Commensalism

8 Key excerpts on "Commensalism"

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  Ecology

  From Individuals to Ecosystems

  • Michael Begon, Colin R. Townsend, John L. Harper(Authors)
  • 2009(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  13.1 Introduction: symbionts, mutualists, commensals and engineers No species lives in isolation, but often the association with another species is especially close: for many organisms, the habitat they occupy is an individual of another species. Parasites live within the body cavities or even the cells of their hosts; nitrogen-fixing bacteria live in nodules on the roots of leguminous plants; and so on. Symbiosis (‘living together’) is the term that has been coined for such close physical associations between species, in which a ‘symbiont’ occupies a habitat provided by a ‘host’. In fact, parasites are usually excluded from the category of sym- bionts, which is reserved instead for interactions where there is at least the suggestion of ‘mutualism’. A mutualistic relationship is simply one in which organisms of different species interact to their mutual benefit. It usually involves the direct exchange of goods or services (e.g. food, defense or transport) and typically results in the acquisition of novel capabilities by at least one part- ner (Herre et al., 1999). Mutualism, therefore, need not involve close physical association: mutualists need not be symbionts. For example, many plants gain dispersal of their seeds by offering a reward to birds or mammals in the form of edible fleshy fruits, and many plants assure effective pollination by offering a resource of nectar in their flowers to visiting insects. These are mutualistic interactions but they are not symbioses. It would be wrong, however, to see mutualistic interactions simply as conflict-free relationships from which nothing but good things flow for both partners. Rather, current evolutionary thinking views mutualisms as cases of reciprocal exploitation where, none the less, each partner is a net beneficiary (Herre & West, 1997).

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  Microbial Symbioses

  • Sebastien Duperron(Author)
  • 2016(Publication Date)
  • ISTE Press - Elsevier

    (Publisher)

  Figure 1.1 ). In French, the word “symbiosis” retains this connotation and is still often used (and taught) as a synonym of mutualism, even of obligate mutualism. The Larousse Dictionary, for example, defines it as the constant, obligatory and specific association between two organisms that cannot live without one another, each of them benefiting from the association. The Cambridge Dictionary defines symbiosis as a relationship between two types of animals or plants in which each provides the other with the conditions necessary for its continued existence. The English meaning is broader and incorporates forms of interaction that do not necessarily benefit each partner, such as Commensalism, in which the association is beneficial for one and neutral for the other, and parasitism, in which the benefit for one is obtained to the detriment of the other, and even mutually negative relationships. How, therefore, do we define the concept? This is not a new problem: in 1897, for example, the lichens specialist Albert Schneider suggested that the definition should be limited to associations that lead to the loss or gain of nutrients, and alternative definition attempts have been proposed in a number of publications since.

  The concept of benefit is central to the debate. This concept is related to the measurement of the success of each partner and to the idea that the association increases this success. The success of an individual can be measured by the number of offspring that reach reproductive age. This is called fitness or reproductive success. It is often very difficult to measure. The benefit of strictly obligate symbiosis, for example, is obvious, because survival falls to zero when there is no association. But at this point, the entity formed by the partners is so interdependent that discussing the benefit to one of them in particular does not make much sense, since there is no point of comparison. Practical challenges are encountered even with facultative symbiosis. For bacterial symbionts, the difficulty of identifying, quantifying and monitoring the growth of bacteria in their natural environment renders illusory any measurement of the fitness of free-living forms, and therefore any comparison with that of symbiotic forms. Finally, the concept of benefit is offset by the cost of symbiosis: resources transmitted to the partner rather than used for oneself, for example. For similar reasons, it is extremely difficult and often even impossible to measure this cost. Besides, it should be noted that the effects of a single interaction on the partners may be beneficial or negative, depending on environmental conditions or at different times of their life cycle. These difficulties mean that symbiosis cannot be defined simply as a mutualist relationship. Indeed, in many cases, we cannot even answer the simple question: “Is this association a symbiosis?”. Anton de Bary’s original definition initially appears more usable, because it is less restrictive. However, attempting to include every type of inter-species relationship in the definition results in every association between organisms being considered symbiosis, even those that are temporary and short-lived, meaning that we lose sight of what distinguishes this particular type of association.

