Mutualism is ... Types of mutualistic relations

Mutualism is a biological interaction that promotes the survival and growth of both species-partners. In other words, it is a form of symbiosis. Lichens are a classic example illustrating what mutualism is.

Another example is the relationship between legumes and nitrogen-fixing bacteria in the nodules on their roots. Mutualism is also some close interrelationships of pollinators with pollinated plants, for example lepidoptera Tegeticula yucasella and yucca.

Optional and obligate mutualism

It is necessary to distinguish between these two concepts. Both the obligate and facultative mutualism are mutually beneficial cooperation. Interaction in this case is useful for one and the other kind. However, in the second case, each species can exist in isolation. Obligatory mutualism is a must. This means that organisms can not exist separately.

Mycorrhiza

One of the most interesting and important examples from the point of view of ecology of the phenomenon that interests us is the interactions that exist between fungi and vascular plants. The roots of most of these plants form complex structures with fungi. These structures are called mycorrhiza. Without it, normal plant growth would not be possible. Mycorrhiza, apparently, played a key role in settling their land. Since ancient times, mutualism (symbiosis) was widespread.

Mycorrhizal connection

The more we learn about them, the clearer their importance becomes for vascular plants. In many species, nonmycorrhizal individuals are rarely found in nature, even if their growth is possible without fungi, with careful selection of the conditions of growth. Most vascular plants are "double" organisms in the same sense as lichens, although this duality, as a rule, is invisible over their overground part. According to soil scientist from Wisconsin University S. Wilde, the tree extracted from the soil is only part of the whole plant, surgically separated from its absorbing and digestive organ. In most plants, fungi play a vital role in the assimilation of phosphorus and other essential nutrients.

Fungi that form mycorrhizas with most plants belong to zygomycetes. This type is called endomycorrhiza. It is typical for most grasses, bushes and trees. Some groups of conifers and dicots, mostly trees, form mycorrhizas with basidiomycetes, as well as some ascomycetes. In this case we are talking about ectomychorisis. Sometimes it is very specific: one species of fungus interacts only with a certain type of vascular plant or with a group of related species. It is known, for example, that the basidiomycete of Boletus elegans is associated only with larch (Larix) from conifers. Other fungi form mycorrhizas with forest species more than a dozen genera. Ectomycorrhiza is particularly characteristic of relatively poor species of trees living in high latitudes of the Northern Hemisphere or in the highlands.

Acacia and ants

The most complex examples of mutualism are found in the tropics, where the diversity of organisms is much higher than in temperate regions. So, in the tropics and subtropics acacia (trees and shrubs of the genus Acacia) are widespread. The relationship between certain species of these plants on the plains of Mexico and Central America and the ants living in their thorns is a wonderful example of complex interactions between animals and plants. Especially visually they are traced for ants of the genus Pseudomyrmex.

In these acacias at the base of each leaf there is a pair of swollen spines, the length of which is more than 2 cm. The petioles have nectaries, and at the ends of leaves there are small nutritive organs called Belt bodies. Ants live inside hollow spines, feeding on nectar sugars and Belt bodies that contain fats and proteins. Acacia grow extremely rapidly and is especially characteristic of disturbed areas, where competition between fast-growing colonizing plants is often very intense. Thomas Belt first described the relationship between Pseudornyrmex and these trees in his book The Naturalist in Nicaragua, published in 1874.

Other types of mutualistic relations

There are many other types of relationships linking the organism in which mutualism manifests itself. This, for example, trees in the forest (as well as grass), which are often spliced with their roots. As a result, nutrients are transferred from one plant to another in a complex and completely unexpected way, and the survival of a species in a particular locality is literally dependent on the presence of another with which it forms such a connection. Tree stumps can live indefinitely, although they are deprived of photosynthetic organs, because they are fused to other individuals and can receive nutrients from them. Some diseases, for example the oak wilt in the Midwest and the East of the USA, can also be transmitted through such root "vaccinations".

As you can see, mutualism is often a phenomenon in nature. It is a special form of symbiosis.