Ecological Levels of Organization

Picture the Earth. The Earth is a gigantic place, isn’t it? Now imagine zooming in. You might picture mountain ranges and oceans. Zoom in further, and you might think of whole forests or coral reefs teeming with life. And when you try to zoom in even closer, you might imagine squirrels climbing trees or fishes swimming among the coral reefs. 

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Table of contents

    When we study Ecology, we can look at interactions from the global level down to the single organism. We call these the Ecological Levels of organization. So, it's time to get started!

    • First, we will look at the definition of Ecological Levels of organization.
    • Then, we will look at the pyramid showing these different ecological levels of organization.
    • After, we will explore each of these levels of ecological organization.
    • Then, we will look at some examples involving these levels of organization and at an activity.
    • Lastly, we will talk about the application of these ecological levels of organization in research.

    Ecological Levels of Organization Definition

    Ecology looks into how organisms interact with each other and their environment. Because studying all living things and their interactions can be overwhelming, we look at ecology at different levels.

    The term “ecological levels of organization” refers to how the biological world at and above the level of the individual organism is organized into a nested hierarchy, providing specific frames of reference to study ecology.

    Ecological levels of organization pyramid

    The ecological levels of organization can be visualized as a pyramid as shown in figure 1:

    At each level, ecologists are interested in studying different processes.

    • At the organism/individual level, ecologists focus on an organism's survival and Reproduction.
    • At the population level, ecologists study Population Dynamics.
    • At the community level, ecologists are interested in the interactions among species.
    • At the ecosystem level, ecologists are interested in studying the flow of matter and energy.
    • At the biosphere level, ecologists look at global processes.

    Did you know that organisms are considered the unit of Natural Selection? You can learn more about this by looking at "Natural Selection"!

    Levels of Ecological Organization from Smallest to Largest

    The levels of ecological organization from smallest to largest are as follows: organism, population, community, ecosystem, and biosphere.

    (smallest) organism ⇾ population community ecosystem biosphere (largest)

    Let's discuss each one in more detail.

    Organism

    Organisms (also called individuals) are the most fundamental unit of ecology.

    An organism is a living entity with key characteristics such as order, Response to Stimuli, growth and development, Reproduction, regulation, and energy processing.

    Organisms can be prokaryotic or eukaryotic:

    • Prokaryotes are simple, single-celled organisms whose Cells lack membrane-bound organelles. Archaea and Bacteria fall under this category.

    • Eukaryotes are more complex organisms whose Cells have membrane-bound organelles, including the nucleus. Plants, Animals, Fungi, and protists fall under this category.

    Population

    Next, we have population.

    A population is a group of organisms that are part of the same species living in the same area and potentially interacting with each other.

    Populations can be identified based on where they live, and their areas may have natural (rivers, mountains, deserts) or artificial (man-made structures such as roads) boundaries.

    • The geographic range of a population (or distribution) refers to the area of land or water that it resides within.

    Looking for more information on population behavior? "Group Behavior Biology" is a must-read!

    Community

    After organism and population, we come across the community level of ecological organization.

    A community is a group of Populations of different species that live in the same area and potentially interact with one another. A community can be made up of Animals, Plants, Fungi, Bacteria, etc.

    Communities may cover large areas like forests, or they may cover very small areas like Microorganisms living in the digestive system of an animal.

    Community interactions fall into three broad categories:

    • Competition is when different organisms or species compete for limited resources, including food, territory, and water.

    • Predation is when a species (called predator) consumes another species (called prey).

    • Symbiosis is when the interaction between two species benefits one or both species. There are three types of symbiosis:

      • Commensalism is when an interaction benefits one species but does not affect the other.

      • Mutualism is when an interaction benefits both species.

      • Parasitism is when an interaction benefits one species but harms the other.

    Ecosystem

    At the next level of ecological organization, we have the ecosystem.

    An ecosystem is the combination of all Biotic and Abiotic Factors in a given area.

    Whereas biotic factors are living organisms such as plants, animals, and bacteria, abiotic factors are nonliving things such as soil, water, temperature, and wind.

    In simpler terms, an ecosystem involves one or more Communities of living organisms in interaction with their non-living physical and chemical environment.

    An ecosystem can exist in different sizes: a stream, a meadow, and a hardwood forest are all examples of Ecosystems!

    Biosphere

    Lastly, we have the biosphere. The biosphere is at the highest level of ecological organization.

    The biosphere is composed of all the Ecosystems on Earth. It is also referred to as the zone of life on Earth because it is made up of parts of Earth where life exists.

    The biosphere includes:

    • The lithosphere (the outer region of the Earth).

    • The troposphere (the lower region of the atmosphere).

    • The hydrosphere (the collection of all of Earth’s water resources).

    It was thought that the biosphere range extended from a few kilometers into the atmosphere up to the deep-sea vents of the ocean; however, it is now known that some microbes can survive even several kilometers into the Earth’s crust.

    The exchange of energy and nutrients between distant ecosystems is facilitated by wind currents, water, and organism movement (for example, during migration).

    Some references consider another ecological level of organization: the biome. It falls between the ecosystem and the biosphere.

    A biome is a major life zone characterized by the type of vegetation (in terrestrial biomes) or the general physical environment (in aquatic biomes) it has. A biome may contain multiple ecosystems.

    Terrestrial biomes include deserts, savannas, tundras, and tropical forests, whereas aquatic biomes include lakes, wetlands, estuaries, intertidal zones, and coral reefs.

