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From Wikipedia, the free encyclopedia

Food chain in a Swedish lake. Osprey feed on northern pike, which in turn feed on perch which eat bleak which eat crustaceans
Food chain in a Swedish lake. Osprey feed on northern pike, which in turn feed on perch which eat bleak which eat crustaceans

A food chain is a linear network of links in a food web starting from producer organisms (such as grass or trees which use radiation from the Sun to make their food) and ending at an apex predator species (like grizzly bears or killer whales), detritivores (like earthworms or woodlice), or decomposer species (such as fungi or bacteria). A food chain also shows how organisms are related to each other by the food they eat. Each level of a food chain represents a different trophic level. A food chain differs from a food web because the complex network of different animals' feeding relations are aggregated and the chain only follows a direct, linear pathway of one animal at a time. Natural interconnections between food chains make it a food web.

A common metric used to quantify food web trophic structure is food chain length. In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web. The mean chain length of an entire web is the arithmetic average of the lengths of all chains in the food web.[1][2] The food chain is an energy source diagram. The food chain begins with a producer, which is eaten by a primary consumer. The primary consumer may be eaten by a secondary consumer, which in turn may be consumed by a tertiary consumer. For example, a food chain might start with a green plant as the producer, which is eaten by a snail, the primary consumer. The snail might then be the prey of a secondary consumer such as a frog, which itself may be eaten by a tertiary consumer such as a snake.

Food chains are very important for the survival of most species. When only one element is removed from the food chain it can result in extinction of a species in some cases. The foundation of the food chain consists of primary producers. Primary producers, or autotrophs, utilize energy derived from either sunlight or inorganic chemical compounds to create complex organic compounds, whereas species at higher trophic levels cannot and so must consume producers or other life that itself consumes producers. Because the sun's light is necessary for photosynthesis, most life could not exist if the sun disappeared. Even so, it has recently been discovered that there are some forms of life, chemotrophs, that appear to gain all their metabolic energy from chemosynthesis driven by hydrothermal vents, thus showing that some life may not require solar energy to thrive.

Decomposers, which feed on dead animals, break down the organic compounds into simple nutrients that are returned to the soil. These are the simple nutrients that plants require to create organic compounds. It is estimated that there are more than 100,000 different decomposers in existence.

Many food webs have a keystone species. A keystone species is a species that has a large impact on the surrounding environment and can directly affect the food chain. If this keystone species dies off it can set the entire food chain off balance. Keystone species keep herbivores from depleting all of the foliage in their environment and preventing mass extinction.[3]

Food chains were first introduced by the Arab scientist and philosopher Al-Jahiz in the 10th century and later popularized in a book published in 1927 by Charles Elton, which also introduced the food web concept.[4][5][6]

