Dendrotelme
The dendrotelme (plural: dendrotelmen, from the Greek δένδρον , "tree" and τέλμα , "puddle"), a variant of the phytotelme , is a water-filled tree cavity, which is popularly referred to as a "rabbit toilet". The micro Waters ( micro waters ) are exclusively of rainfall directly or by running down from the trunk water ( strain flow fed). They can be found in almost all larger tree species, but most frequently in the common beech ( Fagus sylvatica see figure on the right).
Types
There are two main types of tree hollows.
Woodpecker cave
So-called woodpecker caves are reminiscent of the brood caves of woodpeckers , hence the name. They are usually caused by injuries to the tree bark (for example breaking off a branch). The resulting hole fills with water so that the exposed wood core begins to rot. The cavity “eats” its way deeper and deeper into the tree due to rotting. The resulting tree cavity is not lined with bark. It is a good bit above the ground and has a capacity of one to several liters of water, depending on its size and location. As the putrefaction progresses, it can reach very large dimensions and lead to complete hollowing out of the trunk.
Cup cavity
So-called Napfhöhlen form the second group of Dendrotelmen. Due to the natural growth of the trees, these arise mainly in the often deep crevices at branches of the branches and forks and in the depressions formed by branches of above-ground roots and trunk adhesions. Since these caves do not result from injuries, they are completely lined with bark, which, however, gradually gets a coarser structure through the action of water. Cup cavities are mostly only a few centimeters above the surface of the earth. They can usually absorb larger amounts of water compared to woodpecker holes. In this type of cave, in contrast to the woodpecker caves that are almost completely dark, more light can enter. They are mostly in the penumbra. In addition, both types have the same effect that in the forest, due to the mostly thick “umbrella” made of foliage, the light outside the caves is also strongly dim.
Tree cavity habitat
There is a compact humus / sludge layer at the bottom of each tree cavity. These soil layers were created through the decomposition of organic material.
The animal species living in Dendrotelmen are divided into consumers and destructors . Producers are almost completely absent. In this case, the surrounding trees take on the role of producers. They supply the smallest body of water, mainly in autumn, with organic substances in the form of fallen leaves.
Water filling
The water level in the tree cavity is not constant, but fluctuates according to the constant change between evaporation and precipitation. Cup cavities in particular are particularly affected by this phenomenon. Because of their open location and large surface area, wind and sun are exposed to a large area and the evaporation can work unhindered. The degree of filling must therefore always be related to evaporation and precipitation.
Temperature conditions
The temperature of small bodies of water is particularly dependent on the environment. Warming up or cooling down usually follows the temperatures of the ambient air. The shallower a body of water, the more clearly the changes can be measured. The temperature of the tree hollows, both air and water, is subject to constant fluctuations.
Oxygen content
Another important ecological factor is oxygen . The oxygen content is decisive for the colonization of waters. There is a constant lack of oxygen in the deeper layers of the tree cavity and especially in the rotten layer. This results from the decomposition processes of organic material.
Nitrogen content
Another important ecological factor is nitrogen . The nitrogen content is decisive for the settlement of water bodies. There is a constant excess of nitrogen in the deeper layers of the tree cavity and especially in the rotten layer. This results from the decomposition processes of organic material.
PH value
The pH value is the result of the decomposition of organic material and rainwater that has entered. The degradation processes of wood or leaves, for example, release organic acids that shift the pH value into the acidic range. The rain has an influence on the cave water depending on its own characteristics.
Summary - living conditions
In the constant alternation between evaporation and precipitation, water-filled tree hollows represent periodic bodies of water in which the water level is sometimes exposed to extreme fluctuations. In general, tree hollows have low light input throughout. Even in the course of the day, there are significant differences in water temperatures. Large fluctuations can be found in the oxygen content, often at a level that is hostile to life for most organisms. Depending on the fallen leaves or the nature of the rain, the pH value shifts in random trajectories.
In summary, it can be said that difficult living conditions can be found in tree hollows , which have an inhibiting effect on settlement and require their inhabitants to adapt to a great extent.
Settlement - the Dendrolimnetica
Requirements for its residents
Water-filled tree hollows are extraordinary biotopes. They represent habitats that are exposed to a wide variety of changes in terms of the abiotic factors water filling, temperature, oxygen content and pH value. Despite extreme conditions due to constant changes in environmental influences, the biotope is populated by specific living beings, which are expected to be highly adaptable and have a wide range of ecological tolerances towards fluctuating environmental influences. One can therefore expect that the animals that occur are mainly Eurocean species.
colonization
The organisms living in tree hollows are summarized under the name Dendrolimnetica. Plants are seldom found in this biotope and living things are limited to a manageable number of single cells and insects. The abiotic factors mentioned are among the limiting factors here.
The main part of the Dendrolimnetica take the Protozoa . In this strain all classes of primal animals or protozoa are summarized. The free-living forms feed on bacteria, flagellates, algae, plant residues, other single cells, starch granules or fat droplets. Reproduction occurs asexually or vegetatively via cell division, the so-called conjugation . Cross-divisions of the animals result in a front and a rear daughter individual, which correspond exactly.
Protozoa are hardly restricted in their habitat and are widespread. They can be found in almost every body of water. They live in fresh water, in moss grass and in the sea.
to survive
The organisms of the dendrotelms must by nature be suitable for these living conditions and have developed certain adaptive abilities. It is known that unicellular organisms have extremely short development times. In addition, there is a rapid succession of generations due to the dichotomy and asexual reproduction. This enables quick and effective adaptation to the environment and guarantees rapid recovery after a population decline. If, for example, after a long period of drying out of the cave, the population should have been significantly decimated, the survival of a single individual would ensure the continued existence of the entire species.
In addition, the Dendrolimnetica fauna is a species that is able to form so-called permanent stages in the form of spores or cysts . Duration stages are forms of a cell or a living being that are resistant to influences such as B. Drying, are equipped with a resistant cover. These stages allow the animals to withstand extremely high as well as low temperatures. When favorable living conditions return, the vital functions awaken, the metabolism returns to normal in a short time and the living being resumes its normal activity.
Another advantage results from the distribution of cysts by animals. The wind can blow away the cysts. Every drop of water that gets stuck on a bird while it drinks at the den can contain hundreds of cysts. In this way, other animals also help with the transfer of the tree cavity dwellers to other habitats. The animals are therefore not necessarily bound to their tree cavity. If a cave silts up and becomes uninhabitable for the animals living in the water, they can temporarily survive as cysts. Resettlement in the other habitats is now possible through the transmission of wind or something similar. In this case, the high reproduction rate enables the new habitat to be developed quickly.
All of this makes these organisms extremely resistant to the fluctuating environmental influences of the dendrotelms.
literature
- Rudolf Drews, Hans-Peter Ziemek: Small water science . A practical introduction. 2nd revised edition. Quelle & Meyer Verlag, Wiesbaden 1995, ISBN 3-494-01226-1 ( Biological workbooks 41).
- A. Prange: Living conditions in the rabbit toilet. In: Hydrobiol. Vol. 24, Stuttgart 1993
- Ursula Rohnert: Water-filled tree caves and their settlement. In: Archives for Hydrobiology . 44, 1951, ISSN 0003-9136 , pp. 472-516.
- Barbara Dulitz: Life in the Hasenklo. In: teaching biology. 20, issue 216, July 1996, ISSN 0341-5260 , pp. 25-26, 31.