Main content
Biology library
What is an ecosystem?
Learn what an ecosystem is, how energy and matter move through ecosystems, and what makes an ecosystem stable.
Key points
- An ecosystem consists of a community of organisms together with their physical environment.
- Ecosystems can be of different sizes and can be marine, aquatic, or terrestrial. Broad categories of terrestrial ecosystems are called biomes.
- In ecosystems, both matter and energy are conserved. Energy flows through the system—usually from light to heat—while matter is recycled.
- Ecosystems with higher biodiversity tend to be more stable with greater resistance and resilience in the face of disturbances, or disruptive events.
Introduction
What do a tide pool on the California coast and the Amazon rainforest of South America have in common? Despite being many orders of magnitude different in size, both are examples of ecosystems—communities of organisms living together in combination with their physical environment.
As a reminder, a community consists of all the populations of all the species that live together in a particular area. The concepts of ecosystem and community are closely related—the difference is that an ecosystem includes the physical environment, while a community does not. In other words, a community is the biotic, or living, component of an ecosystem. In addition to this biotic component, the ecosystem also includes an abiotic component—the physical environment.
Ecosystems can be small, such as the tide pools found near the rocky shores of many oceans, or very large, such as the Amazon Rainforest in South America. It's basically up to the ecologist studying the ecosystem to define its boundaries in a way that makes sense for their questions of interest.
What are ecosystems like?
The short answer: incredibly diverse! Not only can ecosystems vary in size, but they can also differ in just about every imaginable biotic or abiotic feature.
Some ecosystems are marine, others freshwater, and others yet terrestrial—land based. Ocean ecosystems are most common on Earth, as oceans and the living organisms they contain cover 75% of the Earth's surface. Freshwater ecosystems are the rarest, covering only 1.8% of the Earth's surface. Terrestrial, land, ecosystems cover the remainder of Earth.
Terrestrial ecosystems can be further grouped into broad categories called biomes, based largely on climate. Examples of terrestrial biomes include tropical rain forests, savannas, deserts, coniferous forests, deciduous forests, and tundra. The map below shows the broad distribution of biomes on Earth.
Even within a biome, there can be great diversity. For example, both the Sonoran desert, on the left, and the interior of the island of Boa Vista, on the right, can be classified as deserts, but they have very different ecological communities. Many more species of plants and animals live in the Sonoran desert.
Energy and matter in ecosystems
Ecosystem ecologists are often most interested in tracing the movement of energy and matter through ecosystems.
We’ll take a closer look at the movement of energy and matter when we consider food webs, networks of organisms that feed on one another, and biogeochemical cycles, the pathways taken by chemical elements as they move through the biosphere. The organisms found in an ecosystem tend to have adaptations, beneficial features arising by natural selection, that help them get energy and matter in the context of that particular ecosystem.
Before we get into details, though, let’s look at the key features of how energy and matter travel through ecosystems. Both energy and matter are conserved, neither created nor destroyed, but take different routes through ecosystems:
- Matter is recycled; the same atoms are reused over and over.
- Energy flows through the ecosystem, usually entering as light and exiting as heat.
Matter is recycled.
Matter is recycled through Earth’s ecosystems—though it may move from one ecosystem to another as it does when nutrients are washed away into a riverstart superscript, 1, end superscript. The same atoms are used over and over again, assembled into different chemical forms and incorporated into the bodies of different organisms.
As an example, let’s see how chemical nutrients move through a terrestrial ecosystem. A land plant takes in carbon dioxide from the atmosphere and other nutrients, such as nitrogen and phosphorous, from the soil to build the molecules that make up its cells. When an animal eats the plant, it uses the plant’s molecules for energy and as building material for its own cells, often rearranging atoms and molecules into new forms.
When plants and animals carry out cellular respiration—break down molecules as fuel—carbon dioxide is released into the atmosphere. Similarly, when they excrete waste or die, their chemical compounds are used for energy and building material by bacteria and fungi. These decomposers release simple molecules back into the soil and atmosphere, where they can be taken up anew in the next round of the cycle.
Thanks to this recycling, the atoms that make up your body right now have long, unique histories. They’ve most likely been part of plants, animals, other people, and even dinosaurscubed!
Energy flow is unidirectional, or one-way.
Energy, unlike matter, cannot be recycled in ecosystems. Instead, energy flow through an ecosystem is a one-way street—generally, from light to heat.
Energy usually enters ecosystems as sunlight and is captured in chemical form by photosynthesizers like plants and algae. The energy is then passed through the ecosystem, changing forms as organisms metabolize, produce waste, eat one another, and eventually, die and decompose.
Each time energy changes forms, some of it is converted to heat. Heat still counts as energy—and thus no energy has been destroyed—but it generally can't be used as an energy source by living organisms. Ultimately, energy that entered the ecosystem as sunlight is dissipated as heat and radiated back into space.
This one-way flow of energy through ecosystems means that every ecosystem needs a constant supply of energy, usually from the sun, in order to function. Energy can be passed between organisms, but it cannot be recycled because some of it is lost as heat in each transfer.
