An ecosystem is a community made up of living organisms and nonliving components such as air, water and mineral soil, all interacting as a system. (However, ecosystems can be defined in many ways.) The biotic and abiotic components interact through nutrient cycles and energy flows. Ecosystems are the network of interactions among organisms, and between organisms and their environment. Ecosystems can be of any size but one ecosystem has a specific, limited space. On a larger scale, some scientists view the entire planet as one ecosystem).

Energy, water, nitrogen and soil minerals are other essential abiotic components of an ecosystem. The energy that flows through ecosystems comes primarily from the sun, through photosynthesis. Photosynthesis also captures carbon dioxide from the atmosphere. Animals also play an important role in the movement of matter and energy through eooystems. They influence the amount plant and microbial biomass that lives in the system. As organic matter dies, decomposers release carbon back to the atmosphere. This process also facilitates nutrient cycling by converting nutrients stored in dead biomass back to a form that can be used again by plants and other microbes.

Ecosystems are controlled both by external and internal factors. External factors such as climate, the parent material that forms the soil, topography and time have a big impact on ecosystems, but they are not themselves influenced by the ecosystem. Ecosystems are dynamic: they are subject to periodic disturbances and are in the process of recovering from past disturbance. Internal factors not only control ecosystem processes but are also controlled by them. Internal factors are subject to feedback loops. The resource inputs are generally controlled by external processes like climate and parent material. The availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Other internal factors include disturbance, succession and the types of species present. Biodiversity affects ecosystem function.

Humans operate within ecosystems and the cumulative effects of human activities can influence even external factors. Climate change is an example of that cumulative impact. Ecosystems provide a variety of goods and services upon which people depend. Ecosystem management suggests that rather than managing individual species, natural resources should be managed at the level of the ecosystem itself. Ecosystem services are in many cases threatened by human activities.

There is no single definition of what constitutes an ecosystem. German ecologist Ernst-Detlef Schulze and coauthors defined an ecosystem as an area which is "uniform regarding the biological turnover, and contains all the fluxes above and below the ground area under consideration." They explicitly reject Gene Likens' use of entire river catchments as "too wide a demarcation" to be a single ecosystem, given the level of heterogeneity within such an area. Other authors have suggested that an ecosystem can encompass a much larger area, even the whole planet. Schulze and coauthors also rejected the idea that a single rotting log could be studied as an ecosystem because the size of the flows between the log and its surroundings are too large, relative to the proportion cycles within the log. Philosopher of science Mark Sagoff considers the failure to define "the kind of object it studies" to be an obstacle to the development of theory in ecosystem ecology.

Ecosystems can be studied through a variety of approaches—theoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation. Studies can be carried out at a variety of scales, from microcosms and mesocosms which serve as simplified representations of ecosystems, through whole-ecosystem studies. American ecologist Stephen R. Carpenter has argued that microcosm experiments can be "irrelevant and diversionary" if they are not carried out in conjunction with field studies carried out at the ecosystem scale, because microcosm experiments often fail to accurately predict ecosystem-level dynamics.

The Hubbard Brook Ecosystem Study, established in the White Mountains, New Hampshire in 1963, was the first successful attempt to study an entire watershed as an ecosystem. The study used stream chemistry as a means of monitoring ecosystem properties, and developed a detailed biogeochemical model of the ecosystem. Long-term research at the site led to the discovery of acid rain in North America in 1972, and was able to document the consequent depletion of soil cations (especially calcium) over the next several decades.

The term "ecosystem" is often used very imprecisely and linked with a descriptive term (adjective) even if those systems are rather biomes, not ecosystems. Examples include: terrestrial ecosystem or aquatic ecosystems. Aquatic ecosystems are split into marine ecosystems (Large marine ecosystem is another term used) and freshwater ecosystems.

This page was last edited on 20 March 2018, at 23:21.
Reference: under CC BY-SA license.

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