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Symbiosis is the concept of a mutually beneficial relationship between two different species, where both organisms benefit from the association. It defines different types of symbiotic relationships, such as mutualism, commensalism, and parasitism, and provides examples of each. It also describes the evolution of symbiosis, including how symbiotic relationships can evolve over time and how they can lead to coevolution. Additionally, the ecological importance of symbiosis and its role in the functioning of ecosystems, as well as its potential applications in fields such as agriculture and medicine.

Definition[edit]
Diagram of the six possible types of symbiotic relationship, from mutual benefit to mutual harm. The definition of symbiosis was a matter of debate for 130 years. In 1877, Albert Bernhard Frank used the term symbiosis to describe the mutualistic relationship in lichens. In 1878, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms". The definition has varied among scientists, with some advocating that it should only refer to persistent mutualisms, while others thought it should apply to all persistent biological interactions (in other words, to mutualism, commensalism, and parasitism, but excluding brief interactions such as predation). In the 21st century, the latter has become the definition widely accepted by biologists.

In 1949, Edward Haskell proposed an integrative approach with a classification of "co-actions", later adopted by biologists as "interactions".

Obligate versus facultative[edit]
Relationships can be obligate, meaning that one or both of the symbionts entirely depend on each other for survival. For example, in lichens, which consist of fungal and photosynthetic symbionts, the fungal partners cannot live on their own. The algal or cyanobacterial symbionts in lichens, such as Trentepohlia, can generally live independently, and their part of the relationship is therefore described as facultative (optional), or non-obligate.

Competition[edit]
Competition is the interaction of two individuals or species when the presence of one reduces the fitness of the other. This relationship is typically made easier by a restricted quantity of at least one resource (such as food, water, and territory) shared by both. Begon, M.; Harper, J. L.; Townsend, C. R. (1996)   They're different forms of competition in animals. The three forms of competition in animals are interference competition, exploitation competition, and apparent competition. When one animal prevents another from physically establishing itself in a particular area of the ecosystem or interferes with their feeding, survival, or reproduction, interference competition immediately arises between individuals. Competitions interference competitions can be aggressive or passive. For instance, competition happens when one organism aggressively stops another from obtaining a scarce resource.

This is called passive competition, when an organism prohibits another from receiving help without engaging in hostile behavior, such as by secreting compounds that drive away rivals. Due to the struggle for scarce resources, this type of competition is also known as contest competition. As an illustration, when hyenas approach the dead animals that the lions consume, the lions become hostile.

The following types of competition are exploitative competitions. When creatures compete for the same resources, such as food or territory, they engage in exploitative competition. This rivalry can also cause other competing organisms to suffer from resource scarcity, affecting their survival and development. It can also happen when a creature takes up too much room in the ecosystem, denying others the ability to thrive. An example of exploitative competition is when a lion pack overeats the herbivore population in a Savanna region, making prey scarce for another predator. Apparent competition is the final type of competition. Apparent competition occurs when two unrelated animals indirectly compete for resources and interact because they prey on the same predator. A hawk that preys on squirrels and mice is an example of apparent competition. (Species Interactions and Competition 2013)

Mutualism[edit]
In a mutualistic symbiosis, both species gain from their contact. Any interaction between two species mutually advantageous to both organisms is a mutually symbiotic relationship. Mutually beneficial partnerships can go so far as to require the other organism for survival. The creatures in mutualistic partnerships receive various advantages, including protection and sustenance. Long-term relationships between members of other species that are mutually beneficial are known as mutualism or interspecies reciprocal altruism. Mutualistic relationships might be required for both species, required for one species but optional for the other, or optional for both. Obligate mutualism is when two or more species interact necessarily for both of them to survive, making them compelled to depend on one another. Obligatory mutualism typically has greater advantages than facultative mutualism. The most significant instance of obligatory mutualism, which involves a partnership between algae and a fungus, is seen in lichens. Facultative mutualism is a relationship between two or more species in which one species gains from the other's presence but can also exist on its own.

In comparison to compulsory mutualism, facultative mutualism offers fewer advantages. Since facultative mutualism is less rigid than obligate mutualism, it can occur between different species. Both species give the other species a resource in a resource-resource mutualism. One species offers a service while the other offers a resource in a service-resource mutualistic relationship. Both species offer assistance to the other species in a service-service mutualism. Honeybees and flowering plants have a mutualistic relationship, an example of facultative service-resource mutualism. In the encounter, the bee receives nectar from the plant's blooms, which serves as a source of nutrition for the bee.