    Rather than distinct boundaries, biomes have transition zones called ecotones which have species from both biomes.

    Ecological Levels of Organization Examples

    Let’s look at specific examples (table 1) of each ecological level of organization to help you understand these concepts better.

    Table 1. Examples of each ecological level of organization.

    Ecological level

    Example

    Organism

    An individual white-tailed deer

    Population

    A herd of white-tailed deer

    Community

    Forest community consisting of white-tailed deer, oak trees, apple trees, tapeworms, gray wolves, coyotes, and bears

    Ecosystem

    The Wisconsin hardwood forest ecosystem (including its soil, water, temperature, and air)consisting of

    Biome

    Temperate forest

    Ecological Levels of Organization Activity

    Let’s try an activity to help you practice what you have learned so far. First, look at the two images below. Then, try to identify in these images examples of each ecological level and fill in Table 2 below as we did in Table 1.

    Table 2. Ecological levels of organization activity.

    A

    B

    Organism

    Population

    Community

    Ecosystem

    Biome

    Ecological Levels of Organization Application in Research

    Now that we know the definition of each ecological level of organization, let’s move on to how these levels are applied.

    Remember earlier when we defined ecological levels of organization as specific frames of reference in studying ecology? Here, we’ll look into examples of what scientists might want to study at each ecological level:

    • Scientists studying organismal ecology are interested in the biological adaptations that enable an organism to survive in its habitat. Such adaptations can be morphological, physiological, or behavioral.

      • Example of a research question: What is the typical behavior of white-tailed deer at its different life stages?

    • Scientists studying population ecology are often interested in understanding how and why a population changes in size over time.

      • Example of a research question: How do man-made structures affect the distribution of white-tailed deer in the Wisconsin forest?

    • Scientists studying Community Ecology are interested in processes that drive interactions between and among different species and the consequences of such interactions.

      • Example of a research question: How does the density of white-tailed deer affect the diversity and abundance of the herbaceous components of forest understories?

    • Scientists studying ecosystem ecology are interested in how nutrients, resources, and energy are transferred between living and nonliving components of an ecosystem.

      • Example of a research question: What are the impacts of natural and man-made disturbances on the Wisconsin hardwood forest ecosystem?

    • Scientists studying the biosphere take on a global perspective and are interested in topics such as climate change and global air circulation patterns.

      • Example of a research question: How does deforestation contribute to climate change?

    Did you know that there is a whole community of Microorganisms in your gut? How about on the surface of your skin?

    Communities of microorganisms (called microbiomes) can be found on or in people, animals, and the environment. These microbiomes can help us maintain good health and even fight infections. However, microbiomes can become unbalanced, for example, when someone has an Infectious Disease or takes antibiotic medication.

    A lot of research goes into studying these microbial communities and their interactions with their environment–a discipline that is called microbial ecology–because these play a big role in human health.

    Untitled note - Key takeaways

    • Ecological levels of organization refers to how the biological world is organized into a nested hierarchy, providing specific frames of reference to study ecology. The levels of ecological organization from smallest to largest are as follows: organism, population, community, ecosystem, biome, and biosphere.
    • An organism is a living entity with key characteristics such as order, Response to Stimuli, growth and development, reproduction, regulation, and energy processing.
    • A population is a group of organisms that are part of the same species living in the same area and potentially interacting with each other.
    • A community is a group of populations of different species that live in the same area and potentially interact with one another. A community can be made up of animals, plants, fungi, bacteria, etc.
    • An ecosystem is the combination of all Biotic and Abiotic Factors in a given area.
    • The biosphere is composed of all the ecosystems on Earth.

    References

    1. Suzanne Wakim & Mandeep Grewal, Introduction to Ecology via Biology LibreTexts, 27 Dec 2021.
    2. Andrea Bierema, Introduction to Ecology - An Interactive Introduction to Organismal and Molecular Biology, accessed 1 Dec 2021.
    3. David Gates, "Biosphere", Encyclopedia Britannica, 6 Oct 2022.
    4. Jake Parr, The White Tailed Deer, 27 Apr 2007.
    5. Biology LibreTexts, The Biosphere, 4 Jan 2021.
    6. Centers for Disease Control and Prevention, About Microbial Ecology, 22 July 2022.
    Frequently Asked Questions about Ecological Levels of Organization

    What are the 5 ecological levels of organization?

    The 5 ecological levels of organization (from smallest to largest) are as follows: organism, population, community, ecosystem, and biosphere.

    Why is ecological levels of organization important?

    The ecological levels of organization is important because studying all living things and their interactions can be overwhelming.

    What are the levels of ecological organization in order?

    The levels of ecological organization in order (from smallest to largest) are as follows: organism, population, community, ecosystem, and biosphere.

    What is the most basic level of ecological organization?

    The most basic level of ecological organization is the organism.

    What is the most important level of organization of ecology? 

    There is no most important level of organization in ecology. It just depends on the ecologist and what they are interested in. For example, Scientists studying organismal ecology are interested in the biological adaptations that enable an organism to survive in its habitat. For them, the most important level is the organism/individual level. 

    Test your knowledge with multiple choice flashcards

    A/n _____ is a group of organisms that are part of the same species living in the same area and potentially interacting with each other.

    A/n ______ is a group of populations of different species that live in the same area and potentially interact with one another. 

    _____ is when an interaction benefits one species but does not affect the other.

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