Key type

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As a key type (according to the English. Name "Keystone Species", origin. " Keystone -Art") in which it is ecology a kind referred to in comparison to their low frequency a disproportionate impact on the biodiversity exerts a community. Even though key species can occur at any trophic level , they are mostly predators. Due to the feeding pressure of the key species, the population density among the prey animals is reduced to such an extent that the competition between the prey species decreases and the coexistence of different species is favored. If the key species fails, one species often prevails as a result of the increased competition between the prey animals and displaces the less competitive species, which leads to a decline in biodiversity in this community.

Word origin

The role that a keystone species plays in its ecosystem corresponds to that of a keystone in a round arch. Although the keystone is under the slightest pressure of all stones, the arch will still collapse without it. Likewise, an ecosystem can experience a dramatic shift if a key species is removed, although it has only played a minor role in terms of biomass content or productivity.

history

The concept of the key species was coined in 1969 by zoologist Robert T. Paine , a professor at the University of Washington , to explain the relationship between the starfish species Pisaster ochraceus and the mussel species Mytilus californianus . In his 1966 publication he described such a system in Makah Bay (Washington) and in another publication in 1969 he proposed the concept of key species. However, key species had been described long before, such as the Mauritius palm , the tree of life in the dry Llanos of Venezuela by Alexander von Humboldt .

Concepts

The interest in the preservation of biodiversity goes back a long time, but it wasn't until the 1980s that the term “biological diversity” emerged, later shortened to “biodiversity”. In 1992 in Rio de Janeiro at the United Nations Conference on Environment and Development (UNCED) the Convention on Biological Diversity was negotiated. The question arises, however, whether the conservation of all species, some of which are quite similar, is necessary to maintain the function of biodiversity and how much the loss of a species affects an ecosystem.

The following hypotheses were formulated for this purpose:

  • The equally important species hypothesis; Vitousek and Hooper, 1993) states that all species contribute equally to the function of an ecosystem and are therefore equally important. Accordingly, an increase in species would be proportional to an increase in function (e.g. increased primary production or stability).
  • The species redundancy hypothesis (Walker, 1992) states that, due to their similarity, some species can be dispensed with in an ecosystem. As the number of species increases, the function of an ecosystem initially increases sharply, but soon reaches saturation. It may also be that some keystone species are of particular importance.
  • The idiosyncratic hypothesis (Lawton 1994) states that there is no direct relationship between the number of species and function. However, species are not insignificant; rather, the number of species alone is not meaningful, but the species composition.

It is difficult to give preference to one of the hypotheses, since the meaning of a species only becomes apparent when it disappears in the respective system. Since this is often irreversible, it can be assumed that all types are important. According to the insurance hypothesis (Yachi and Loreau, 1999), redundancy in an ecosystem is not superfluous, but serves as a buffer for change.

Schwartz et al. a. investigated the relationship between species richness and function. When analyzing 40 different experiments, they found large differences. If the number of species is low, the function initially increases, and then changes to saturation. In contrast, there are only a few studies with a linear relationship between the number of species and function.

Examples

starfish

The example from the history of the term ( see above ) is the predatory starfish Pisaster ochraceus who performs this function on a rocky coast in the intertidal zone. It feeds this by various species of molluscs ( chitons , limpets , mussels ) and crustaceans ( barnacles and goose barnacles ). If the starfish is removed from the system, the Californian mussel ( Mytilus californianus ) displaces the remaining species. The California mussel is extremely successful in the competition for space and can form massive mussel beds in which biodiversity is reduced.

wolf

In Yellowstone National Park , the newly settled wolves were found to be a key species. They ensured an ecological balance in the park within a very short time. They reduced the number of elk that had previously grazed the park and destroyed the river banks. The wolves kept them off the river banks and no longer let them nibble on the trees. For the first time in years, trees could grow on the banks of the rivers. As a result, beavers settled in the park again . Now they found enough wood on the river banks to build their dams and castles. Due to the dams, the flow speed of the rivers decreased. Less earth was torn away, the erosion almost came to a standstill, the water became cleaner and the biodiversity in the water increased extremely. There were tons of insects and amphibians . This in turn attracted water birds of all kinds. In addition, there was now a large number of fish in the rivers again. The bears fed on these fish. However, the bears also ate much more frequently on the wolves' prey. They fought with the wolves for meat and took their prey from them. As a result, the number of bears rose sharply again. The number of fork jacks also recovered. They had previously been troubled by the coyotes without the wolves . The coyotes often ate the fawns and thus kept the number of pronghorns low. The wolves did not tolerate coyotes in their territory, but neither did they hunt the fawns of the pronghorns. They were far too small to be prey. As a result, the number of coyotes decreased and the number of pronghorns increased. At the same time there were many more ground-nesters in the park because the coyotes could no longer plunder the nests. The number of foxes also rose again. They were able to calmly catch mice again without the competition of the coyotes. There was undergrowth again and trees were growing again all over the park. The number of trees increased five times. Birds that built their nests in the undergrowth found a breeding place again. As a result, the number of birds of prey rose again. They found enough prey among the birds again.

