Population in Ecosystems

Ecology studies the relationships between organisms and their environment, including abiotic (non-living) and biotic (living) factors. Here, we discuss how organisms interact with their own species define keywords in ecology, such as populations and niches.

Population in Ecosystems Population in Ecosystems

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Table of contents

    What is a population?

    We probably think about the human population when we hear the word population. However, we can also have populations of dogs, cats, wolves - basically any species. This is because a population is defined as all the individual organisms found in a given habitat of one species.

    Population: all the individual organisms found in a given habitat of one species.

    What is a community?

    A community is made up of all the various populations in a habitat. Species do not exist on their own; they interact with other species living in the same area to form communities.

    Community: all the living populations in a given area.

    A rainforest community might include several species of trees and shrubs growing at different heights and occupying different layers of the rainforest. It would also include the many birds, mammals, and insects who feed on these plants, as well as worms, fungi and bacteria that break down waste in the ecosystem.

    What is an ecosystem?

    So what is an ecosystem? An ecosystem includes the community of living organisms in a habitat and all the non-living (abiotic) components, such as water, soil and temperature. Ecosystems vary in size and scale. Some, such as ocean ecosystems, are extremely vast, while others, like pond ecosystems, are relatively small. Even humans can be considered ecosystems, as they are home to many complex interacting communities of microorganisms.

    Ecosystem: the collection of all communities in a habitat, together with the abiotic components.

    In a rainforest ecosystem, the plant community produces energy from the sun which is then consumed by the other organisms, and waste is recycled by other organisms in the system as well. In other words, the rainforest is a relatively self-sustaining unit. Little energy is exchanged between the rainforest and other ecosystems. However, no ecosystem is completely self-contained. For instance, many birds migrate between distant habitats at certain times of the year, thus linking multiple ecosystems.

    Ecosystems are dynamic and this is because the biotic and abiotic components are constantly in flux. Biotic factors, such as competition, and abiotic factors, such as temperature, can change at any time. These changes can happen at different rates, with some occurring very quickly (e.g., a decrease in population size due to the spread of a disease) and others very slowly (e.g. rocks undergoing erosion over time).

    Competition: where two organisms strive to obtain limited resource supplies. Intraspecific competition occurs between individuals of the same species whereas interspecific competition occurs between individuals of different species.

    Population in ecosystem Example of an ecosystem StudySmarterFig. 1 - Ecosystems

    Two major processes are very important to consider within an ecosystem. This includes the flow of energy and the flow of nutrients.

    Flow of energy

    First, there is a constant flow of energy between the organisms in the ecosystem, which occurs through feeding. Producers, such as plants, are eaten by primary consumers, who are then eaten by secondary consumers, who are eaten by tertiary consumers. When organisms die, they are decomposed and recycled.

    Producers: organisms that generate organic molecules, usually by photosynthesis.

    Consumers eat other organisms to obtain their energy, including primary, secondary and tertiary consumers.

    Flow of nutrients

    The second important process is the constant flow of nutrients within the ecosystem. Nutrients such as carbon, nitrogen, phosphorus, and important molecules such as water are recycled within the ecosystem.

    Carbon flows within the ecosystem in a process known as the carbon cycle. Carbon enters the atmosphere as carbon dioxide from the respiration of organisms, as well as emissions from factories, cities, and homes. It is then taken up by primary producers, who convert it into glucose during photosynthesis. Animals consume these plants and pass the energy along the food chain; they also continue to respire and release carbon as waste. Eventually, plants and animals die and decompose, and the carbon in their bodies returns to the atmosphere or is used as fuel.

    Population in Ecosystems carbon cycle StudySmarterFig. 2 - Carbon cycle

    What is a habitat?

    Organisms live in habitats, which are areas characterised by their physical conditions and occupants. An ecosystem is composed of several habitats.

    A rainforest ecosystem includes the canopy habitat, which might be home to some species of birds, as well as the forest floor habitat, which is home to fungi and small mammals. Habitats also house smaller units called microhabitats, which, as their name suggests, are home to organisms on an even smaller scale, such as worms and bacteria.

    What is a niche?

    In ecology, a niche describes the way that an organism fits into its environment. In other words, a niche is where the organism lives, what it does there, and how it interacts with others and its environment. It describes the organism’s role in the ecosystem.

    According to the competitive exclusion principle, no two species occupy the same niche in the same habitat. This is the proposition that two species that use the same limited resource cannot coexist at constant population levels, as even the slightest advantage of one species over another will allow the dominant species to outcompete the other to the point of extinction or exclusion. In other words, complete competitors cannot coexist.

    Population in Ecosystems - Key takeaways

    • A population is defined as all the organisms of a particular species in a given habitat. A community is defined as all of the populations that live together in a particular place at the same time.

    • A community is defined as all of the populations that live together in a particular place at the same time.

    • The two major processes to consider in an ecosystem are the constant flow of energy between organisms and the constant flow of nutrients in the ecosystem.

    • A niche describes the way that an organism fits into its environment. Due to the competitive exclusion principle, no two species can occupy the same niche.

    Frequently Asked Questions about Population in Ecosystems

    What is a population in an ecosystem?

    Members of the same species that live and interbreed with one another in the same habitat comprise a population. 


    Multiple populations of different species can exist and interact together as a community. An ecosystem is composed of one or more communities.

    How do populations change in an ecosystem?

    Ecosystems are dynamic. Many features within ecosystems, both biotic and abiotic, constantly undergo changes at many different rates. Populations are constantly changing, whether it’s in terms of their size or composition.

    How is competition responsible for population regulation in an ecosystem?

    Competition describes when organisms compete for the same resources within an environment. These resources, such as food, water, shelter, light and territory, are required for survival and reproduction. Members of the same species may also compete for mates. Competition among members of different species is referred to as intraspecific competition, while competition among members of the same species is called interspecific competition.

    What makes up an ecosystem?

    An ecosystem is comprised of the many communities in a habitat and the abiotic factors present. 

    What are some examples of populations in biology?

    Populations are composed of individual organisms in a given habitat of one species. 


    This can include a population of humans, a population of whales, or a population of donkeys!

    Test your knowledge with multiple choice flashcards

    A community is made up of many species. True or false?

    Ecosystems are dynamic - true or false?

    Which of the following traits is not likely to describe a pioneer species?

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