Ecosystem Structure and Function
Ecosystem components (structure)
Ecosystems might be observed in a lot of ways, so there isn’t a set of components which make up an ecosystem. However, all ecosystems have to include both abiotic and biotic components, the interactions, and a known source of energy. The simplest but least representative of ecosystems therefore contains just one living plant – the biotic component, in a small terrarium with light exposure to which water source with essential nutrients for the plant’s growth has been added – the abiotic environment. The other extreme is the biosphere, which has all of Earth's organisms and the interactions between them and Earth’s systems – the abiotic environment. And of course, the majority of ecosystems fall in between the extremes of complexity.
At a core functional level, ecosystems normally contain primary producers able to harvest energy from sunlight by photosynthesis and to use the energy to turn carbon dioxide with other inorganic chemicals in the organic building blocks of life. The consumers feed upon this captured energy, while decomposers not only feed on the energy, but also break up the organic matter into the inorganic constituents, for them to be used again by the producers. Those interactions among the producers and organisms which consume and decompose are called trophic interactions, composed of trophic levels in the energy pyramid, and the most energy and mass are in the primary producers, at the base, while the higher levels of the pyramid, beginning with the primary consumers that feed on primary producers, the secondary consumers which feed on these, and so forth. Trophic interactions are described in a more detailed form as the food chain, which organizes the specific organisms by the trophic distance from the primary producers, and with food webs, which map the feeding interactions between all the organisms in the ecosystem. Together, the processes of matter cycling and energy transfer are essential in finding out ecosystem function and structure and defining the kinds of interactions between the environment and its organisms. It should also be noted most ecosystems have a wide array of species, and the diversity ought to be considered part and parcel of the ecosystem structure.
Ecosystem processes (function)
By definition, all ecosystems cycle matter and use energy, and the processes define the fundamental ecosystem functions as well. Energetic processes in an ecosystem are normally described by speaking of trophic levels that define the position of organisms according to their level of feeding in comparison to the original energy taken in by primary producers. Always the energy doesn’t cycle and ecosystems need a continuous inflow of high-quality energy in order to maintain their function and structure. For this reason, ecosystems are "open systems" needing a net inflow of energy to continue over time - without the sun, our biosphere would shortly run out of energy!
Energy inputs to ecosystems drive the flow of matter within organisms and their environment in a process called biogeochemical cycling. Our biosphere gives a good example of the process, as it exchanges matter with and interacts with the lithosphere, atmosphere and hydrosphere, driving the Earth’s biogeochemical cycles of nitrogen, phosphorus, sulfur, carbon and the other elements. An ecosystem process is dynamic, undergoing strong seasonal cycles responding to changes in the solar irradiation; causing fluctuations in the primary productivity; varying the inflow of energy from photosynthesis and carbon dioxide fixation ointo organic materials during the year; driving remarkable annual diversity in the carbon cycle, which is the biggest of all global biogeochemical cycles. The fixed organic carbon in plants becomes then food for decomposers and consumers, who degrade this carbon into forms with less energy, and finally releasing this photosynthesis-fixed carbon back into carbon dioxide in our atmosphere, creating the global carbon cycle. The nitrogen biogeochemical cycling also uses energy, because bacteria fix the nitrogen gas from the atmosphere in reactive forms useful to living organisms with energy from organic materials or from the sun and from plants. Ecosystems cycle sulfur, phosphorus and other elements as well. Because biogeochemical cycles are determined by the transfer of matter between the environment and its organisms, they are good examples of ecosystem-level processes.