por Mutualism is a type of positive (+/+) interspecific ecological relationship (which occurs between individuals of different species) in which the two species involved benefit from the interaction.
Certain authors consider that mutualism can be described as a kind of symbiosis, cooperation or facilitation, since one of the interacting species offers a «service» that the other species lacks, and this, in turn, provides a » reward” in return.
Mutualistic relationships are highly diverse interactions, since there are some of them that are forced (one species cannot live without the other and they have joint evolutionary histories), while there are others that are very loose and some are even unpredictable.
For ecologists it is not always easy to determine what kind of relationships exist between natural populations and their members, and mutualism is no exception, since it is not always possible to determine what is the benefit of one association or another.
Good examples of mutualistic relationships can be described in animals and plants. For example, zooxanthellae exchange carbohydrates for nutrients in the coral they host, and plants produce seeds surrounded by fruits, which provide food for dispersing animals.
It is important to take into account that mutualistic relationships are particularly important for the reproduction and survival of many plant species and, furthermore, they contribute to nutrient cycling in practically all ecosystems.
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Characteristics
Interspecific relationships are classified as positive (+), negative (-) or neutral (0), according to the result of the effects that these interactions have on each of the individuals that participate.
In this sense, mutualism is defined as a positive relationship (+) and is recognized as an essential type of interaction for many natural ecosystems. Mutualism can be species-specific or generalist, depending on the specificity of the interaction.
Most of the mutualistic relationships imply, as previously mentioned, an exchange of “goods and services”, since it is a type of interspecific relationship where the two interacting parties benefit.
Thus, it differs considerably from competition, predation, neutralism and amensalism, for example, where the relationships imply a loss on the part of one of the species involved or where there is also a kind of «indifference».
Mutualistic relationships positively affect the ability of individuals to have fertile offspring of the participating species.
In addition, it is very common to observe that the traits of the interacting species evolve together to maximize the benefits acquired during the interaction, and this is possible through mutations, selection, and genetic recombination events.
Guys
As is true for other interspecific relationships, mutualistic relationships can have different degrees of dependency, with obligatory relationships and facultative relationships being found.
In this sense, in nature it is easy to run into mutualistic relationships where species are under forced-forced interactions; obligatory-facultative or facultative-facultative.
forced mutualism
This type of mutualism implies that the interacting species would become extinct in the absence of the mutualistic relationship. The relationship is not only beneficial, but rather necessary.
In other words, what the concept of «forced» means is that both species have evolved to such a point that they are completely dependent on each other for their survival, since they cannot live without the benefits that result from their interaction.
Obligate mutualistic species represent one of the best examples of coevolution, and this type of interaction is very commonly observed in symbiotic associations, such as that found in lichens, which are made up of algae and fungi.
facultative mutualism
Facultative mutualism is one where the interacting species can coexist in the absence of the interaction and are, in reality, what is known as “opportunistic mutualists”, which take advantage of the interaction depending on the conditions in which they find themselves.
It is very common to find facultative mutualisms that are not species-specific, since they rather imply a somewhat «fuzzy» relationship, which can occur between different species and even between mixtures of species.
trophic mutualism
This type of mutualistic relationship is key to most of the ecosystems that exist. The term refers to an interaction between species (which can be species-specific or generalist) where an exchange of nutrients occurs, that is, where «goods and services» are in the form of energy and food.
Species that interact in trophic mutualism complement each other for the sake of obtaining food rewards, which is why this interaction is also known as resource-to-resource mutualism.
It has been seen especially in symbionts, but it also occurs between autotrophic organisms (that form their own food) such as plants, and heterotrophs (incapable of producing their own food), such as animals.
defensive mutualism
Defensive mutualism is one that occurs between two species where one of them provides shelter and food to the other in exchange for defense against predators, parasites or herbivores (depending on the species).
It has been well documented between plants and fungi, for example, where the fungi receive food and shelter from the plants, while the former are protected from herbivorous animals by the segregation of repellent or toxic substances from the fungi.
