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.

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.

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.

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)

Organism

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

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.

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.

Community

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

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.

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.

Biosphere

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

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).

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.

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.

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?