Detritus

In biology, detritus (/dɪˈtraɪtəs/) is dead particulate organic material (as opposed to dissolved organic material). It typically includes the bodies or fragments of dead organisms as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose (or remineralize) the material. In terrestrial ecosystems, it is encountered as leaf litter and other organic matter intermixed with soil, which is denominated "soil organic matter". Detritus of aquatic ecosystems is organic material suspended in water and piling up on seabed floors, which is referred to as marine snow.

Horse Manure and Hay Detritus
Horse feces and hay – detritus used as manure

Theory

Sequoiadendron giganteum 08130
Giant sequoia (Sequoiadendron giganteum) cones and foliage, sugar pine and white fir foliage, and other plant litter cover the floor of Mariposa Grove in Yosemite National Park.

Dead plants or animals, material derived from animal tissues (such as skin cast off during moulting etc) gradually lose their form, due to both physical processes and the action of decomposers, including grazers, bacteria and fungi. Decomposition, the process through which organic matter is decomposed, takes place in many stages. Materials like proteins, lipids and sugars with low molecular weight are rapidly consumed and absorbed by microorganisms and organisms that feed on dead matter. Other compounds, such as complex carbohydrates are broken down more slowly. The various microorganisms involved in the decomposition break down the organic materials in order to gain the resources they require for their own survival and proliferation. Accordingly, at the same time that the materials of plants and animals are being broken d(biomass) making up the bodies of the microorganisms are built up by a process of assimilation. When microorganisms die, fine organic particles are produced, and if these are eaten by small animals which feed on microorganisms, they will collect inside the intestine, and change shape into large pellets of dung. As a result of this process, most of the materials from dead organisms disappears from view and is not obviously present in any recognisable form, but is in fact present in the form of a combination of fine organic particles and the organisms using them as nutrients. This combination is detritus.

In ecosystems on land, detritus is deposited on the surface of the ground, taking forms such as the humic soil beneath a layer of fallen leaves. In aquatic ecosystems, most detritus is suspended in water, and gradually settles. In particular, many different types of material are collected together by currents, and much material settles in slowly flowing areas.

Much detritus is used as a source of nutrition for animals. In particular, many bottom feeding animals (benthos) living in mud flats feed in this way. In particular, since excreta are materials which other animals do not need, whatever energy value they might have, they are often unbalanced as a source of nutrients, and are not suitable as a source of nutrition on their own. However, there are many microorganisms which multiply in natural environments. These microorganisms do not simply absorb nutrients from these particles, but also shape their own bodies so that they can take the resources they lack from the area around them, and this allows them to make use of excreta as a source of nutrients. In practical terms, the most important constituents of detritus are complex carbohydrates, which are persistent (difficult to break down), and the microorganisms which multiply using these absorb carbon from the detritus, and materials such as nitrogen and phosphorus from the water in their environment to synthesise the components of their own cells.

A characteristic type of food chain called the detritus cycle takes place involving detritus feeders (detritivores), detritus and the microorganisms that multiply on it. For example, mud flats are inhabited by many univalves which are detritus feeders. When these detritus feeders take in detritus with microorganisms multiplying on it, they mainly break down and absorb the microorganisms, which are rich in proteins, and excrete the detritus, which is mostly complex carbohydrates, having hardly broken it down at all. At first this dung is a poor source of nutrition, and so univalves pay no attention to it, but after several days, microorganisms begin to multiply on it again, its nutritional balance improves, and so they eat it again. Through this process of eating the detritus many times over and harvesting the microorganisms from it, the detritus thins out, becomes fractured and becomes easier for the microorganisms to use, and so the complex carbohydrates are also steadily broken down and disappear over time.

What is left behind by the detritivores is then further broken down and recycled by decomposers, such as bacteria and fungi.

This detritus cycle plays a large part in the so-called purification process, whereby organic materials carried in by rivers is broken down and disappears, and an extremely important part in the breeding and growth of marine resources. In ecosystems on land, far more essential material is broken down as dead material passing through the detritus chain than is broken down by being eaten by animals in a living state. In both land and aquatic ecosystems, the role played by detritus is too large to ignore.

Aquatic ecosystems

In contrast to land ecosystems, dead materials and excreta in aquatic ecosystems are typically transported by water flow; finer particles tend to be transported farther or suspended longer. In freshwater bodies organic material from plants can form a silt known as mulm or humus on the bottom. This material, some called undissolved organic carbon breaks down into dissolved organic carbon and can bond to heavy metal ions via chelation. It can also break down into colored dissolved organic matter such as tannin, a specific form of tannic acid. In saltwater bodies, organic material breaks down and forms a marine snow that slowly settles down to the ocean bottom.