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Transcription

We all know about the dinosaurs that once roamed the planet, but long after they went extinct, great beasts we call the megafauna lived on every continent. In the Americas, ground sloths the size of elephants pulled down trees with their claws. Saber-toothed cats the size of brown bears hunted in packs, but they were no match for short-faced bears, which stood thirteen feet on their hind legs, and are likely to have driven these cats away from their prey. There were armadillos as big as small cars, an eight foot beaver, and a bird with a 26 foot wingspan. Almost everywhere, the world's megafauna were driven to extinction, often by human hunters. Some species still survive in parts of Africa and Asia. In other places, you can still see the legacy of these great beasts. Most trees are able to resprout where their trunk is broken to withstand the loss of much of their bark and to survive splitting, twisting and trampling, partly because they evolved to survive attacks by elephants. The American pronghorn can run so fast because it evolved to escape the American cheetah. The surviving animals live in ghost ecosystems adapted to threats from species that no longer exist. Today, it may be possible to resurrect those ghosts, to bring back lost species using genetic material. For instance, there's been research in to cloning woolly mammoths from frozen remains. But even if it's not possible, we can still restore many of the ecosystems the world has lost. How? By making use of abandoned farms. As the market for food is globalized, infertile land becomes uncompetitive. Farmers in barren places can't compete with people growing crops on better land elsewhere. As a result, farming has started to retreat from many regions, and trees have started to return. One estimate claims that two-thirds of land in the US that was once forested but was cleared for farming has become forested again. Another estimate suggests that by 2030, an area in Europe the size of Poland will be vaccated by farmers. So even if we can't use DNA to bring back ground sloths and giant armadillos, we can restore bears, wolves, pumas lynx, moose and bison to the places where they used to live. Some of these animals can reshape their surroundings, creating conditions that allow other species to thrive. When wolves were reintroduced to the Yellowstone National Park in 1995, they quickly transformed the ecosystem. Where they reduced the numbers of overpopulated deer, vegetation began to recover. The height of some trees quintupled in just six years. As forests returned, so did songbirds. Beavers, which eat trees, multiplied in the rivers, and their dams provided homes for otters, muskrats, ducks, frogs and fish. The wolves killed coyotes, allowing rabbits and mice to increase, providing more food for hawks, weasels, foxes and badgers. Bald eagles and ravens fed on the carrion that the wolves abandoned. So did bears, which also ate the berries on the returning shrubs. Bison numbers rose as they browsed the revitalized forests. The wolves changed almost everything. This is an example of a trophic cascade, a change at the top of the food chain that tumbles all the way to the bottom, affecting every level. The discovery of widespread trophic cascades may be one of the most exciting scientific findings of the past half century. They tell us that ecosystems that have lost just one or two species of large animals can behave in radically different ways from those that retain them. All over the world, new movements are trying to catalyze the restoration of nature in a process called rewilding. This means undoing some of the damage we've caused, reestablishing species which have been driven out, and then stepping back. There is no attempt to create an ideal ecosystem, to produce a heath, a rainforest or a coral reef. Rewilding is about bringing back the species that drive dynamic processes and then letting nature take its course. But it's essential that rewilding must never be used as an excuse to push people off the land. It should happen only with the consent and enthusiasm of the people who work there. Imagine standing on a cliff in England, watching sperm whales attacking shoals of herring as they did within sight of the shore until the 18th century. By creating marine reserves in which no commerical fishing takes place, that can happen again. Imagine a European Serengeti full of the animals that used to live there: hippos, rhinos, elephants, hyenas and lions. What rewilding reintroduces, alongside the missing animals and plants, is that rare species called hope. It tells us that ecological change need not always proceed in the same direction. The silent spring could be followed by a wild summer.

Food chain length

This food web of waterbirds from Chesapeake Bay is a network of food chains
This food web of waterbirds from Chesapeake Bay is a network of food chains

The length of a food chain is a continuous variable providing a measure of the passage of energy and an index of ecological structure that increases through the linkages from the lowest to the highest trophic (feeding) levels.[7]

Food chains are directional paths of trophic energy or, equivalently, sequences of links that start with basal species, such as producers or fine organic matter, and end with consumer organisms.[8]:370

Food chains are often used in ecological modeling (such as a three-species food chain). They are simplified abstractions of real food webs, but complex in their dynamics and mathematical implications.[9]

Ecologists have formulated and tested hypotheses regarding the nature of ecological patterns associated with food chain length, such as increasing length increasing with ecosystem size, reduction of energy at each successive level, or the proposition that long food chain lengths are unstable.[7] Food chain studies have an important role in ecotoxicology studies, which trace the pathways and biomagnification of environmental contaminants.[10]

Producers, such as plants, are organisms that utilize solar or chemical energy to synthesize starch. All food chains must start with a producer. In the deep sea, food chains centered on hydrothermal vents and cold seeps exist in the absence of sunlight. Chemosynthetic bacteria and archaea use hydrogen sulfide and methane from hydrothermal vents and cold seeps as an energy source (just as plants use sunlight) to produce carbohydrates; they form the base of the food chain. Consumers are organisms that eat other organisms. All organisms in a food chain, except the first organism, are consumers.[citation needed]

Food chain length is important because the amount of energy transferred decreases as trophic level increases; generally only ten percent of the total energy at one trophic level is passed to the next, as the remainder is used in the metabolic process. There are usually no more than five tropic levels in a food chain.[11] Humans are able to receive more energy by going back a level in the chain and consuming the food before, for example getting more energy per pound from consuming a salad than an animal which ate lettuce.[12][13] However, this does not work in all cases. For example, humans do not have the ability to directly digest grass or the nutrients from wild plants but can naturally obtain these nutrients by (killing and) consuming the meat from deer, antelope, or other grass-eating animals. Food chains are very important for the survival of most species. When only one element is removed from the food chain it can result in the extinction of a species in some cases.

