An ecosystem (short for "ecological system") is generally defined as a community of organisms living in a particular environment and the physical elements with which they interact. An ecosystem is an open functional unit that results from the interactions of abiotic (soil, water, light, inorganic nutrients and weather), biotic (plants, animals, and microorganisms usually categorized as either producers or consumers), and cultural (anthropogenic) components.
An ecosystem can be as small as a field or as large as the ocean. It is used to describe the world’s major different habitat types. Terrestrial ecosystems include: arctic and alpine ecosystems, dominated by tundra with scarce vegetation; forest ecosystems, which can be subdivided into a whole range of types including tropical rainforests, Mediterranean evergreen forests, boreal forests, and temperate coniferous, deciduous and mixed forests; grasslands and savannas; and deserts and semi-arid ecosystems. Freshwater ecosystems include lakes, rivers, and marshlands. Marine ecosystems comprise an enormous range, from coral reefs, mangroves, sea-grass beds, and other shallow coastal water ecosystems, to open-water ones, including the mysterious, little-known ecosystems of the abyssal plains and trenches of the world’s oceans.
Ecosystems sustain human societies and allow them to prosper, due to the nutritional, environmental, cultural, recreational and aesthetic resources they provide. We all depend directly or indirectly on the products and services of ecosystems, including crops, livestock, fish, wood, clean water, oxygen, and wildlife.
Climate is an integral part of ecosystems. Climate change has the potential to stress or even alter ecosystems and their functions, including the many resources and services they provide to each other and to our society. Some organisms may be able to adapt to new conditions, but some may not be able to keep up with the changes. Climate change could benefit certain plant or insect species by increasing their ranges, but could be also an eliminating factor for those species that lose their natural habitat. The risk of extinction could increase for many species, especially those that are already endangered or at risk due to geographic isolation caused by natural drift or by human development. Other risk factors include decreasing population numbers for certain species, or a narrow temperature tolerance range. Human activities can pose a threat to biodiversity by altering habitats or introducing non-native species. Climate change and various anthropogenic activities are causing large losses to natural habitats and wildlife in both developed and developing countries.
According to the Fourth Assessment of the IPCC, there is a high confidence that the resilience of many ecosystems (their ability to adapt naturally) in the 21st century will be exceeded by an unprecedented combination of several factors, including change in climate, increased frequency of major disturbances such as flooding, drought and wildfire, an increasing rate of biological invasions, and ocean acidification due to high carbon dioxide levels.
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