Ant plant
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Under ant plants or Myrmekophyten one understands plants with ants a symbiotic received connection. The plant offers living space ( domatia ) and sometimes also food. In return, the ants either offer protection against predators or against growth by epiphytes ( myrmecophylaxis ) or they provide food themselves ( myrmecotrophy ). Many myrmecophytes are tropical plant species.
The ant plants do not include plants whose seeds are spread by ants ( myrmecochory ), e.g. B. Larkspur , snowdrop and celandine . Plants whose flowers are pollinated by ants ( myrmecophilia ) also do not belong to the ant plants .
Myrmecophylaxis - protection by ants
Protection against young and vulnerable parts of plants is of decisive importance for all plants. In order to protect themselves from predators, plants have developed a wide variety of defense mechanisms in the course of evolution , such as chemical defense substances as well as spines and thorns .
In the tropics and subtropics, another very effective defense strategy has developed for some plant species : protection by ants. This form of the relationship between ants and plants is known as myrmecophylaxis. The plant provides the ants with living space and food and, in return, is protected by the ants from predators and competing plants. The form of community between ant plants and ants is very different in the various myrmecophytes. Because while some ant plants are only occasionally visited by ants, other genera are constantly colonized by ants. The latter are highly specialized symbioses in which one partner would no longer be able to survive without the other. The form of the "living space" and the supply of food to the ants by the plant is also different for the various taxa . The ant plants provide the ants with living space in the form of cavities called myrmecodomaties. Myrmekodomatien are found in the different genera in the various organs ( shoot , leaf or root ) of the plant.
The form of the food that is produced by the plant in order to attract the ants or to bind them permanently to itself is also very different between the different genera. Many myrmecophytes have extra-floral nectaries , which are mostly found on the leaves, but in some species also on the shoot, the buds and the outside of the sepals . Extra-floral nectaries are nectar glands that, in contrast to the floral nectaries, are located outside the flower. The plants excrete nectar , which consists of an aqueous sugar solution, through the extra-floral nectaries . In many ant plants, the nectar contains sugar ( mono- and disaccharides ) as well as amino acids , proteins and other chemical substances. For numerous species of ants that visit or live permanently on ant plants, the extra-floral nectaries are an important source of nutrition. Many types of ants that use the extra-floral nectar of the myrmecophytes as food show extremely aggressive behavior towards herbivores and other insects that differ from the nectar of the Ant plants feed and chase them away. This is how the ants protect the myrmecophytes from eating damage.
With highly specialized symbioses between ants and myrmecophytes, the ants do not leave the plant all year round and constantly guard it from predators. Some species of ants that permanently colonize ant plants even protect them from competing plants growing near their plant by working them with their mouthparts until they eventually die. The ants also remove epiphytic growth and climbing plants that grow on or on the ant plant.
In particularly highly developed symbioses, however, the plants not only provide the ants with food through extra-floral nectaries, but also in the form of eating or fodder bodies. These corpuscles are very protein and fat-rich small structures that are collected by the ants and mostly fed to the larvae . In many species, the corpuscles arise on the leaf organs.
Some species of ants that colonize plants also receive food from the plant through another form. They live in "symbiosis" with leaf , root or scale insects , which they keep on inhabits plant, d. H. guard and "milk". Because these penetrate with their mouthparts into the phloem of the plant and feed on its carbohydrate-rich juice. However, since they are primarily dependent on the amino acids of the phloem fluid to meet their protein requirements, they absorb much more sugar than they need and excrete this in the form of a sugary solution ( honeydew ) through the anus. After all, the honeydew serves as food for the ants. In return, the aphids or scale insects are tended by the ants and protected from enemies.
Myrmecotrophy - feeding by ants
Myrmecotrophy is a form of partnership between ants and plants, in which the plant provides the ants with nesting space and the ants provide the plant with nutrients.
This type of partnership is particularly common in epiphytic plants in the tropical rainforest , as it is particularly difficult for these plants to absorb sufficient nutrients.
Some ant plants that enter into such a partnership with ants have domatia, similar to the myrmecophytes of a myrmecophylaxis, in which the ants find suitable nesting spaces. These plants are mostly colonized by small, less aggressive ants, which make an important contribution to the nutrition of the plant. Because in the domatia that are colonized by the ants, organic waste such as B. animal corpses, vegetable waste and excrement or are even stored in separate chambers. The plant, in turn, is able to absorb the nutrients contained in the organic waste. The form of nutrient absorption from the organic substances depends on the respective plant species. Some plant species such as B. Dischidia rafflesiana absorb nutrients with the help of roots that grow into the cavities populated by the ants. Epiphytes of the genus Hydnophytum and Myrmecodia show another way of absorbing nutrients, because they are able to absorb nutrients through the porous walls of the cavities.