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  Ecology

  From Individuals to Ecosystems

  • Michael Begon, Colin R. Townsend(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  2008 ).

  It would be mistaken to think of mutualism and Commensalism as less common or ecologically less important than competition, predation or parasitism (Bruno et al., 2003 ). Some animals and many plants provide habitat for their commensal partners. And almost all the plants that dominate grasslands, heaths and forests have roots that have an intimate mutualistic association with fungi, most corals depend on the unicellular algae within their cells, many flowering plants need their insect pollinators, and many animals carry communities of microorganisms within their guts that they require for effective digestion. In the next section we consider Commensalisms in more detail. Then we deal with examples of mutualism before finally considering mathematical models of Commensalism and mutualism.

  13.2 Commensalisms

  'habitat' Commensalisms: ecosystem engineers provide habitat for other species

  There are many ‘interactions’ between two species in which the first provides a habitat for the second, but there is no real suspicion that the first either benefits or suffers in any measurable way as a consequence. Trees, for example, provide habitats for the many species of birds, bats and climbing and scrambling animals that are absent from treeless environments. Lichens and mosses develop on tree trunks, and climbing plants such as ivy, vines and figs, though they root in the ground, use tree trunks as support to extend their foliage up into a forest canopy. Trees are therefore good examples of what have been called ecological or ecosystem ‘engineers’ (Jones et al., 1994 ). By their very presence, they create, modify or maintain habitats for others (see also Section 16.4 ). In marine communities, the solid surfaces of larger organisms are just as important contributors to biodiversity. Kelps and other seaweeds normally grow only where they can be anchored on rocks, but their fronds are colonised in turn by filamentous algae, tube‐forming worms (Spirorbis) and modular animals such as hydroids and bryozoans that depend on seaweeds for anchorage and access to resources in the moving waters of the sea. Turning to freshwater habitats, many crayfish species build burrows as refuges that are particularly important in seasonal environments that may dry up. Gramastacus insolitus, a threatened species endemic to shallow swamps and stream margins in southern Australia, is a very small crayfish (<4 cm total length) that does not build burrows. It only occurs as a commensal associated with larger species (G. falcata and Cherax destructor) that build deep burrows connected to the ground water, the smaller species using cracks and depressions in the burrows as aestivation sites in dry seasons. G. insolitus is part of an assemblage of animals that take advantage of this ‘engineered' habitat (Johnston & Robson, 2009

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  The Theory of Endobiogeny

  Volume 2: Foundational Concepts for Treatment of Common Clinical Conditions

  • Kamyar M. Hedayat, Jean-Claude Lapraz(Authors)
  • 2019(Publication Date)
  • Academic Press

    (Publisher)

  Golestan , translated by George M. Hedayat, MD and Kamyar M. Hedayat, MD.

  The essence of Life, as an active and expressed principle, is interconnectedness. No organism can live unto itself. It must live with or on all other forms in life. It takes and gives back material and energy in death. The symbiosis that is expressed in Life is fractal and occurs at multiple iterations in a scaled hierarchy of interdependence and mutual benefit. If we consider the earth to be a complex, adaptive system like a living organism,2 then all the organisms on the earth are its symbiotes. Each multicellular organism within a species lives by symbiosis with other organisms. Within each multicellular organism live several species in symbiosis with each other. Within a unicellular microbe may live viruses that contribute to the overall fitness of the microbiome by the sharing of genetic material.

  Commensal organisms benefit one another and share the same nutrients. A saprophyte is an organism that feeds off dead or decaying material. Commensalism literally means the act of “sharing a table.” Commensal saprophytic flora within the human being are an endogenous, nonindigenous, semiindependent metabolic organ. From the perspective of the flora, it could be said that the human being is a mobile feeding station, not so different from our ride on the earth as it makes its rotations and revolutions around the sun. Commensal organisms play a role in the structure, function, and metabolism of the human. They aid in the formation and calibration of the adaptive immune system, based on the principle of tolerance, and beyond that, mutual benefit. They aid in metabolism by increasing reclamation of extracted exogenous nutrients and the formation of de novo nutrients.

