Ecology is the scientific study of how organisms interact with each other and their surroundings. While “community” and “ecosystem” are often used interchangeably in everyday conversation, scientifically they represent two distinct levels of biological organization. Understanding the specific components and interactions that define each concept is fundamental to accurately studying life on Earth, allowing researchers to focus on different scales of interaction.
What Defines a Biological Community
A biological community is defined by the collection of all living populations—plants, animals, fungi, and microorganisms—that inhabit a specific geographic area. The focus is exclusively on the interactions that occur between these different species populations.
The relationships within a community are varied, driven by the need to secure resources. These interspecies relationships include negative interactions like predation and competition for limited resources. Positive interactions are also common, such as mutualism, where both species benefit, or parasitism, where one species benefits at the expense of the other. The study of a community analyzes this complex network of living interactions.
What Defines an Ecosystem
The concept of an ecosystem expands upon the biological community by incorporating the physical environment. An ecosystem consists of the biological community plus all the non-living (abiotic) chemical and physical factors that influence the organisms within that area. This addition of the non-living component distinguishes an ecosystem from a community.
Abiotic factors, such as water availability, soil composition, temperature, and sunlight intensity, determine what types of species can thrive in a location. An ecosystem functions as a complete, self-sustaining unit because it includes mechanisms for energy flow and nutrient cycling. Energy enters the system primarily through sunlight captured by producers, and elements cycle between the living organisms and the atmosphere, soil, and water. This constant exchange of energy and matter is the defining process of an ecosystem.
The Essential Difference
The fundamental difference between a community and an ecosystem rests on the inclusion of the non-living environment. A community is a purely biological concept, encompassing only living organisms and their relationships with one another. Researchers studying a community focus on species interaction, such as how two plant species compete for space.
An ecosystem includes the community as one of its components, adding the physical environment. The study of an ecosystem analyzes how living organisms interact with both each other and with the non-living elements, such as how soil moisture affects plant growth and the animals that eat those plants.
Placing Them in Ecological Context
The community and the ecosystem fit sequentially into the broader organizational structure ecologists use to study nature. This hierarchy begins with individual organisms, which form populations of the same species, and those populations then combine to form the community. The community is the highest level of organization composed entirely of living things.
The ecosystem sits directly above the community in this hierarchy, representing the first level that integrates the physical environment. Since the ecosystem is defined as the community plus its non-living surroundings, the community is always a component of the larger ecosystem. This structural relationship illustrates that the function of the living community is linked to the physical conditions of the surrounding ecosystem.