Trophic mutualism

Trophic mutualism is a key type of ecological mutualism. Specifically, "trophic mutualism" refers to the transfer of energy and nutrients between two species. This is also sometimes known as resource-to-resource mutualism. Trophic mutualism often occurs between an autotroph and a heterotroph.[1] Although there are many examples of trophic mutualisms, the heterotroph is generally a fungus or bacteria. This mutualism can be both obligate and opportunistic.

Examples

  • RhizobiaRhizobia are bacteria that conduct nitrogen fixation for legume plants. Specifically, these bacteria can be from generas Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium, or Sinorhizobium.[2] In this mutualistic relationship, the bacteria grow on or within the root hair and penetrate into the plant tissues[3] Although the exact means of interaction between the Rhizobia and plant varies with genus and species, all forms of this interaction are made up of the infection of bacteria, bacteria colonization, control of O2, and exchange of carbon and nitrogen.[2] The role that rhizobia play in fixing nitrogen for legumes is the basis for why legumes can be used in crop rotation.[4]
  • MycorrhizaeMycorrhizae are similar to rhizobia in that they interact with plants at their roots. Whereas rhizobia are bacteria that fix nitrogen, mycorrhizae are fungi that bring nutrients to the plants in return for carbon. Mycorrhizas are also capable of improving water uptake and communicating to their hosts to resist to pathogens.[5] Three main types of mycorrhizae exist:
  1. Arbuscula: found in non-woody and tropical plants
  2. Ectomycorrhiza: found in boreal and temperate forests
  3. Ericoid: found in species of the heathland.[3]
  • Digestive symbiotes – Digestive symbyotes are an example of an important trophic mutualism that does not occur between an autotroph and heterotroph. Bacteria known as "extracellular symbionts"[3] live within the gastrointestinal tracts of vertebrates, where they aid in the digestion of food. The bacteria benefits by extracting substrates from the eaten food, while the animal’s assimilation is increased by being able to digest certain foods that its natural system cannot. (book) In addition, these bacteria create short-chain fatty acids (SCFA), providing the vertebrate with energy totaling up to anywhere from 29%-79% of the vertebrate’s maintenance energy depending on the species.[6]

History of research

Ecologists first began to understand trophic mutualisms in the mid-20th century with the investigation of nutrient abundance and distribution. One of the first trophic mutualisms was discovered in 1958 by Professor Leonard Muscatine of UCLA, the relationship between endozoic algae and coral.[7] In this relationship, the algae provides the coral with a Carbon source to develop its CaCO3 skeleton and the coral secretes a protecting nutrient-rich mucus which benefits the algae. Perhaps one of the most famous discoveries made by Muscatine in the field of trophic mutualism came about 10 years later in another aquatic based system-the relationship between algae and water hydra.[8] This work was significant in establishing the presence of mutualistic relationships in both aquatic and terrestrial environments.

Perhaps the most widely acclaimed example of a trophic mutualism was the discovery of the leafcutter ant that engage in trophic mutualism with a fungus.[9] These ants cultivate a certain type of fungus by providing it with leaves and other nutrients. In turn, the ants will feed on a special nutrient that is only created by the fungus they nurture. This trophic mutualism was studied in detail in the 1970s and since.

See also

References

  1. ^ Odum, Eugene. Fundamentals of Ecology. 3rd ed. Philadelphia: W.B. Saunders Company, 1971.
  2. ^ a b Vessey, K.J., K. Pawlowski, and B. Bergman, Root-based N2-fixing symbioses: Legumes, actinorhizal plants, Parasponiasp. and cycads. Plant and Soil 2005. 266(1-2): p. 205-230.
  3. ^ a b c Townsend, C.R., M. Begon, and J.L. Harper, Essentials Of Ecology Third Edition 2008, Malden, MA: Backwell Publishing
  4. ^ Saito, K., B. Linquist, and B. Keobualapha, Stylosanthes guianensis as a short-term fallow crop for improving upland rice productivity in northern Laos. Field Crops Research 2006. 96(2/3): p. 438-447.
  5. ^ Douglas H. Boucher, Sam James and Kathleen H. Keeler Annual Review of Ecology and Systematics, Vol. 13, (1982), pp. 315–347
  6. ^ Stevens, C.E. and I.D. Hume, Contributions of Microbes in Vertebrate Gastrointestinal Tract to Production and Conservation of Nutrients. Physiological Reviews, 1998. 72(2): p. 383-427.
  7. ^ Hoegh-Guldberg, O., et al., Len Muscatine (1932–2007) and his contributions to the understanding of algal-invertebrate endosymbiosis. Coral Reefs, 2007. 26(4): pp. 731–739.
  8. ^ Muscatine, Leonard, and Howard Lenhoff. "Symbiosis: On the Role of Algae Symbiotic with Hydra." Science 142 (19681): 956-58.e
  9. ^ Weber, Neal A. 1972. Gardening Ants the Attines. The American Philosophical Society. Philadelphia
Cascade effect (ecology)