Terrestrial ecosystems

Detritus occurs in a variety of terrestrial habitats including forest, chaparral and grassland. In forests the detritus is typically dominated by leaf, twig, and bacteria litter as measured by biomass dominance. This plant litter provides important cover for seedling protection as well as cover for a variety of arthropods, reptiles[1] and amphibians. Some insect larvae feed on the detritus.[2] Fungi and bacteria continue the decomposition process[3] after grazers have consumed larger elements of the organic materials, and animal trampling has assisted in mechanically breaking down organic matter. At the later stages of decomposition, mesophilic micro-organisms decompose residual detritus, generating heat from exothermic processes; such heat generation is associated with the well known phenomenon of the elevated temperature of composting.

Consumers

There is an extremely large number of detritus feeders in water. After all, a large quantity of material is carried in by water currents. Even if an organism stays in a fixed position, as long as it has a system for filtering water, it will be able to obtain enough food to get by. Many rooted organisms survive in this way, using developed gills or tentacles to filter the water to take in food, a process known as filter feeding.

Another more widely used method of feeding, which also incorporates filter feeding, is a system where an organism secretes mucus to catch the detritus in lumps, and then carries these to its mouth using an area of cilia. This is called mucus feeding.

Many organisms, including sea slugs and serpent's starfish, scoop up the detritus which has settled on the water bed. Bivalves which live inside the water bed do not simply suck in water through their tubes, but also extend them to fish for detritus on the surface of the bed.

Producers

In contrast, from the point of view of organisms using photosynthesis such as plants and plankton, detritus reduces the transparency of the water and gets in the way of this process. Given that these organisms also require a supply of nutrient salts—in other words fertilizer—for photosynthesis, their relationship with detritus is a complex one.

In land ecosystems, the waste products of plants and animals collect mainly on the ground (or on the surfaces of trees), and as decomposition proceeds, plants are supplied with fertiliser in the form of inorganic salts. In water ecosystems, relatively little waste collects on the water bed, and so the progress of decomposition in water takes a more important role. Investigating the level of inorganic salts in sea ecosystems shows that unless there is an especially large supply, the quantity increases from winter to spring—but is normally extremely low in summer. As such, the quantity of seaweed present reaches a peak in early summer and then decreases. The thinking is that organisms like plants grow quickly in warm periods and thus the quantity of inorganic salts is not enough to keep up with the demand. In other words, during winter, plant-like organisms are inactive and collect fertiliser, but if the temperature rises to some extent they will use this up in a very short period.

It is not entirely true that their productivity falls during the warmest periods. Organisms such as dinoflagellate have mobility, the ability to take in solid food, and the ability to photosynthesise. This type of micro-organism can take in substances such as detritus to grow, without waiting for it to be broken down into fertiliser.

Aquariums

In recent years, the word detritus has also come to be used in relation to aquariums (the word "aquarium" is a general term for any installation for keeping aquatic animals).

When animals such as fish are kept in an aquarium, substances such as excreta, mucus and dead skin cast off during moulting are produced by the animals and, naturally, generate detritus, and are continually broken down by micro-organisms.

Modern sealife aquariums often use the Berlin Method, which employs a piece of equipment called a protein skimmer, which produces air bubbles which the detritus adheres to, and forces it outside the tank before it decomposes, and also a highly porous type of natural rock called live rock where many bentos and bacteria live (hermatype which has been dead for some time is often used), which causes the detritus-feeding bentos and micro-organisms to undergo a detritus cycle. The Monaco system, where an anaerobic layer is created in the tank, to denitrify the organic compounds in the tank, and also the other nitrogen compounds, so that the decomposition process continues until the stage where water, carbon dioxide and nitrogen are produced, has also been implemented.

Initially, the filtration systems in water tanks often worked as the name suggests, using a physical filter to remove foreign substances in the water. Following this, the standard method for maintaining the water quality was to convert ammonium or nitrates in excreta, which have a high degree of neurotoxicity, but the combination of detritus feeders, detritus and micro-organisms has now brought aquarium technology to a still higher level.

See also

Citations

  1. ^ C.M. Hogan, 2008
  2. ^ D.A. Grimaldi, 2005
  3. ^ B.C. Patten, 1975

Sources

  • Bernard C. Patten (1975) Systems Analysis and Simulation in Ecology, Academic Press, 607 pages ISBN 0-12-547203-X
  • C. Michael Hogan (2008) "Western fence lizard (Sceloporus occidentalis)", Globaltwitcher, ed. Nicklas Stromberg [1]
  • David Author Grimaldi and Michael S. Author (2005) Engelevolution of the insects, Cambridge University Press ISBN 0-521-82149-5
  • Some of this article was translated from the equivalent article in the Japanese-language Wikipedia, as it was on September 1, 2006.
Asterix

Asterix or The Adventures of Asterix (French: Astérix or Astérix le Gaulois [asteʁiks lə ɡolwa]) is a series of French comics. The series first appeared in the Franco-Belgian comics magazine Pilote on 29 October 1959. It was written by René Goscinny and illustrated by Albert Uderzo until the death of Goscinny in 1977. Uderzo then took over the writing until 2009, when he sold the rights to publishing company Hachette. In 2013, a new team consisting of Jean-Yves Ferri (script) and Didier Conrad (artwork) took over. As of 2017, 37 volumes have been released, with a 38th forthcoming 2019.

