Trophic mutualism is a key type of ecological mutualism. Specifically, "trophic mutualism" refers to the transfer of energy and nutrients between two

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. This is also sometimes known as resource-to-resource mutualism. Trophic mutualism often occurs between an

autotroph An autotroph is an organism that can convert Abiotic component, abiotic sources of energy into energy stored in organic compounds, which can be used by Heterotroph, other organisms. Autotrophs produce complex organic compounds (such as carbohy ...

and a

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

. Although there are many examples of trophic mutualisms, the heterotroph is generally a fungus or bacteria. This mutualism can be both

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism ...

and opportunistic.

Examples

*Rhizobia –

Rhizobia Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. I ...

are bacteria that conduct

nitrogen fixation Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

for legume plants. Specifically, these bacteria can be from genera ''Allorhizobium, Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium, or Sinorhizobium''.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. In this mutualistic relationship, the bacteria grow on or within the root hair and penetrate into the plant tissuesTownsend, C.R., M. Begon, and J.L. Harper, Essentials Of Ecology Third Edition 2008, Malden, MA: Backwell Publishing 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 Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

and

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

. The role that rhizobia play in fixing nitrogen for legumes is the basis for why legumes can be used in

crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. This practice reduces the reliance of crops on one set of nutrients, pest and weed pressure, along with the pro ...

. *Mycorrhizae –

Mycorrhizae A mycorrhiza (; , mycorrhiza, or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, the plant root system and its surroundings. Mycorrhizae play ...

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 In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term ...

. Three main types of mycorrhizae exist: :# Arbuscula: found in non-woody and tropical plants :# Ectomycorrhiza: found in boreal and temperate forests :# Ericoid: found in species of the heathland. *Digestive symbiotes – Digestive symbiotes are an example of an important trophic mutualism that does not occur between an autotroph and heterotroph. Bacteria known as "extracellular symbionts" live within the gastrointestinal tracts of

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

, 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.

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. 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. 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 Leafcutter ants are fungus-growing ants that share the behaviour of cutting leaves which they carry back to their nests to farm fungus. Next to humans, leafcutter ants form some of the largest and most complex animal societies on Earth. In a few ...

that engage in trophic mutualism with a fungus.Weber, Neal A. 1972. Gardening Ants the Attines. The American Philosophical Society. Philadelphia 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.

References

{{modelling ecosystems Ecology terminology Behavioral ecology Mutualism (biology)

Examples

History of research

See also

References