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Coexitence....

Deutschland

Peru Rainforest Amazon Pachitea Llullapichis Panguana Species Diversity : Koexistenz

Ecological investigations in tropical rainforests have repeatedly focused on the question as to how so many species can exist side by side, since resources are limited in any ecosystem. The secret lies in the specialization in space, time, food and reproduction. The tropical rainforest with the levels offers its inhabitants a third dimension with many places to hide, sources of food and places to breed.

Science has only begun to undertake a count of the species living in the rainforest in the last couple decades, as well as trying to sort out the extremely complex network of relationships. It then becomes clear that tropical rainforests are "more than just restaurant and apartment" (Whitmore, 1990).

An example might be the dependency of most rainforest plants on animal pollinators. Pollen carried on the wind plays a very small role in this environment. In all tropical rainforests one can find similar methods (syndromes) of attracting certain pollinators such as birds, bats, moths, beetles, bees; all of the animal groups require their own flower construction. Bird flowers and built to be stable, loudly colored and stick out of the general sea of leaves or don't flower at all until a tree loses its leaves.

Bat flowers open at night, are usually white, sticky and often have a clearly acidic or moldy small. The transfer of pollen to the bat can occur in two ways. Either the flower is formed like a deep cup so that the pollen gets stuck on the head of the bat, or the plant offers its pollen on shaving brush-like leaves of powder. In this case the pollen gets caught on the chest of the bat. Bat flowers also stick out of the leaves.

The German research couple Dagmar and Otto von Helversen discovered an "acoustic cat's eye" during research in Middle America on the Liana Mucuna hotonii. One of the five petals of the flower that stood straight up like a two-centimeter long flag was marked with a small triangular impression, which served bats as a help in recognition. The sound of the bat's sonar got magnified in the impression, so that it was sent back to the animal with a higher intensity. The flag still throws back an intense echo when the bat is not directly in front of the flower, but at a position of up to 40 degrees off.

The moth flowers also open at night. They usually smell sweet, are delicate and have a very long perianth tube, in which the long snout of the butterfly is stretched forward to the source of the nectar. Beetles land and crawl relatively heavily on their flowers. Thus beetle flowers tend to be robust and bowl-shaped. They often smell pleasant and usually sit in the middle of the leaves. Bee flowers with a moderately broad spectrum of flower forms are common in the rainforests. They open and close according to the time of day and are usually very colorful. They also often have a so-called nectar guides that is only recognizable in the ultraviolet light that is visible to bees. Bee flowers, such as orchids, are often equipped with a landing platform.

The dissemination of seeds by animals is another example that demonstrates the dependency between animals and plants. Bird fruits can be differentiated according to whether they are eaten by exclusively fruit eaters, or whether the birds also eat other things. Typical fruit eaters prefer large, nutritious fruits with large seeds. Birds that eat fruit as just one part of a varied diet prefer small fruits with a lot of water and small seeds.

The importance of fish as distributors of plant seeds has only been research in the past few years. When the water is high fish take in fruit and seeds in the flooded areas. When the water recedes the fish pull back into the lagoons that are left and life primarily off of their fat reserves. Except for the fact that research on Peruvian monkeys of various species showed a preference for yellow fruit, no particular fruit characteristic seemed important for either mammals or fish.

Many examples of symbiosis, mutual dependence between different organisms, show the common development (co-evolution) of plants and animals. Lichens - a symbiosis of fungus and algae - are seen everywhere in the Amazon. Ants find living space and food in the trunks of defenseless trees and protect them with their lives. Even climbing plants and epiphytes don't stand a chance of settling in on trees protected by ants. The frog Lithodytes lineatus is allowed to live in the underground nests of the leaf cutter ant Atta cephalotes. It eats insects that could endanger the nest or the brood. It is then tolerated by the Atta soldiers that give it sanctuary and even an underground source of water for the tadpoles.

Ants living in trees put epiphytes seeds into the floor of their nests. They bring animal dung and thus fertilize the plants. An ant garden is created in which the epiphytes thank the ants by producing sugary secretions.

With a loud rush half of a tree crown crashed through the ceiling of neighboring trees, hits a vertical aisle and hits the ground with a thump. For a moment the forest is completely silent, and then the Aras (Ara) begin to protest. A year later I had great difficulty in finding the site of the crash again. The wood is molding. Fungi are working and secondary vegetation has covered many tracks. The bark of the rest of the crown comes off with the slightest touch and reveals a huge number of animals. Insect larvae, beetles, springtails, millipedes and spiders all run around in surprise. Termites have done their job well in places and a scorpion hides in their "sawdust".

Various organisms so concentrated in such small quarters in the middle of a dark primary forest is almost impossible to find. The fall of a dilapidated crown in the forest should in fact be a catastrophe for the biotop. Catastrophe means the disappearance of species, but this equation doesn't seem to hold here. In fact this scene of destruction is a magnet for plants and animals that don't exist in the shadowy, intact primary forest, or at least not as densely.

Trees only reach a certain age, even without the heavy epiphytes, lightening or windstorms. They die, fall down and create a hole in the forest. Such holes bring light in which tree starts that had been languishing can grow into young trees and eventually into tree giants. The forest is not static; it is in a constantly changing balance. The death of an old tree, sprouting seeds, growing trees, dying trees; as a result of this dynamic the forest is a mosaic of spots that are in various phases of development.

Just as the way one can trade out the individual pieces of a mosaic, the character of individual parts of the tropical forest can change. If the clearing in the forest from a fallen tree is small, the embryos of the so-called climax species shoot up. They come from the trees directly around them of often wait for years in the dark to grow. Then they grow up, yet the species composition doesn't change at this stage. If the clearing is large enough that sunlight reaches the ground directly however, it will be covered with fast-growing, light-loving pioneer species. The ant tree (Cecropia) is one of the first trees to settle in when the forest is damaged somewhere. Fungi thrive under the large, shade-giving leaves, and hordes of flies are attracted when the fungi begin to decay. Pipe frogs (Adenomera), that cannot handle direct sunlight, can comfortably catch flies in the shade. Ctenid spiders get wind of them and go hunting the little frogs. A small, very diverse life form community is thus created in the shade of the pioneer species. Pioneers are not long-term, however. Not only the animals mentioned above thrive in their shade, but also the embryos of climax species. When the pioneers die the climax species take over and continue the next growth cycle of the stand. This process is called succession.

The constant alternation between climax and pioneer species leads to a to-and-fro of conditions on a certain spot, but doesn't change the forest as a whole. Thus we speak of a mosaic cycle balance.

These centers, which provide provisions, are to be found everywhere throughout the tropical rainforest. They make it quite clear that natural "catastrophes" do not lead to a reduction in diversity in the long run, but are rather a pillar of diversity.

 

Text und Fotos © Andreas Schlüter 2003-2004