Conversely, facultative partnerships are advantageous to both parties and allow individuals to live independently of one another. Numerous mutualistic interactions involve situations in which one creature receives nutrition while another receives a service, such as cleaning or motility. Since plant materials are more difficult to digest than animal prey, many herbivores develop mutualistic gut bacteria to aid in this process. Herbivores' stomach microflora includes bacteria or protozoa that break down cellulose. Coral creatures and the diverse algae that inhabit them interact to create coral reefs. Most land plants and ecosystems rely on mutualistic interactions between mycorrhizal fungi, which assist in binding water and soil minerals, and plants, which fix carbon from the air. The relationship between Ritter's anemone and the Ocellaris clownfish's tentacles demonstrates reciprocity. A unique mucus on the clownfish's body protects it from stinging tentacles.

Another example is the goby, a fish that occasionally coexists with shrimp. The shrimp excavates and cleans a sand burrow where shrimp and goby fish live. Predators outside the burrow prey on the shrimp because it is practically blind. The goby will warn the shrimp if it is in danger by touching it with its tail. When this happens, the shrimp and goby quickly retreat into the burrow. Different gobies (Elacatinus spp.) clear out ectoparasites in other fish, supporting the possibility of mutualism. (nelson, Mutualism, commensalism, parasitism: Types of symbiosis with examples - science trends 2019)

Endosymbiosis
Endosymbiosis is the process through which one creature (the endosymbiont) coexists with another organism (the host cell) for mutual benefit. Many microbiomes are examples. Rhizobia, a nitrogen-fixing bacterium that lives in root nodules on legume roots; actinomycetes, a nitrogen-fixing bacterium that lives in the nodules of alder roots; single-celled algae found inside coral reefs; and bacterial endosymbionts that feed roughly 10%–15% of insects with vital nutrients. (Archibald, 2009) The host cell in an endosymbiotic relationship lacks some of the nutrients the endosymbiont supplies. As a result, the host creates some specialized cells that help the endosymbiont's internal growth activities. For instance, endosymbiotic interactions of lasting significance that broaden the spectrum of suitable habitats for life give rise to mitochondria and chloroplasts. The host mitochondrion and possibly additional endosymbionts that go through phases of vertical transmission are included in these genomes. Vertical transmission of symbionts refers to the direct transfer of a microbial symbiont from parent to offspring. a good illustration of vertical transmission A plant that has the virus in its seeds will produce infected offspring.

Commensalism[edit]
Commensalism is a symbiotic relationship where there are two organisms, in the same environment one organism is benefiting while the other is not significantly harmed or helped. Commensalism in Latin means the table of. This meaning goes back to the medieval period, where the people would enjoy the King's home for their benefit and the King would get nothing in return. The people could be called the commensals because they are benefiting and the King who be considered the "host's species" This type of symbiotic relationship is found in mostly taxa and habitats.

Commensalism and Disease
Commensalism has evolves through the loss of virulence or harmfulness. Low virulence and low transmission rates can easily lead to the extinction of a virus. Low virulence and high transmission rates are beneficial for virus propagation, while viruses with these features are more evolved and are more likely to develop into amensalism or commensalism with their hosts. For example human endogenous retrovirus W (HERV-W). The unique gene it produced, ERVWE1, which integrated into the human genome, encodes syncytin, which is essential for human embryo placentation.

Types of Commensalism
There are four types of commensalism. Inquilimsim is the type of commensalism where one species will use the other for housing, one species is benefitted since it has a place to live and the other remains unaffected. For example, a woodpecker drilling a hole into a cactus to be able to use it for nesting. Metabiosis is a type of commensalism where the host species, as mentioned in the definition, will create a suitable environment for the other organism, considered as the commensal. For example, hermit crabs and gastropod shells, the hermit crab will live inside the gastropod shell, which is empty, and protect its soft exoskeleton with it. Sometimes the hermit crab will also live and that shell and protect itself from predators. Phoresy is another the of commensalism where the commensal will latch on to a host, however the host will not be infected, the commensal latches on the host for transportation. The last type of commensalism is Microbiota, which is where microorganisms will colonize a particular tissue surface within a host. Normal microbiota is what it is called because it is compromised of bacteria. Thus, this relationship is commensalism, if the human body somehow gets disrupted in some kind of way and the bacteria overgrows there could be a problem.

Parasitism[edit]
Parasitism is a symbiotic relationship where one organism will benefit at the expense of harming the other organism. There are a few forms of parasitism. Endoparasites, ectoparasites, and parasitic castrotors. Endoparasites are the parasites that will get into the host and affect the host from the inside, then there are ectoparasites which are parasites that latch on and will affect the host from the outside. For example, a tick affecting a human by latching on and bitting the host, now the host is infected with Lyme disease. An example of endoparasites are tapeworms, inside a human. There are a good amount of parasitism and human interactions that are common.