Sea otters

Sea otters feed in large part on sea urchins, which in turn feed on seaweed . If sea otters are exterminated in a region, the sea urchins multiply so rapidly that they almost completely destroy the stocks of seaweed. Without the seaweed, many fish stocks collapse because the juvenile fish hide between the leaves of the seaweed. If sea urchins have destroyed the seaweed in a region, the habitat can regain its ecological balance very quickly as soon as sea otters immigrate to this area.

gnu

Although wildebeest are not predators, they are also key species. Their influence is much greater than that of most other animal species in their habitat. They keep the grass in the Serengeti short and prevent fires. Because young trees fall victim to fire particularly easily, the number of trees increases significantly when there are fewer fires. This in turn increases the number of giraffes and elephants . Beetles and other insects feed on the droppings of the many herbivores, which in turn serve as food for many birds. Many birds of prey feed on the birds, but also other predators such as the caracal . Even lions and leopards benefit from great wildebeest. The biodiversity increases enormously due to the higher number of wildebeest. If the wildebeest population decreases, the biodiversity also decreases significantly.

Sharks

Arbitrary overfishing of all species ruins the fishing grounds in the long run. Even so, the food chain in these fishing grounds remains intact for a long time. On the other hand, selective fishing , especially of predatory fish, is fatal. If you just catch the sharks and remove them as a key species from the ecosystem, the smaller hunters will lack the enemy. They can suddenly multiply strongly and subsequently prey on the fish that feed on plankton . Without plankton eaters, however, the plankton will increase excessively. Whole coral reefs then suffocate under rotting mountains of algae. In the end, a completely new ecosystem is formed with much shorter food chains and less biodiversity.

literature

  • Hermann Linder, Ulrich Kull: Lindner biology. Braunschweig 2005, ISBN 3-507-10930-1 .
  • Robert T. Paine : A Conversation on Refining the Concept of Keystone Species. In: Conservation Biology. Volume 9, Issue 4, 1995, pp. 962-964, doi: 10.1046 / j.1523-1739.1995.09040962.x
  • Federal Ministry of Agriculture, Forestry, Environment and Water Management: Green Series of the Ministry of Life, Volume 22: How many species do humans need? Searching for traces , pp. 23-24, ISBN 978-3-205-78516-3 .

Individual evidence

  1. ^ RT Paine: A Conversation on Refining the Concept of Keystone Species . In: Conservation Biology . tape 9 , no. 4 , 1995, p. 962-964 , doi : 10.1046 / j.1523-1739.1995.09040962.x .
  2. ^ Keystone Species Hypothesis. (No longer available online.) University of Washington, archived from the original January 10, 2011 ; Retrieved February 3, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.washington.edu
  3. ^ William Stolzenberg: Where the Wild Things Were: Life, death and ecological wreckage in a land of vanishing predators . Bloomsbury USA , 2008, ISBN 978-1-59691-299-1 .
  4. ^ RT Paine: Food Web Complexity and Species Diversity . In: The American Naturalist . tape 100 , no. 910 , 1966, pp. 65-75 , doi : 10.1086 / 282400 .
  5. ^ RT Paine: A Note on Trophic Complexity and Community Stability . In: The American Naturalist . tape 103 , no. 929 , 1969, p. 91-93 , doi : 10.1086 / 282586 .
  6. ↑ Andrea Wulf: Alexander von Humboldt and the invention of nature. Penguin, 2018, p. 104.
  7. ↑ Wolfgang Nentwig , Sven Bacher, Roland Brandl: Ecology compact. Spectrum Akademischer Verlag, Heidelberg 2007, ISBN 978-3-8274-1876-0 (Bachelor). P. 199ff.
  8. ↑ John W. laundre, Lucina Hernandez, Kelly B. Altendorf (2001): Wolves, elk, and bison: reestablishing the "landscape of fear" in Yellowstone National Park, USA Canadian Journal of Zoology 79 (8): 1401-1409. doi: 10.1139 / z01-094
  9. ↑ Cristina Eisenberg, S. Trent Seager, David E. Hibbs (2013): Wolf, elk, and aspen food web relationships: Context and complexity. Forest Ecology and Management 299: 70-80. doi: 10.1016 / j.foreco.2013.01.014 .
  10. ↑ Unlike Dolphins, Sea Otters That Use Tools Are Not Closely Related. On: smithsonianmag.com of March 30, 2017
    Why otters are the smartest craftsmen in the animal kingdom. On: stern.de from March 30, 2017