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The balance of nature, also known as ecological balance, is a theory that proposes that ecological systems are usually in a stable equilibrium or homeostasis, which is to say that a small change (the size of a particular population, for example) will be corrected by some negative feedback that will bring the parameter back to its original "point of balance" with the rest of the system.
For example, among aquatic ecosystems, higher rates of production are usually found in large rivers and shallow lakes than in deep lakes and clear headwater streams. [25] Among terrestrial ecosystems, marshes, swamps, and tropical rainforests have the highest primary production rates, whereas tundra and alpine ecosystems have the lowest. [25]
A freshwater aquatic food web. The blue arrows show a complete food chain (algae → daphnia → gizzard shad → largemouth bass → great blue heron). A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community.
The term "ecosystem" was first used in 1935 in a publication by British ecologist Arthur Tansley. The term was coined by Arthur Roy Clapham , who came up with the word at Tansley's request. [ 6 ] Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.
Typical units are grams per square meter, or calories per square meter. The pyramid of biomass may be "inverted". For example, in a pond ecosystem, the standing crop of phytoplankton, the major producers, at any given point will be lower than the mass of the heterotrophs, such as fish and insects.
The economic activity of pollination alone represented between $2.1–14.6 billion in 2003. [146] Other sources have reported somewhat conflicting results and in 1997 Robert Costanza and his colleagues reported the estimated global value of ecosystem services (not captured in traditional markets) at an average of $33 trillion annually. [147]
Like other ecosystems, agroecosystems form partially closed systems in which animals, plants, microbes, and other living organisms and their environment are interdependent and regularly interact. They are somewhat arbitrarily defined as a spatially and functionally coherent unit of agricultural activity.
Lake ecosystems can be divided into zones. One common system divides lakes into three zones. The first, the littoral zone, is the shallow zone near the shore. [5] This is where rooted wetland plants occur. The offshore is divided into two further zones, an open water zone and a deep water zone.