Level Classifications in Ecology: Overview

All of the organisms on Earth form relationships with each other, other organisms, their environment, and non-living (aka abiotic) factors in the world. The study of these relationships and interactions is generally known as ecology.

However, there are various levels of classification and areas of focus within ecology as a whole. They're often described as going from a broad area of study to a more narrow area of study. These different classes of ecological study are also used to describe how organisms and environments are organized in the world overall.


A biome is defined as a large geographical area that's defined by the plants, animals, and other organisms that inhabit it. This is the largest and most broad ecological classification.

The following are the types of biomes found on Earth:

  • Rainforest (either tropical or temperate)
  • Temperate forest
  • Taiga
  • Tropical grassland
  • Temperate grassland
  • Desert
  • Tundra
  • Aquatic (either freshwater or marine)

Within biomes you'll find various different ecosystems, environments, habitats, communities, and populations. The types of flora and fauna you'll find here are often determined by the climate of the geographical area.

Ecologists can specialize in studying ecological relationships within specific biomes.


The next level that's slightly less broad than a biome is an ecosystem. An ecosystem is defined as all of the biotic (living) and abiotic (non-living) factors in a specific area.

This includes all of the organisms, microorganisms, rocks, soil, air, weather, etc, and all of the relationships between these things.

Ecosystems are slightly more specific classifications compared to biomes. For example, under the classification of marine biome, you could have any of the following ecosystems:

  • Beaches
  • Estuaries
  • Open ocean
  • Coral reefs
  • Oceanic trenches

Abiotic and biotic factors depend on each other and interact constantly within ecosystems. It's within ecosystems that you can observe the food chain, energy flow, biogeochemical cycles, and other similar concepts.

Community Ecology

A community is defined as a group of various populations of organisms interacting within a certain area. An example would be all of the trees, birds, squirrels, soil microorganisms, and insects in a forest.

Community ecology is the study of how these organisms interact. Take note that each subsequent level gone over here gets increasingly specialized and specific.

Community ecology falls under the general study of ecology with the focus on the organization, function, and interaction within biological communities.

Population Ecology

Each community is made up of various populations of organisms that interact with each other. Thus, population ecology is the study of individual populations of organisms.

The definition of a population in biology is a group of organisms of the same species living within the same general area. This could be all of the clown fish in a coral reef, red tail hawks in a deciduous forest, mountain goats in a mountain range, etc.

Population ecologists study population size, population growth, changes in population over time, dispersion of populations, and population density.

Organism Ecology

Each population is made up of individual organisms of a particular species. An organism is defined as an individual living thing. This can range from a bacterium to an elephant to a sunflower.

Most ecologists who study organisms focus on a particular species or class of organism. The definition of organismal ecology is the study how organisms behave, what they eat, how they function, and studies of their physiology in response to environmental conditions.

Each organism or population of organisms fills an ecological niche within their habitat, community, or ecosystem. Scientists also study these niches and how they influence evolution, adaptation, and more.

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