Biological interaction

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Biological interactions result from the fact that organisms in an ecosystem interact with each other, in the natural world, no organism is an autonomous entity isolated from its surroundings. It is part of its environment, rich in living and non living elements all of which interact with each other in some fashion. An organism's interactions with its environment are fundamental to the survival of that organism and the functioning of the ecosystem as a whole.

In ecology, biological interactions are the relationships between two species in an ecosystem. These relationships can be categorized into many different classes of interactions based either on the effects or on the mechanism of the interaction. The interactions between two species vary greatly in these aspects as well as in duration and strength. Species may meet once in a generation (e.g. pollination) or live completely within another (e.g. endosymbiosis). Effects may range from one species eating the other (predation), to both living together with mutual benefit (mutualism).

The interactions between two species need not be through direct contact. Due to the connected nature of ecosystems, species may affect each other through intermediaries such as shared resources or common enemies.

[edit] Interactions categorized by effect

Effect on X	Effect on Y	Type of interaction
0	0	Neutralism
-	0	Amensalism
+	0	Commensalism
-	-	Synnecrosis
+	+	Mutualism
+	-	Predation or Parasitism

Some types of relationships listed by the effect they have on each partner. '0' is no effect, '-' is detrimental, and '+' is beneficial.

Terms which explicitly indicate the quality of benefit or harm experienced by participants in an interaction are listed below:

Neutralism is a lack of interaction. Since all species sharing an environment interact in some way, a complete lack of interaction is rarely seen in nature. However, the term can also signify a relationship in which each species derives neither benefit nor detriment to any measurable degree.

Mutualism benefits both populations. It is often non obligatory or temporary.

Synnecrosis is detrimental to both species. It is a rare and necessarily short-lived condition as evolution selects against it.

Amensalism is detrimental to one species and neutral to the other.

Commensalism benefits one organism and the other organism is neither benefited nor harmed.

Predation is an interaction between organisms in which one organism captures biomass from another. It is often used as a synonym for carnivory but formally also includes herbivory, parasitism, and parasitoidism.

It is important to note that these interactions are not always static. In many cases, two species will interact differently under different conditions. This is particularly true in, but not limited to, cases where species have multiple, drastically different life stages.

[edit] Interactions classified by mechanism

Symbiosis is an obligatory relationship between two populations. Partners in a symbiotic relationship are constantly in contact with each other. Often one lives inside the other. It often implies mutualism, but most formal definitions also include other types of relationships like parasitism and commensalism.