An ecological cascade effect is a series of secondary extinctions that is triggered by the primary extinction of a key species in an ecosystem. Secondary extinctions are likely to occur when the threatened species are: dependent on a few specific food sources, mutualistic (dependent on the key species in some way), or forced to coexist with an invasive species that is introduced to the ecosystem. Species introductions to a foreign ecosystem can often devastate entire communities, and even entire ecosystems. These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely. Olsen et al. showed that exotic species have caused lake and estuary ecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds. However, the principal cause of cascade effects is the loss of top predators as the key species. As a result of this loss, a dramatic increase (ecological release) of prey species occurs. The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction. When the prey's food resources disappear, they starve and may go extinct as well. If the prey species is herbivorous, then their initial release and exploitation of the plants may result in a loss of plant biodiversity in the area. If other organisms in the ecosystem also depend upon these plants as food resources, then these species may go extinct as well. An example of the cascade effect caused by the loss of a top predator is apparent in tropical forests. When hunters cause local extinctions of top predators, the predators' prey's population numbers increase, causing an overexploitation of a food resource and a cascade effect of species loss. Recent studies have been performed on approaches to mitigate extinction cascades in food-web networks.

Energy flow (ecology)

In ecology, energy flow, also called the calorific flow, refers to the flow of energy through a food chain, and is the focus of study in ecological energetics. In an ecosystem, ecologists seek to quantify the relative importance of different component species and feeding relationships.

A general energy flow scenario follows:

Solar energy is fixed by the photoautotrophs, called primary producers, like green plants. Primary consumers absorb most of the stored energy in the plant through digestion, and transform it into the form of energy they need, such as adenosine triphosphate (ATP), through respiration. A part of the energy received by primary consumers, herbivores, is converted to body heat (an effect of respiration), which is radiated away and lost from the system. The loss of energy through body heat is far greater in warm-blooded animals, which must eat much more frequently than those that are cold-blooded. Energy loss also occurs in the expulsion of undigested food (egesta) by excretion or regurgitation.

Secondary consumers, carnivores, then consume the primary consumers, although omnivores also consume primary producers. Energy that had been used by the primary consumers for growth and storage is thus absorbed into the secondary consumers through the process of digestion. As with primary consumers, secondary consumers convert this energy into a more suitable form (ATP) during respiration. Again, some energy is lost from the system, since energy which the primary consumers had used for respiration and regulation of body temperature cannot be utilized by the secondary consumers.

Tertiary consumers, which may or may not be apex predators, then consume the secondary consumers, with some energy passed on and some lost, as with the lower levels of the food chain.

A final link in the food chain are decomposers which break down the organic matter of the tertiary consumers (or whichever consumer is at the top of the chain) and release nutrients into the soil. They also break down plants, herbivores and carnivores that were not eaten by organisms higher on the food chain, as well as the undigested food that is excreted by herbivores and carnivores. Saprotrophic bacteria and fungi are decomposers, and play a pivotal role in the nitrogen and carbon cycles.The energy is passed on from trophic level to trophic level and each time about 90% of the energy is lost, with some being lost as heat into the environment (an effect of respiration) and some being lost as incompletely digested food (egesta). Therefore, primary consumers get about 10% of the energy produced by autotrophs, while secondary consumers get 1% and tertiary consumers get 0.1%. This means the top consumer of a food chain receives the least energy, as a lot of the food chain's energy has been lost between trophic levels. This loss of energy at each level limits typical food chains to only four to six links.

Food web

A food web (or food cycle) is the natural interconnection of food chains and a graphical representation (usually an image) of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs. To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic matter from inorganic substances, including both minerals and gases such as carbon dioxide. These chemical reactions require energy, which mainly comes from the Sun and largely by photosynthesis, although a very small amount comes from hydrothermal vents and hot springs. A gradient exists between trophic levels running from complete autotrophs that obtain their sole source of carbon from the atmosphere, to mixotrophs (such as carnivorous plants) that are autotrophic organisms that partially obtain organic matter from sources other than the atmosphere, and complete heterotrophs that must feed to obtain organic matter. The linkages in a food web illustrate the feeding pathways, such as where heterotrophs obtain organic matter by feeding on autotrophs and other heterotrophs. The food web is a simplified illustration of the various methods of feeding that links an ecosystem into a unified system of exchange. There are different kinds of feeding relations that can be roughly divided into herbivory, carnivory, scavenging and parasitism. Some of the organic matter eaten by heterotrophs, such as sugars, provides energy. Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes - from cyanobacteria to giant redwoods, and from viruses and bdellovibrio to blue whales.

Charles Elton pioneered the concept of food cycles, food chains, and food size in his classical 1927 book "Animal Ecology"; Elton's 'food cycle' was replaced by 'food web' in a subsequent ecological text. Elton organized species into functional groups, which was the basis for Raymond Lindeman's classic and landmark paper in 1942 on trophic dynamics. Lindeman emphasized the important role of decomposer organisms in a trophic system of classification. The notion of a food web has a historical foothold in the writings of Charles Darwin and his terminology, including an "entangled bank", "web of life", "web of complex relations", and in reference to the decomposition actions of earthworms he talked about "the continued movement of the particles of earth". Even earlier, in 1768 John Bruckner described nature as "one continued web of life".

