Keystone species

As a keystone species (based on the engl. Term " Keystone Species" ) a kind referred to in ecology, which exerts a disproportionate influence on the species diversity of a community in comparison to their low frequency. Even if key species may occur on each trophic level, there are usually predators. Due to the grazing pressure of the keystone, the population density among the prey is so far reduced that the competition between the prey species decreases and the coexistence of different species is favored. Turns out the key type, continuing as a result of increased competition between the prey often a kind through and displaces the weaker competitive species, which leads to a reduction in biodiversity in this community.

Word origin

The role of a keystone (English keystone species) in their ecosystem, corresponds to a key stone (English keystone ) in a round arch. Although the keystone of all stones is under the slightest pressure, breaking the bow without it together yet. Similarly, an ecosystem will experience a dramatic shift if a keystone species is removed, even though this has in terms of proportion of biomass or productivity, played only a small role.

History

The concept of keystone species in 1969 by the zoologist Robert T. Paine, a professor emeritus at the University of Washington, coined to explain the relationship between the starfish Pisaster ochraceus (s) of mussel Mytilus californianus, and the ( en ). In its release in 1966, he described such a system in Makah Bay ( Washington) and suggested in a further publication in 1969, the concept of key species.

Concepts

The interest in preservation of biodiversity already dates back a long time, but only in the 1980s, the term "Biological diversity", later shortened " biodiversity " was born. In 1992, in Rio de Janeiro on the United Nations Conference on Environment and Development (UNCED ), the Convention on Biological Diversity ( english Convention on Biological Diversity ) negotiated. However, it raises the question of whether the conservation of all, sometimes quite similar species to safeguard the function of biodiversity is needed and how much the loss of a species affects ecosystem.

To this end, the following hypotheses were formulated:

• The equivalence of - the -species hypothesis (English Equally important species hypothesis, Vitousek and Hooper, 1993) states that all species contribute equally to the function of an ecosystem and thus are equally important. Accordingly, an increase in species in proportion to an increase in function ( eg, increased primary production or stability) would behave.

• The redundant species hypothesis ( engl. species redundancy hypothesis; Walker, 1992) states that due to their similarity, some species are dispensable for an ecosystem. Thus, the function of an ecosystem initially increases sharply, but soon reaches a saturation. It may also be that some key species (English keystone species) are of particular importance.

• The idiosyncrasy hypothesis ( engl. idiosyncratic hypothesis; Lawton 1994) states that there is no direct relationship between species number and function. However, species are not without importance, but rather the number of species is not only meaningful, but the species composition.

It is difficult to choose one of the hypotheses to be suitable, as the meaning of a type apparently only with her ​​disappearance is. For safety, one should therefore assume that all species are important. According to the insurance hypothesis (german insurance hypothesis; Yachi and Loreau, 1999) is redundancy in an ecosystem also not superfluous, but serves as a buffer for changes.

Schwartz et al found in an analysis of 40 different experiments (2000), which were carried out in recent years to find out a relationship between species richness and function, note that the results are very different. However, it usually finds a relationship between species number and function at a low number of species and a subsequent saturation. The are only a few studies with a linear relationship between species number and function against.

Examples

A classic example is the predatory starfish Pisaster ochraceus has exercised this function on a rocky coast in the intertidal zone. It feeds itself on its different species of molluscs ( chitons, limpets, mussels ) and crustaceans ( barnacles and goose barnacles). If the starfish removed from the system, replaced the California mussel (Mytilus californianus ) the remaining species and biodiversity decreases. The California mussel has been extremely successful in the competition for space and can form massive mussel beds.

Robert T. Paine described the scenario given above in the Mukkaw Bay in Washington (State) and introduced the concept of keystone species (English keystone species) in 1969.