AMENSALISM: CHARACTERISTICS, EXAMPLES, DIFFERENCES WITH COMMENSALISM - BIOLOGY - 2025

The amensalismo is a type of negative interspecific interaction, ie, is a type of interaction that occurs between different organisms and species that has negative effects on the number of individuals of the population of one of the two interacting species.

Like predation and parasitism, amensalism is a type of one-way interaction, meaning that one of the two interacting species affects the other, but not vice versa.

Photograph of an Iberian ibex (Source: Benjamín Núñez González, via Wikimedia Commons)

This type of interaction is not as commonly known as predation, competition, commensalism, or mutualism. It was described in the early 1950s by the ecologist Odum and later revised by other authors.

In 1952, Paul Burkholder defined amensalism as a - / 0 interaction, in order to describe the negative (-) effect of one species on the other and the neutral (0) effect of the negatively affected species on the other.

The term is often confusing or ambiguous in some cases, since even in clear examples where one of the interacting species is obviously affected by the relationship, the possibility that the other species is also affected in some way is not completely excluded.

characteristics

Amensalism is a type of interaction between two different species and is considered a type of "asymmetric" symbiosis, since the interacting individuals have very different sizes or levels of force.

The species involved in an amensal relationship are called "amensales", just as there are "commensals", "competitors" and so on.

In some specialized textbooks it is described as a relationship (- / 0), which means that, during the interaction, the first species negatively impacts the second without receiving any benefit, but the latter has no effect on the first.

It is easily confused with other competitive relationships and is sometimes described as a relationship without "coevolutionary" effects (where the two species evolve together due to their interaction).

Amensalism is a type of interaction that can last a very long time, as long as the negative effects of it do not lead to the extinction of the non-favored species.

However, mathematical models used by ecologists to predict and study amensalist relationships have shown that although amensalism is a relatively stable process, it may be the case that the negatively affected species disappears.

This means that some amensalistic relationships between species can be a "soft" or "prolonged" form of predation, since one of the two species contributes to the disappearance of the other, although without receiving any benefit in return.

Examples of amensalism

Amensalism is not an easy type of interaction to verify and, in general, ecologists who are in charge of the study of the relationships between species that live in common sites use some experimentation techniques to verify what type of interaction it is.

Some examples of amensalism have been described by Veiga (2016). Among these, the author mentions the interaction between beetles of the genus Timarcha and the mountain goat or the Iberian ibex (Capra pyrenaica), which feed on the same type of bush.

Photograph of a beetle of the genus Timarcha (Source: Paucabot via Wikimedia Commons)

When bush goats and beetles are experimentally separated, the number of beetles increases considerably (about 4 times), whereas when bush beetles and goats are separated, the number of goats visiting the sites does not increase. shrubbery.

This phenomenon is due to the fact that goats eat a large part of the leaves (leaving little food for the beetles) or accidentally eat some of these insects while feeding, which causes the tithe of the beetle population (as an effect secondary).

This interaction is known as amensalism because the presence of the beetles has little or no effect on the goats, but they have a negative effect on the population of the insects in question.

As well as this, the interaction between other species of insects and other herbivorous animals (which feed only on plants) are good examples of amensalism, where the fact that the herbivorous animal and the insect have sizes, life cycles and conditions could be generalized. markedly different ecological

Other examples

Although amensalism is usually confused with other types of interspecific interactions such as competition or commensalism, there are some more or less clear examples of amensalism in nature.

An additional example proposed by Veiga (2016) is that of the "interaction" between bees and bumblebees and the arrangement of their nesting sites (honeycomb formation).

It has been experimentally shown that bees are indifferent with respect to the settlement site of their combs, while bumblebees are not able to settle in places that have been previously used by bees, although in previous seasons.

This relationship is described as amensalism, since for bumblebees there is a negative effect that is related to the previous presence of bees in the sites where the latter intend to establish themselves, while for bees there is no type of effect that is related to the presence of bumblebees.

Something similar happens with some species of birds and with nesting, but in relation to the size and arrangement of the nests.

Mussel beds

Mussels are bivalve animals that can be found forming a kind of "beds" on some marine and coastal territories. Large numbers of marine organisms feed on these "beds" and other organisms that are associated with such types of ecosystems.

Photograph of a "bed of mussels" (Source: Gastón Cuello via Wikimedia Commons)

Some researchers consider that there is a relationship of amensalism between mussels and the species that coexist with them in the water that surrounds them (which feed on suspended particles).

Birds in the Galapagos Islands

An amensalist relationship has also been reported for birds of the genus Sula (pike birds) in the Galapagos Islands:

The blue-footed Sula species (Sula nabouxii) is displaced from its nesting sites by the Nazca booby (Sula granti), but the latter does not suffer any type of effect due to the presence of the blue-footed booby.

Differences with commensalism

To understand what are the differences between amensalism and commensalism, it is necessary to review what commensalism is.

Commensalism

Clown fish and anemone

Commensalism is also a type of ecological relationship that occurs between different species, where one of the species involved benefits from the other without negatively impacting it.

There are good examples of commensalism in both the animal and plant kingdoms, and it has also been described for some relationships between bacteria.

An example of commensalism in the animal kingdom includes certain species of pseudoscorpions that can temporarily adhere to a great variety of arthropods, which they use to mobilize.

This relationship means a point in favor of scorpions, since they manage to move from one side to another, but it has no effect on the insect on which they are transported, since they do not interfere with any of their normal physiological processes or provide any apparent benefit.

Commensalism, like amensalism, is also a unidirectional relationship and does not imply the coevolution of the interacting species.

The definition of commensalism is difficult to specify, since the net effects of interspecific interactions can vary greatly in time and space. Also, the demonstration of a commensal relationship is not trivial at all, but the same is true for amensalism.

From a loose point of view, a commensal relationship can be defined as a relationship where one of the species benefits and the other is not affected by the interaction, or it can be slightly affected, both positively and negatively.

Differences

The main difference between amensalism and commensalism is that, in an amensalist relationship, one of the participating species is negatively affected (- / 0); while, in commensalism, on the contrary, the effect of the interaction between two species is beneficial for one of these (+ / 0).

For example, in the relationship between epiphytic plants and trees, say between a large tree and an air carnation or tillandsia, the epiphytic species benefits from the support provided by the tree's branches to establish itself.

Meanwhile, the tree does not receive any benefits, but it is not adversely affected by the presence of tillandsia.

In the case of phenomena known as “allelopathies”, one plant negatively affects another by releasing secondary metabolic products to the rhizosphere (the portion of the soil associated with plant roots).

However, the presence of the plant that is affected has no effect (neither positive nor negative) for the plant that secretes the substance, which is why it is considered an amensalism relationship.

Another difference between commensalism and amensalism, although perhaps not as significant, is the fact that amensalism has been more widely described between considerably different species (at least in relation to their size and capabilities).

In commensalism, by contrast, it has not been determined that there is a relationship between the size or capabilities of the interacting species.

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