The efficiency of a food chain depends on the energy first consumed by the primary producers.[13] The primary consumer gets its energy from the producer. The tertiary consumer is the 3rd consumer, it is placed at number four in the food chain. Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer.

See also

Earth Day Flag.png Ecology portal

References

  1. ^ Briand, F.; Cohen, J. E. (1987). "Environmental correlates of food chain length" (PDF). Science. 238 (4829): 956–960. Bibcode:1987Sci...238..956B. doi:10.1126/science.3672136. PMID 3672136. Archived from the original (PDF) on 2012-04-25.
  2. ^ Post, D. M.; Pace, M. L.; Haristis, A. M. (2006). "Parasites dominate food web links". Proceedings of the National Academy of Sciences. 103 (30): 11211–11216. Bibcode:2006PNAS..10311211L. doi:10.1073/pnas.0604755103. PMC 1544067. PMID 16844774.
  3. ^ "The Food Chain". www2.nau.edu. Retrieved 2019-05-04.
  4. ^ Elton, C. S. (1927). Animal Ecology. London, UK.: Sidgwick and Jackson. ISBN 0-226-20639-4.
  5. ^ Allesina, S.; Alonso, D.; Pascal, M. (2008). "A general model for food web structure" (PDF). Science. 320 (5876): 658–661. Bibcode:2008Sci...320..658A. doi:10.1126/science.1156269. PMID 18451301. S2CID 11536563. Archived from the original (PDF) on 2016-05-15.
  6. ^ Egerton, F. N. (2007). "Understanding food chains and food webs, 1700-1970". Bulletin of the Ecological Society of America. 88: 50–69. doi:10.1890/0012-9623(2007)88[50:UFCAFW]2.0.CO;2.
  7. ^ a b Vander Zanden, M. J.; Shuter, B. J.; Lester, N.; Rasmussen, J. B. (1999). "Patterns of food chain length in lakes: A stable isotope study" (PDF). The American Naturalist. 154 (4): 406–416. doi:10.1086/303250. PMID 10523487. S2CID 4424697.
  8. ^ Martinez, N. D. (1991). "Artifacts or attributes? Effects of resolution on the Little Rock Lake food web" (PDF). Ecological Monographs. 61 (4): 367–392. doi:10.2307/2937047. JSTOR 2937047.
  9. ^ Post, D. M.; Conners, M. E.; Goldberg, D. S. (2000). "Prey preference by a top predator and the stability of linked food chains" (PDF). Ecology. 81: 8–14. doi:10.1890/0012-9658(2000)081[0008:PPBATP]2.0.CO;2.
  10. ^ Odum, E. P.; Barrett, G. W. (2005). Fundamentals of ecology. Brooks/Cole. p. 598. ISBN 978-0-534-42066-6.
  11. ^ Wilkin, Douglas; Brainard, Jean (2015-12-11). "Food Chain". CK-12. Retrieved 2019-11-06.
  12. ^ Rafferty, John P.; et al. (Kara Rogers, Editors of Encyclopædia Britannica). "Food chain". Food chain | Definition, Types, & Facts. Encyclopædia Britannica. Retrieved 2019-10-25.
  13. ^ a b Rowland, Freya E.; Bricker, Kelly J.; Vanni, Michael J.; González, María J. (2015-04-13). "Light and nutrients regulate energy transfer through benthic and pelagic food chains". Oikos. Nordic Foundation Oikos. 124 (12): 1648–1663. doi:10.1111/oik.02106. ISSN 1600-0706. Retrieved 2019-10-25 – via ResearchGate.
This page was last edited on 19 July 2021, at 08:42
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