Detritivore

Detritivores, also known as detrivores, detritophages, detritus feeders, or detritus eaters, are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as faeces). There are many kinds of invertebrates, vertebrates and plants that carry out coprophagy. By doing so, all these detritivores contribute to decomposition and the nutrient cycles. They should be distinguished from other decomposers, such as many species of bacteria, fungi and protists, which are unable to ingest discrete lumps of matter, but instead live by absorbing and metabolizing on a molecular scale (saprotrophic nutrition). However, the terms detritivore and decomposer are often used interchangeably.

Detritivores are an important aspect of many ecosystems. They can live on any type of soil with an organic component, including marine ecosystems, where they are termed interchangeably with bottom feeders.

Typical detritivorous animals include millipedes, springtails, woodlice, dung flies, slugs, many terrestrial worms, sea stars, sea cucumbers, fiddler crabs, and some sedentary polychaetes such as worms of the family Terebellidae).

Scavengers are not typically thought to be detritivores, as they generally eat large quantities of organic matter, but both detritivores and scavengers are the same type of cases of consumer-resource systems. The consumption of wood, whether alive or dead, is known as xylophagy. Τhe activity of animals feeding only on dead wood is called sapro-xylophagy and those animals, sapro-xylophagous. It is a good source of manure.

Detritus (geology)

Detritus ( ; adjective detrital ) is particles of rock derived from pre-existing rock through processes of weathering and erosion. A fragment of detritus is called a clast. Detrital particles can consist of lithic fragments (particles of recognisable rock), or of monomineralic fragments (mineral grains). These particles are often transported through sedimentary processes into depositional systems such as riverbeds, lakes or the ocean, forming sedimentary successions. Diagenetic processes can transform these sediments into rock through cementation and lithification, forming sedimentary rocks such as sandstone. These rocks can then in turn again be weathered and eroded to form a second generation of sediment.

Naididae

The Naididae (formerly known as Tubificidae) are a family of clitellate oligochaete worms like the sludge worm, Tubifex tubifex. They are key components of the benthic communities of many freshwater and marine ecosystems. In freshwater aquaria they may be referred to as detritus worms.

Saprotrophic nutrition

Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi (for example Mucor) and soil bacteria. Saprotrophic microscopic fungi are sometimes called saprobes; saprotrophic plants or bacterial flora are called saprophytes (sapro- + -phyte, "rotten material" + "plant"), though it is now believed that all plants previously thought to be saprotrophic are in fact parasites of microscopic fungi or other plants. The process is most often facilitated through the active transport of such materials through endocytosis within the internal mycelium and its constituent hyphae.Various word roots relating to decayed matter (detritus, sapro-), eating and nutrition (-vore, -phage), and plants or life forms (-phyte, -obe) produce various terms, such as detritivore, detritophage, saprotroph, saprophyte, saprophage, and saprobe; their meanings overlap, although technical distinctions (based on physiologic mechanisms) narrow the senses. For example, usage distinctions can be made based on macroscopic swallowing of detritus (as an earthworm does) versus microscopic lysis of detritus (as a mushroom does).

A facultative saprophyte appears on stressed or dying plants and may combine with the live pathogens..

Sedimentary rock

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particles and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus (organic matter). Before being deposited, the geological detritus was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts (mainly shells) of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies (marine snow). Sedimentation may also occur as dissolved minerals precipitate from water solution.

The sedimentary rock cover of the continents of the Earth's crust is extensive (73% of the Earth's current land surface), but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding. The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering, for example in the construction of roads, houses, tunnels, canals or other structures. Sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores.

The study of the sequence of sedimentary rock strata is the main source for an understanding of the Earth's history, including palaeogeography, paleoclimatology and the history of life. The scientific discipline that studies the properties and origin of sedimentary rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry and structural geology. Sedimentary rocks have also been found on Mars.

Troll (Discworld)

Trolls in Terry Pratchett's Discworld novels, unlike the monstrous trolls of folklore and J. R. R. Tolkien, have been subverted into a moderately civilised race. Trolls on the Discworld are, essentially, living, mobile rocks. Trolls have grown to overcome those vicious stereotypes of yore and have lived very prosperous lives in heavily populated cities with (relatively) little killing, and they have held jobs as diverse as police officer and concert promoter. They have also held jobs as "bridgekeepers", collecting tolls from those that cross their bridges. It is relatively harmless, although farmers in the company of billy goats have to pay a hefty toll.

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