In addition to supplying the plant with nutrients, these myrmecophytes also benefit from their partnership with the ants. Because these not only provide the nutrients for the plant in the form of organic material, but also contribute to the spread of the plant by carrying its seeds with them (myrmecochory). Since the ants are tree-dwelling species, the seeds of the epiphytes are often dropped directly in suitable locations. The ants also have decisive advantages from such a relationship, because they are provided with suitable living and nesting spaces in the myrmecodomata of the plants. In addition, some plants have extra-floral nectaries that help feed the ants.
Both partners of a myrmecotrophy thus derive considerable advantages from this connection. In many cases, however, this partnership is not required (optional), as both partners would be able to survive on their own. Due to the additional source of nutrients, a colonized plant often has a decisive competitive advantage over competing plants that grow in the same location.
Ant gardens
Ant gardens are characteristic collections of epiphytes that grow on ant nests or the roots of which are colonized by ants.
In contrast to epiphytes, which provide myrmecodomata as a nesting space for ants, ant gardens usually only contain plants that do not develop myrmecodomata. Ant gardens arise such as B. in Codonanthe uleana in that the plants develop adhesive roots with which they attach themselves to the trunks of trees. Ants (in Codonanthe uleana ants of the genus Azteca and Camponotus ) attach soil to these roots . The plants can take root in this soil material and thus hold it together. In this way, extensive structures emerge that consist of rooted earth material and often mushrooms. These serve as stable nests for the ants and enable the plants to live epiphytically on trees. Without the help of ants z. B. Codonanthe uleana is able to settle on the ground, but not on other plants. However, ant gardens can also be created in another way. Some species of ants build so-called cardboard nests on trees. These nests consist of a wide variety of materials, such as fine wood flour or decomposed and living plant fibers. During the nest building, the ants also carry seeds from epiphytic plants like z. B. Plants of the genus Hoya in their nest. The seed finds nutrients here and germinates out of the nest. The ant's nest is stabilized by the roots of the plant and kept on the host tree.
In ant gardens, different species of ants often appear as partners of the plants. For example, ants of the genus Camponotus and Crematogaster both live in symbiosis with Hoya elliptica . In some cases, even several species of ants colonize an ant garden at the same time.
Some plants found in ant gardens, such as B. Plants of the genus Codonanth , it is also known that they also provide their symbiotic partners with food in the form of extra-floral nectaries and seeds with elaiosomes .
Elaiosomes are nutrient-rich, oil-containing appendages to plant seeds, the composition of which is specially adapted to ants and their nutritional needs. They therefore serve as a lure and reward to induce the ants to procure and thus to spread the seeds. As soon as the seeds are found by the workers, the complete seed with elaiosome is transported to the nest, although the seed itself is not suitable as food for the ants. In the nest of the ants, or on the way there, the elaiosome is eaten away by the workers. The now elaiosome-free seed is either left lying on the way to the nest or disposed of in the nest in the waste chamber. The spread of the seeds by ants (myrmecochory) means that the seeds of epiphytic plants reach suitable locations, such as the ants' nest, where they can find enough nutrients to germinate.
Of some species of ants that show aggressive behavior, such as B. Ants of the genus Camponotus are also known to defend their ant gardens. There is a close symbiosis between ants and epiphytes that live together in ant gardens, which offers several advantages for both partners. This partnership enables the plants to live epiphytically on trees. Their seeds are spread by myrmecochory in suitable locations and they are sometimes even given protection by the workers. The ants, on the other hand, receive food and a safe nesting place.
These interactions have arisen several times independently of one another in different plant groups and are mostly facultative, i.e. voluntary (especially in myrmecophylaxis), but sometimes also obligatory, so that both partners are absolutely dependent on each other.
Devil's garden
The Devil's Garden ( Kichwa : Supay chakra ) are monocultures of the red plant Duroia hirsuta created by ants in the rainforest of the Amazon region . Competing plants of Duroia hirsuta are killed here by poison injections from the ants.
literature
- IW Bailey: The anatomy of certain plants from the Belgian Congo with special reference to myrmecophytes. In: Bulletin American Museum of Natural History. Vol. XLV, 1922, pp. 585-621.
- Georg Zizka: Plants and ants. Partnership for survival. (= Palm garden. Special issue 15). Frankfurt am Main 1990, OCLC 23023445 .
- Klaus Dumpert: The social life of ants. Berlin 1978, ISBN 3-489-65736-5 .
- Bert Hölldobler, Edward O. Wilson: In the footsteps of the ants. Springer, 2013, ISBN 978-3-642-32565-6 , pp. 351ff