Food webs are limited representations of real ecosystems as they necessarily aggregate many species into trophic species, which are functional groups of species that have the same predators and prey in a food web. Ecologists use these simplifications in quantitative (or mathematical representation) models of trophic or consumer-resource systems dynamics. Using these models they can measure and test for generalized patterns in the structure of real food web networks. Ecologists have identified non-random properties in the topographic structure of food webs. Published examples that are used in meta analysis are of variable quality with omissions. However, the number of empirical studies on community webs is on the rise and the mathematical treatment of food webs using network theory had identified patterns that are common to all. Scaling laws, for example, predict a relationship between the topology of food web predator-prey linkages and levels of species richness.

Invasive species

An invasive species is a species that is not native to a specific location (an introduced species), and that has a tendency to spread to a degree believed to cause damage to the environment, human economy or human health.The term as most often used applies to introduced species that adversely affect the habitats and bioregions they invade economically, environmentally, or ecologically. Such species may be either plants or animals and may disrupt by dominating a region, wilderness areas, particular habitats, or wildland–urban interface land from loss of natural controls (such as predators or herbivores). This includes plant species labeled as exotic pest plants and invasive exotics growing in native plant communities. The European Union defines "Invasive Alien Species" as those that are, firstly, outside their natural distribution area, and secondly, threaten biological diversity. The term is also used by land managers, botanists, researchers, horticulturalists, conservationists, and the public for noxious weeds.The term "invasive" is often poorly defined or very subjective and some broaden the term to include indigenous or "native" species, that have colonized natural areas - for example deer considered by some to be overpopulating their native zones and adjacent suburban gardens in the Northeastern and Pacific Coast regions of the United States.The definition of "native" is also sometimes controversial. For example, the ancestors of Equus ferus (modern horses) evolved in North America and radiated to Eurasia before becoming locally extinct. Upon returning to North America in 1493 during their hominid-assisted migration, it is debatable as to whether they were native or exotic to the continent of their evolutionary ancestors.Notable examples of invasive plant species include The kudzu vine, Andean pampas grass, and yellow starthistle. Animal examples include the New Zealand mud snail, feral pigs, European rabbits, grey squirrels, domestic cats, carp and ferrets.Invasion of long-established ecosystems by organisms from distant bio-regions is a natural phenomenon, but has been accelerated massively by humans, from their earliest migrations though to the age of discovery, and now international trade.

Mesopredator release hypothesis

The mesopredator release hypothesis is an ecological theory used to describe the interrelated population dynamics between apex predators and mesopredators within an ecosystem, such that a collapsing population of the former results in dramatically-increased populations of the latter. This hypothesis describes the phenomenon of trophic cascade in specific terrestrial communities.

A mesopredator is a medium-sized, middle trophic level predator, which both preys and is preyed upon. Examples are raccoons, skunks, snakes, cownose rays, and small sharks.

Productivity (ecology)

In ecology, productivity refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface (or volume) per unit time, for instance grams per square metre per day (g m−2 d−1). The mass unit may relate to dry matter or to the mass of carbon generated. Productivity of autotrophs such as plants is called primary productivity, while that of heterotrophs such as animals is called secondary productivity.

Spotted jelly

The spotted jelly (Mastigias papua), lagoon jelly, golden medusa, or Papuan jellyfish, is a species of jellyfish from the Indo-Pacific oceans. Like corals, sea anemones, and other sea jellies, it belongs to the phylum Cnidaria. Mastigias papua is one of the numerous marine animals living in symbiosis with zooxanthellae, a photosynthetic alga.They have a lifespan of approximately 4 months and are active primarily in mid-summer to early autumn.

Sustainable gardening

Sustainable gardening includes the more specific sustainable landscapes, sustainable landscape design, sustainable landscaping, sustainable landscape architecture, resulting in sustainable sites. It comprises a disparate group of horticultural interests that can share the aims and objectives associated with the international post-1980s sustainable development and sustainability programs developed to address the fact that humans are now using natural biophysical resources faster than they can be replenished by nature.Included within this compass are those home gardeners, and members of the landscape and nursery industries, and municipal authorities, that integrate environmental, social, and economic factors to create a more sustainable future.

Organic gardening and the use of native plants are integral to sustainable gardening.

Trophic

Trophic, from Ancient Greek τροφικός (trophikos) "pertaining to food or nourishment", may refer to:

Trophic cascade

Trophic coherence

Trophic dynamics

Trophic egg

Trophic factor receptor

Trophic factor

Trophic function

Trophic hormone

Trophic level index

Trophic level

Trophic mutualism

Trophic network

Trophic pyramid

Trophic species

Trophic state index

Trophic ulcer

Trophic web

General
Producers
Consumers
Decomposers
Microorganisms
Food webs
Example webs
Processes
Defense,
counter
Ecology: Modelling ecosystems: Other components
Population
ecology
Species
Species
interaction
Spatial
ecology
Niche
Other
networks
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