Stability and dynamics of ecosystems
Ecosystems are dynamic systems, and a static ecosystem would be a dead ecosystem—just as a static cell would be a dead cell. As we discussed above, energy is constantly flowing through an ecosystem and chemical nutrients are continually being recycled. At higher levels of organization, organisms are dying and being born, populations are fluctuating in their numbers, and climate patterns are varying seasonally and in less predictable ways.
Equilibrium and disturbance
Equilibrium is the steady state of an ecosystem, in which its composition and identity remain generally constant despite fluctuations in physical conditions and the makeup of the biotic community. Ecosystems may be knocked out of equilibrium by disturbances, disruptive events that affect their composition.
Some disturbances are a result of natural processes. For example, fire is a disturbance that can be caused by lightning in a prairie or forest ecosystem. Other disturbances are the result of human activities. Examples include acid rainfall, deforestation, algal blooms, and the introduction of invasive species.
Different ecosystems may respond differently to the same disturbance; one may recover rapidly, and another may recover more slowly—or not at all.
Resistance and resilience
Ecologists sometimes use two parameters to describe how an ecosystem responds to disturbance. These parameters are resistance and resilience. The ability of an ecosystem to remain at equilibrium in spite of disturbances is called resistance. How readily an ecosystem returns to equilibrium after being disturbed is called resilience. Some ecologists consider resistance to be an element of resilience—one that acts on a short timescalestart superscript, 4, comma, 5, end superscript.
Many ecologists think that the biodiversity of an ecosystem plays a key role in stability. For example, if there were just one plant species with a particular role in an ecosystem, a disturbance that harms that one species—say, a drought for a drought-sensitive species—might have a severe impact on the ecosystem as a whole. In contrast, if there were several plant species with similar functional roles, there would be a better chance of one of them being drought-tolerant and helping the ecosystem as a whole survive the drought periodstart superscript, 6, end superscript.
Ecosystem resistance and resilience are important when we consider the effects of disturbances caused by human activity. If a disturbance is severe enough, it may change an ecosystem beyond the point of recovery—push the ecosystem into a zone where it is no longer resilient. A disturbance of this sort could lead to permanent alteration or loss of the ecosystem.
Want to join the conversation?
Is biodiversity something that can be artificially encouraged? Like, if biodiversity is important for promoting resistance/resilience, how can an ecosystem increase their biodiversity? Is that something that only comes about after long periods of equilibrium (species are allowed to mutate, occupy specialized niches, etc)? Or can humans speed up the process, perhaps by introducing species from similar ecosystems and allow them to spread and take hold, thus increasing biodiversity in an ecosystem?(9 votes)
I do not think we can artificially boost it or promote successions biodiversity abundance etc.
All we can do is to try to interfere as less as possible and to eliminate human impact factor which destroys habitats.
People have been changing it for millennials! By introducing species, hunting for species and making them extinct, etc, but there is no way I think we can artificially boost and enhance it.
Even the idea of zoos is utterly dumb (in my opinion) and does no good. Safaris can let it slide.(6 votes)
why decidous forest are so called?(4 votes)- yes during fall the leaves start to fall off the trees, and thy grow back on untill summer.(5 votes)
why is this so long to read bruh like fr(5 votes)
Because this article is about ecosystems and many different things happen when you learn science.(10 votes)
- What makes up an eco-system?(6 votes)
- Biotic factors, such as producers and consumers, and abiotic factors, such as the temperature, soil, water and physiographic factors.(2 votes)
- what do biomes and ecosystem have in common(2 votes)
- Biome can be also called biotic community. It is the biotic environment of an ecosystem, as we know that ecosystem include living things (biotic factors) functioning together with the physical envionment (abiotic factors).(7 votes)
Why is it that all the ecosystems are so different? Can you find the same species in different ecosystems?(3 votes)- Yes, you can. But what makes an ecosystem is not just plenty of species but habitat and their interactions as well.(4 votes)
On the 2nd key point, it was mentioned that "Broad categories of terrestrial ecosystems are called biomes." I looked up "biome" on google and read that a biome is not an ecosystem.
So, are biomes ecosystems? Thanks.(3 votes)
No,It is not an ecosystem because it (biomes) is based on climate(2 votes)
Is climate change part of ecosystem.(3 votes)- Yes, it is.
Just like evolution is part of life and even the individual life of species. that way climate change is part of an ecosystem.(2 votes)
- How come all ecosystems are so diffrent? Can you like find the same organism in a diffrent ecosystem like in the other side of the world(3 votes)
why are biomes and climate so important for ecosystems?(2 votes)
Biomes are extremely important to continue life on Earth as it is known today, as each one helps to balance other biomes through climate and variation, and provides unique necessities to both biome and human. Climate is an important environmental influence on ecosystems. Changing climate affects ecosystems in a variety of ways. For instance, warming may force species to migrate to higher latitudes or higher elevations where temperatures are more conducive to their survival.(2 votes)
