Universität Bielefeld

Ecosystems

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An ecosystem (from the old greek words οἶκος (house) and σύστημα (system) is defined as the community of all living (biotic) organisms (biocoenosis) and their non-living (abiotic) environment (biotope or habitat) including the manifold interactions among all these components. According to this definition, ecosystems can be of any size from the microscale to the entire globe.

The basic idea, that organisms and their habitat represent a common entity, was born in the 19th century, when the British physiologist John Scott Haldane (1860-1936) wrote, that the parts of an organism and its environment represent a connected system. Independently, the term „ecosystem“, was coined in 1935 by the British biologist and geobotanist Arthur George Tansley, who worked on transfers between organisms and their environment. In his famous article “The use and abuse of vegetational terms and concepts" he wrote: “Though the organisms may claim our prime interest, when we are trying to think fundamentally, we cannot separate them from their special environments, with which they form one physical system”.

All organisms of an ecosystem consist of biomass, containing a variety of inorganic substances (mainly carbon, nitrogen, water and minerals) and energy. The inorganic substances are taken from respective pools of limited size in the biotope. The energy comes primarily from the sun. The reaction which captures solar energy and makes it available for organisms is called photosynthesis. All green plants are able to photosynthesize, i.e. absorb solar energy with a special pigment system (chlorophyll) and use this energy to build up organic biomass (mainly carbohydrates) from inorganic atmospheric carbon dioxide, water and some mineral nutrients. This process is called primary production and plants are primary producers. All other, non-green organisms (mainly animals) need to obtain the necessary solar energy for building up their own biomass by feeding on green plants or on each other. Additionally, they have to take up water and nutrients from their abiotic environment. These organisms are called consumers. All green and non-green organisms utilize the absorbed or consumed solar energy partially for building up their own biomass and partially for their metabolism, i.e. for enzymatically breaking down (i.e. oxidizing) energy rich biomass components like carbohydrates. This process is called respiration. When organisms die, their biomass is broken down (or mineralized) by a group of organisms called decomposers (mainly fungi and bacteria), which recycle the contained inorganic substances into their respective pools, where they can be used again by newly developing organisms (circular flux of matter). However, the solar energy contained in a piece of biomass is converted step by step into heat and released into outer space on its way from the primary producers to the decomposers.

Ecosystems are not static, but rather dynamic entities. During undisturbed ecosystem development various biocenoses typically follow upon each other in a defined regular way causing concomitant changes in the abiotic parts of the system. This developmental process is called succession. If a final stage is reached at all, it is typically a very dynamic equilibrium, but normally the course of succession is continuously affected by natural and anthropogenic disturbances at all scales (e.g. storms, volcano eruptions, immigration, or introduction or removal of species). Depending on the severity and the spatial and temporal extent of such disturbances, the course of succession may be changed or even reverted. In many cases ecosystems can respond flexibly, return to the normal successional process and recover. However, if the species’ composition of the biocoenosis is altered (i.e. if biodiversity is affected), or the abiotic conditions are changed beyond certain thresholds, the course of succession may change into a new direction. Such changes are frequently irreversible.

Ecosystems offer numerous essential services for humanity, like the supply of food, construction material, medical drugs, crop pollination and most importantly, a large gene pool, which can be used to improve the performance of domestic species. Furthermore, ecosystems maintain hydrological cycles and atmospheric oxygen concentration. They provide clean air and water, and even things like beauty, inspiration, and recreational opportunities.

Despite of all the scientific progress in ecological research, we must admit that - with very few exceptions - the extremely complex interaction network between the components of typical ecosystems is still far from being understood. Thus, at present, the prediction of potential consequences of anthropogenic disturbances is difficult, if not impossible, and unexpected and unwanted effects do frequently occur. Since humans are part of their ecosystems and strongly depend on their various products and services, care should be taken in handling such delicate and multidimensional networks.

Examples of a North American Ecosystem

Taiga

An ecosystem exclusive to North America (Fischer, 1995) is the predominantly forested taiga (from the Russian word “тайга”, which means “dense, marshy forest”). Also known as boreal forest or snow forest, it is located roughly north of 50 °N latitude spanning over a wide geographical area from Alaska through basically all of Canada’s inland and reaching into the northern continental USA (Oechel & Lawrence, 1985). The Northern limit of the taiga is the tree line in the Arctic, the line beyond which trees are not capable of growing anymore due to intolerable environmental conditions, such as permafrost soil and extremely low moisture. With annual mean temperatures well below 0 °C in many areas of the taiga, it can be considered a very cold ecosystem.

Worldwide, the taiga is the largest connected land biome constituting roughly 1.4 billion ha of forest or 29 % of the world’s forest cover (see “Taiga biological station”). Economically, this ecosystem is the world’s most important forest region. However, the taiga also plays a major role in global CO2 and CH4 cycles – probably storing more than twice as much carbon per unit area as tropical forests. Predictions place the taiga at latitudes that will be affected the most by global warming (Ruckstuhl et al., 2008).