  Dysbiosis, the imbalance of the quantity, species, location, and/or function of commensal flora is a product of the terrain and the organism’s interaction with its external and internal environments. A host of inflammatory disorders is related to dysbiosis. Disorders as far ranging as autism to asthma and atherosclerosis to obesity have been linked to it. According to the theory of endobiogeny, dysbiosis is not the cause of disease. It is the result of a deranged terrain. Dysbiosis is a mechanism that exacerbates the risk of, or, accelerates the current state of precritical or liminal (viz., critical) disease. Elucidating the relationship of commensal symbiotes to the terrain is capital for the optimal functioning of the metaorganism referred to as the patient.

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  Biology Today and Tomorrow without Physiology

  • Cecie Starr, Christine Evers, Lisa Starr, , Cecie Starr, Christine Evers, Lisa Starr(Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 332 UNIT 4 ECOLOGY 17.3 Direct Species Interactions REMEMBER: Species interactions influence population size (Section 16.3) and can result in directional selection (12.3) and coevolution (12.7). There are five types of direct interactions among species in a community: commen-salism, mutualism, competition, predation, and parasitism (Table 17.1). Three of these—parasitism, Commensalism, and mutualism—can be a symbiosis . Symbiosis means “living together.” Symbiotic species, also known as symbionts, spend most or all of their life cycle in close association with each other. An endosymbiont is a spe-cies that lives inside its partner species. Regardless of whether one species helps or hurts another, two species that inter-act closely may coevolve over generations. Recall that with coevolution, each species is a selective agent that shifts the range of variation in the other. Commensalism and Mutualism Commensalism benefits one species and does not affect the other. For example, some orchids that live attached to a tree trunk or branch (Figure 17.3) benefit by having a perch in the sun, while the tree that provides this support is unaffected. As another example, commensal bacteria live in the gut of many animals. They benefit by having a warm, nutrient-rich place to live, and their presence neither helps nor harms their host. Other gut bacteria assist their host by aiding in digestion or synthesizing vitamins. An interaction that benefits both species is a mutualism . Flowering plants and their pollinators are a familiar example. In some cases, coevolution of two spe-cies results in a mutual dependence.

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  Introduction to Population Ecology

  • Larry L. Rockwood(Author)
  • 2015(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  +/− = A biological association in which one individual benefits while the other is harmed. Such interactions include predator/prey, herbivore/plant, and parasite/host relationships. +/0 = Commensalism. One partner benefits from the interaction, while the other experiences no particular benefit or harm. Examples include: (i) seeds with barbs that stick to the fur of animals and are thereby dispersed; (ii) ectoparasites (mites, bacteria etc.) that live on the skin of animals but do no harm to the host; (iii) a bird nest in a tree; or (iv) a cattle egret which feeds more efficiently in the company of a cow. +/+ = Mutualism. Both partners benefit from the interaction. Examples include: (i) “cleaners” and their hosts such as ox-peckers and ungulates, or cleaner shrimp and fish; (ii) pollinator-plant interactions; (iii) frugivore-plant relationships; (iv) a variety of ant-plant interactions; and (v) relationships between higher plants and fungi (mycorrhizae) or bacterial (Rhizobium) nitrogen fixers. Introduction to Population Ecology, Second Edition. Larry L. Rockwood. © 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/rockwood/populationecology 173 174 Part 2 We do not usually consider the above associations to be "symbiotic" unless there is a definite "living together" of the associates. Thus the algae and fungi that make up lichens are symbiotic, as are Rhizobium bacteria that live in the roots of legumes. But plant-pollinator and bird-seed dispersal interactions are not symbiotic. Predator–prey, parasite–host, and plant–herbivore interactions These interactions are of such fundamental importance in that they have effects at the population, the community and the ecosystem level. 1. At the population level, predation, herbivory and parasitism often control or help regulate animal and plant populations.

