do you see here?

    Biotic Factors

    Biotic factors are the living parts of ecosystems. They are the species of living things that reside together.

    Species, Niche, and Habitat

    A species is a unique type of organism. Members of a species can interbreed and produce offspring that can breed (they are fertile). Organisms that are not in the same species cannot do this. Examples of species include humans, lions, and redwood trees. Can you name other examples?

    Each species has a particular way of making a living. This is called its niche. You can see the niche of a lion below (Figure below). A lion makes its living by hunting and eating other animals. Each species also has a certain place where it is best suited to live. This is called its habitat. The lion’s habitat is a grassland. Why is a lion better off in a grassland than in a forest?

    Lion hunting a zebra

    A lion hunts a zebra. What is the lion's niche?

    Living Together

    All the members of a species that live in the same area form a population. Many different species live together in an ecosystem. All their populations make up a community. What populations live together in the grassland pictured above (Figure above)?


    • All of the individuals of a species that exist together at a given place and time make up a population. A community is made up of all of the populations in an area.
    • The living and nonliving factors that living organisms need plus the communities of organisms themselves make up an ecosystem.
    • A habitat is where an organism lives, and a niche is what it does to make a living.


    1. Define species, population, community, niche, habitat, biotic factor, and abiotic factor.
    2. Compare a lion and a deer. Which biotic and abiotic factors that each of these animals needs to live are the same?
    3. Which biotic and abiotic factors are different between a lion and a deer?

    Explore More

    Use the resource below to answer the questions that follow.

    1. What are the biotic components of an ecosystem?
    2. What is a species?
    3. What is a population?
    4. List two examples of populations.
    5. What is a community?
    6. What is different between the size of an ecosystem and the size of a natural community?
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