Ecosystems: Terminology and Levels of Organization

Module Progress:

Ecosystems are incredibly diverse, wide-ranging and ever changing. It is important then, to have agreed upon terms so that comparisons can be made. In this module, you’ll get an overview of the important terms used in ecology to describe different aspects of an ecosystem. This list of terms also serves to illustrate how the different levels of an ecosystem are organized, starting from individual organisms up to whole systems.


A single individual of a species. These individuals respond to the factors of the environment, and the organism’s particular degree of tolerance to stresses in the environment determine where it will live.


Any organisms with similar features, role in an ecosystem, who evolved from a common ancestor, and can reproduce in nature to form fertile offspring, are considered to be a part of the same species, this definition is well accepted by the scientific community, however, a ‘species’ is difficult to define, as it is a human-imposed concept that doesn’t necessarily occur in nature. To learn more about the challenges of defining ‘species’, please see the following:

DEFINING A SPECIES- Understanding Evolution

Engage: Think back to the first farm-based activity in Lesson 1. What are some of the species you observed on or around your farm? Were there any you hadn’t realized were part of that ecosystem?

Single-Celled Bacterial Microorganism Single Plant Organism Single Animal Organism
E. Coli Soil Bacteria Delonix regia seedling Single Vicugna pacos
46806003 96544460


A group of organisms of the same species who live in the same place. Population ecology can allow us to understand the factors that control population size and growth, especially in relation to the capacity of the environment to support a particular population over time. Did you observe a population in your ecosystem? For example, a grove of trees (if they were the same species) would be a population.

Population of Earthworms Population of Soybeans Population of Caribou
Population of Eisenia fetida Population of Glycine max Population of Rangifer tarandus
 16775732  42794676(1)  22012036


A group of populations of various species living together and interacting with one another. The interactions of organisms and populations of different species affect the distribution and abundance of different species that make up a particular community. In a community, organisms of different species are both dependent upon and in competition with other organisms in an ecosystem.

Species diversity:

The number of species that occur in a community. Some communities are extremely diverse, with many different species, while others are composed of relatively few species. There are some technical terms to quantify the diversity in a determined place, for example, species richness measures the number of different species in certain place, and species evenness refers to how close in numbers each species in a place is. There are multiple diversity indexes that combine species richness and evenness that are used to express how diverse is a place.

Soil Microbial Community Community Community
Soil microbial community of yeast, bacteria & fungi Savannah community Silvo-pastoral community of grasses, shrubs, trees and cows
28691634 10484836(1)  63499809


The ecosystem is the interactions of all the communities of organisms along with the abiotic factors of the environment within a particular area. The boundaries of an ecosystem are arbitrary. There is an intricate web of interaction and functions that occur within the structure of the ecosystem.

Ecosystem ecology:

The study of living (biotic) and non-living (abiotic) components of ecosystems and their interactions within an ecosystem. This science examines how ecosystems work and relates this to their components such as chemicals, bedrock, soil, plants, and animals.

Ecosystem Ecosystem Ecosystem
Desert ecosystem Pond ecosystem Agricultural ecosystem
 53568889  27843871  28579613


An ecosystem that has been altered or manipulated for the purpose of establishing agricultural production. The processes, structures and characteristics of natural ecosystems can be observed in agroecosystems. Using the agroecosystem framework, we can analyze food production systems as wholes, including the complex inputs and outputs and interconnections of their component parts. Agroecosystems are infinitely complicated because they include humans and social structures. By extending the agroecosystem concept further, we can incorporate social systems, as the structures within which humans as food consumers organize food distribution through markets and other means.

Agroforestry System Chinampas Agroecosystem Push-Pull Agroecosystem
 32313980  63363412  10605120

Emergent properties

Another characteristic of ecosystems is that at each level of organization, properties emerge that were not present at the level below. These emergent properties are the result of the interaction between the structure and function of the “parts” of that level of ecosystem organization. For example, in a population, there is more than just a collection of individuals of the same species, which has characteristics that cannot be understood in terms of individual organisms alone. As you might have experienced, an agroecosystem is so much more than just the sum of its individual crop plants.