North America contains the largest undisturbed taiga area of the world. It can be found between the Canadian Yukon Territory and the middle course of the Yukon River in Alaska. The humid and cold climate of the taiga led to a characteristic flora and fauna containing a total of approximately 20,300 thus far identified species (Ruckstuhl et al. 2008). Dominant plants in this area are coniferous trees, such as larch, spruce, fir, and pine, but deciduous trees, such as birch, aspen, and willow can also be found. Understory plants are mainly present in the form of ferns, dwarf shrubs such as Vaccinium berries (blueberries, cranberries, etc.) and some grasses, while lichens and mosses are wide-spread, too. Due to the rather extreme climate, the taiga is home to relatively few but rather iconic animals. Among them are the moose (Alces alces), caribou (Rangifer tarandus), and brown bear (Ursus arctos).

Examples of South American Ecosystems

Almost 7500 km long and 5000 km wide, the South American continent spans from the tropical zone all the way to subarctic areas. With elevations of close to 7000 m, this continent constitutes a highly diverse zonation regarding climate as well as plant and animal communities. As examples, two of the most notable ecosystems are shortly characterized below.

Tropical rain forests

South America contains the largest connected equatorial rain forests in the world, located mainly in Brazil, Colombia, Ecuador, and Peru. Naturally, ecosystems are not confined by political borders, but by geological and climatic conditions. This of course also applies to tropical rain forests. A good example is the Amazonas basin, which borders Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, and Venezuela while forming its own ecological entity mainly consisting of tropical rain forest and several limnic systems.

The main climatic characteristics of rainforests are high temperature, high precipitation, high air humidity (close to 100%), and a missing or only moderate climatic seasonality. Mean monthly temperatures are typically between 25°C and 27 °C throughout the entire year. The average annual precipitation ranges from between 2000 mm to 4000 mm compared to Middle European annual averages of air temperature and precipitation between 8°C and 10°C and 400-800 mm respectively; this results in a highly productive ecosystem dominated by tall trees with a vegetation period that spans all 12 months. 1 ha of tropical rain forest contains a biomass of 400 to 800 tons dry weight of which animals constitute only a very small fraction (in the O/OO range). Species diversity in these forest ecosystems is spectacular. Up to 600 tree species and about 1000 total plant species occur per ha. There are, for instance, more ant species on a single tree individual in Peru than in all of Great Britain and more than 3000 beetle species were found in just five single tree crowns (Grabherr, 1997).

Páramo

Another paradigmatically interesting ecosystem is the Páramo, which is located above the continuous forest, line but below the permanent snow line (around 3000 to 4700 m). It can be found in the northwest corner of South America, mainly in Colombia, but also in Venezuela, Peru, and Ecuador. Although located in the tropical climate zone, the Páramo looks more like a Tundra ecosystem, which is a result of the very special climatic conditions at these altitudes. Just like the tropical rain forest, the Páramo possesses a diurnal rather than a seasonal climate. However, the diurnal temperature variations can be extreme: In some places, temperatures can be as high as 30 °C during the day, but often well below freezing, especially during the early morning hours (sometimes referred to as “summer every day and winter every night”). Mean annual air temperatures are between 2 °C and 10 °C depending on elevation and latitude. Average annual precipitation ranges from 1000 mm up to 2000 mm. While the solar radiation in these altitudes is exceptionally high, fog is frequent. This wet and temperature-wise varying climate in combination with variations in solar radiation results in rather harsh conditions for living organisms, which in turn led to the evolution of very interesting and unique adaption mechanisms particularly in plants.

Typical examples are giant rosette plants (Espeletia sp.) with woolly-hairy, succulent leaves. While the hair on the plants reflect the intense sun light, the leaf tissue contains special osmotica, which serve as natural antifreeze agents by reducing the freezing point of the cell sap. The dead leaves of former years remain on the plant and form a coat, which isolates the living tissues of the trunk against temperature extremes. The living leaves form a rosette at the top of the trunk far away from the extreme temperatures near the soil surface. Most of the neighboring plant and moss species look brown or yellowish instead of green because they contain high amounts of special pigments, which protect their cells from the naturally occurring high UV-B radiation.

Several iconic animals are native to the Páramo, like the spectacled bear (Tremarctos ornatus), the Andean condor (Vultur gryphus), and the Andean fox (Lycalopex culpaeus). However, species diversity is significantly lower in this ecosystem than in the aforementioned tropical rain forest.

Wolfram Beyschlag, Alexander Mosena


Please cite as:
Beyschlag, Wolfram and Alexander Mosena. 2015. “Ecosystems.” InterAmerican Wiki: Terms - Concepts - Critical Perspectives. www.uni-bielefeld.de/cias/wiki/e_Ecosystems.html.


Bibliography

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Taiga biological station, obtained 22.10.2015. FAQ: http://www.wilds.mb.ca/taiga/tbsfaq.html Tansley, A.G. (1935) The use and abuse of vegetational terms and concepts. Ecology 16: 284-307

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