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  Biochemical Engineering

  • Douglas S. Clark, Harvey W. Blanch(Authors)
  • 1997(Publication Date)
  • CRC Press

    (Publisher)

  Interactions can be classified by whether an organism is benefited, harmed, or not affected by the presence of another organism. Table 7.1 lists the common types of interaction. Neutralism connotes a lack of interaction between species, so that the growth char- acteristics of one species are unaffected by the presence of another. This implies that the species must have different growth limiting substrates and that their by-products do not influence other species. As one might expect, this is not frequently observed and few instances of pure neutralism have been reported in experimental systems. 578 Microbial Interactions 579 Table 7.1. Microbial interactions and their definitions. Interaction Definition Effect of Interaction Population A Population B Neutralism Lack of interaction 0 0 Commensalism One member benefits while the other is unaffected 0 + Mutualism Each member benefits from the other + + Competition A "race" for nutrients or space - - Amensalism One species adversely changes the environment for the other 0 or + - Parasitism One organism steals from the other + - Predation One organism ingests the other + - 0: unaffected; +: benefited; impaired In Commensalism, one organism requires a product from the other to grow, while not affecting the other organism to an appreciable extent. Another type of commensal interaction occurs when one organism removes a toxic product from the environment, enabling the second species to grow. The second species provides no benefit to the first, distinguishing this interaction from mutualism. An example of the first type of commensal interaction is that of Proteus vulgaris and Saccharomyces cerevisiae. The yeast produces niacin, which is required for the growth of the Proteus species. If niacin is supplied to a mixed culture of both species, the dependence vanishes. Table 7.2 lists some common types of commensal interactions that have been observed.

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  The Ecological World View

  • Charles Krebs(Author)
  • 2008(Publication Date)
  • CSIRO PUBLISHING

    (Publisher)

  Commensalisms .

  Many mutualisms have been known for hundreds of years. Bees pollinate flowers and gain by obtaining pollen as food, while the plants gain by gene flow (through movement of pollen) and seed fertilization. Nitrogen-fixing bacteria and mycorrhizal fungi inhabit the roots of plants and gain protection and carbohydrates from the plant while supplying nitrogen or other soil nutrients to the plant in exchange. But we should always remember that there are costs to mutualisms as well as benefits, and we need to determine how the benefits exceed the costs for positive interactions. Ecologists first wish to describe these mutualisms and then ask how they might affect the distribution and abundance of species in nature (Essay 9.1).

  9.2 MUTUALISTIC INTERACTIONS OCCUR WHEN ANIMALS POLLINATE AND DEFEND PLANTS

  While it is tempting to think of mutualisms in their simplest form as a two-species interaction—for example, between a particular pollinator and a particular plant species—in natural ecosystems specialized, two-species partnerships are rare. We must remember to think instead of multi-species systems in which, for example, many insects pollinate a particular plant, and a single pollinator may use pollen from several different plant species. For simplicity, most natural history studies concentrate on two-species interactions, from which we can gradually build a more complex picture. Let us consider two examples of mutualisms.

  ESSAY 9.1 WHY ARE CORALS BLEACHING?

  Coral reef bleaching has increased dramatically in many tropical areas around the globe in the last 20 years. Corals are animals that contain symbiotic algae within their cells, and this symbiotic relationship is one of the most important mutualisms in the biosphere. The symbiotic algae provide color to the corals and undertake photosynthesis, thus contributing to coral growth—a positive relationship. When corals bleach they lose their symbiotic algae, and therefore their color, and often die. Widespread bleaching can cause the death of whole coral reefs. The primary cause of coral bleaching is thought to be elevated sea surface temperatures. Many reef-building corals live very close to their upper lethal temperatures, and small increases of 0.5 to 1.5°C over a few weeks, or larger increases of 3–4°C over several days, can kill corals (Huppert and Stone 1998

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