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5.1: Ecosystem Types and Dynamics

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    American beaver

    Figure \(\PageIndex{1}\): In semi-urban areas beavers (Castor canadensis) are considered a nuisance as their dams block drainage pipes and cause flooding. However, in wild areas beavers are one of the most important species. Beaver dams are known for altering the flow of water. However, these dams not only slow down the movement of water, but they spread and store water in a way that is much more efficient than human-made dams. In addition, they slow and spread sediment and nutrients as they move through watersheds. What this does is create a mosaic of habitats across a landscape, both aquatic and terrestrial. More habitats lead to more species, both for plants and animals. In this way, beavers create ecosystems, one stick at a time. (Image by NeexPix (Public domain))

    An ecosystem is a community of organisms (biotic components) and their abiotic (non-living) environment. Ecosystems can be small, such as the tide pools found near the rocky shores of many oceans, or large, such as those found in the tropical rainforest of the Amazon in Brazil (figure \(\PageIndex{a}\)).

    A rocky tide pool with seaweed and snails (left) and the Amazon rain forest (right).

    Figure \(\PageIndex{a}\): A (a) tidal pool ecosystem in Matinicus Island, Maine, is a small ecosystem, while the (b) Amazon rainforest in Brazil is a large ecosystem. (credit a: modification of work by Jim Kuhn; credit b: modification of work by Ivan Mlinaric)

    Ecosystem Categories

    There are three broad categories of ecosystems based on their general environment: freshwater, marine, and terrestrial. Within these three categories are individual ecosystem types based on the environmental habitat and organisms present.

    Freshwater ecosystems are the least common, occurring on only 1.8 percent of Earth’s surface. These systems comprise lakes, rivers, streams, and springs; they are quite diverse and support a variety of animals, plants, fungi, protists and prokaryotes.

    Marine ecosystems are the most common, comprising 75 percent of Earth’s surface and consisting of three basic types: shallow ocean, deep ocean water, and deep ocean bottom. Shallow ocean ecosystems include extremely biodiverse coral reef ecosystems. Small photosynthetic organisms suspended in ocean waters, collectively known as phytoplankton, perform 40 percent of all photosynthesis on Earth. Deep ocean bottom ecosystems contain a wide variety of marine organisms. These ecosystems are so deep that light is unable to reach them. Freshwater and marine ecosystems are found in aquatic biomes, which are discussed in the Biomes chapter.

    Terrestrial ecosystems, also known for their diversity, are grouped into large categories called biomes. A biome is a large-scale community of organisms, primarily defined on land by the dominant plant types that exist in geographic regions of the planet with similar climatic conditions. Examples of biomes include tropical rainforests, savannas, deserts, grasslands, temperate forests, and tundras. Grouping these ecosystems into just a few biome categories obscures the great diversity of the individual ecosystems within them. For example, the saguaro cacti (Carnegiea gigantean) and other plant life in the Sonoran Desert, in the United States, are relatively diverse compared with the desolate rocky desert of Boa Vista, an island off the coast of Western Africa (figure \(\PageIndex{b}\)).

    Saguaro cacti that look like telephone poles with arms extended from them (a) and a barren plain of red soil littered with rocks (b).

    Figure \(\PageIndex{b}\): Desert ecosystems, like all ecosystems, can vary greatly. The desert in (a) Saguaro National Park, Arizona, has abundant plant life, while the rocky desert of (b) Boa Vista island, Cape Verde, Africa, is devoid of plant life. (credit a: modification of work by Jay Galvin; credit b: modification of work by Ingo Wölbern)

    Ecosystem Dynamics

    Ecosystems are complex with many interacting parts. They are routinely exposed to various disturbances, or changes in the environment that affect their compositions: yearly variations in rainfall and temperature and the slower processes of plant growth, which may take several years. Many of these disturbances are a result of natural processes. For example, when lightning causes a forest fire and destroys part of a forest ecosystem, the ground is eventually populated by grasses, then by bushes and shrubs, and later by mature trees, restoring the forest to its former state. The impact of environmental disturbances caused by human activities is as important as the changes caused by natural processes. Human agricultural practices, air pollution, acid rain, global deforestation, overfishing, eutrophication, oil spills, and illegal dumping on land and into the ocean are all issues of concern to conservationists.

    Equilibrium is the steady state of an ecosystem where all organisms are in balance with their environment and with each other. In ecology, two parameters are used to measure changes in ecosystems: resistance and resilience. The ability of an ecosystem to remain at equilibrium in spite of disturbances is called resistance. The speed at which an ecosystem recovers equilibrium after being disturbed, called its resilience. Ecosystem resistance and resilience are especially important when considering human impact. The nature of an ecosystem may change to such a degree that it can lose its resilience entirely. This process can lead to the complete destruction or irreversible altering of the ecosystem.

    Foundation Species

    Foundation species are considered the “base” or “bedrock” of an ecosystem, having the greatest influence on its overall structure. They are often primary producers, and they are typically an abundant organism. For example, kelp, a species of brown algae, is a foundation species that forms the basis of the kelp forests off the coast of California.

    Foundation species may physically modify the environment to produce and maintain habitats that benefit the other organisms that use them. Examples include the kelp described above or tree species found in a forest. The photosynthetic corals of the coral reef also provide structure by physically modifying the environment (figure \(\PageIndex{c}\)). The calcium carbonate deposits of living and dead coral make up most of the reef structure, which protects many other species from waves and ocean currents.

    A coral reef, consisting of branching and brightly colored coral submerged in water

    Figure \(\PageIndex{c}\): Coral is the foundation species of coral reef ecosystems. (credit: Jim E. Maragos, USFWS)


    Modified by Melissa Ha from the following sources:

    This page titled 5.1: Ecosystem Types and Dynamics is shared under a CC BY-NC license and was authored, remixed, and/or curated by Melissa Ha and Rachel Schleiger (ASCCC Open Educational Resources Initiative) .