It has also been classified as a defensive mutualistic relationship that takes place in marine ecosystems between some species of fish and crustaceans, which help to eliminate parasitic species from the skin and gills of other larger fish species.
Small fish and crustaceans benefit from this interaction, since the parasites they remove from the surface of the larger fish species with which they interact serve as food for them.
dispersive mutualism
Although it is perhaps a very specific type of mutualism between plants and animals, it is one of great importance.
As its name indicates, dispersive mutualism is one where some animal species (vertebrates or invertebrates) participate in the dispersal of pollen grains or seeds of plant species.
In return, the flowers offer their succulent dispersers rewards in the form of nectar, fruits, pollen, shelter, breeding and/or oviposition sites, etc.
In the case of seed dispersal, mutualistic dispersal relationships are usually quite loose or non-specific, given that, for example, a bird species can feed on more than one type of fruit or that one type of fruit can be the food of multiple species of birds.
The plant-pollinator relationship, on the other hand, tends to be a bit more specialized, since there are species-specific pollination cases in which the flowers are specially adapted to the characteristics of the pollinated or vice versa.
There are some seed dispersers that are actually «predators», since they feed on these seeds, but they facilitate the dispersal of those that they drop along the way or that they store in certain places.
examples
The most common examples of mutualisms are:
– Pollination
Animal-mediated pollination and seed dispersal (plant-animal relationship), essential not only for natural ecosystems, but for the human race per se.
Ficus and fig wasps
An example of an obligate mutualistic relationship is the one that takes place between some trees of the genus Ficus and fig wasps. Most of these trees are pollinated by these wasps, which are completely dependent on the trees for their reproduction and sustenance.
It is a clear example, not only of an obligatory mutualistic relationship, but also of the benefits that a mutualism has on the reproductive efficiency or success of the species involved.
Wasps participate in the reproduction of fig trees since, in search of a place to deposit their eggs, they can visit several flowers and take their pollen grains from one flower to another.
The flowers are the preferred oviposition sites and it is where the larvae hatch, feed on the seeds of the tree and then mate, to repeat the cycle.
The birds and the flowers
Like bees, some birds feed on the nectar of flowers, transporting pollen from one plant to another, which favors pollination.
– Nitrogen fixation
The mutualistic relationships of nitrogen fixation that occur in agroecosystems and in desert areas (plant-microorganism relationship), where through their roots, plants interact with microorganisms that help them assimilate nitrogen from the soil, obtaining food from the plants.
– Microorganisms in hydrothermal vents
The relationships between microorganisms that inhabit hydrothermal vents in the depths of the oceans.
– Animal-animal relations
oxpeckers and rhinos
Oxpeckers are birds that perch on rhinos and eat the ticks and other parasites that live on the skin of these mammals. In this relationship, both benefit as the birds get food while the rhinos get a pest control service.
The tarantula and the boqui toad
The boqui toad feeds on parasites that could affect tarantula eggs. In return, the tarantula allows you to live in its territory.
– Plant-animal relationships
Plant-animal relationships where some animal species “protect” some plant species from attack by other herbivorous animals in exchange for food and shelter.
Anemones and clown fish
The anemones, with poisonous darts, protect the clownfish from potential predators; the mucus on the skin of clownfish protects them from this sting. In turn, this species of fish protects the anemone from predators.
The spider crab and the algae
Spider crabs spend much of their lives in areas where the water is shallow, which increases the chance of being seen by predators.
However, on the back of these crabs, there lives a certain type of algae that acts as camouflage for the animal. In exchange, the plant gets a habitat to live in.
The yucca moth and the yucca plant
The yucca moth is involved in the pollination process of this plant. In return, the plant offers protection to the moth eggs and food to the larvae, once they hatch.
The ants and the acacias
The ants lay their eggs on the thorns of acacia trees. In exchange for the protection offered by these plants, the insects protect the acacias from herbivores.
– Microorganism-animal relationships
The…