Biodiversity has been, for a long time, an important subject of study in ecology. Beyond science, however, biodiversity gained interest with the general public after the Biodiversity Summit in Rio in 1992 where the ownership of national genetic resources was regulated (WBGU 2000). People from all walks of life, including politicians, became aware of the loss of species, a loss caused by human influences being a thousandfold greater than natural rates of extinction. Scientists recognised that knowledge of biodiversity and topics linked to it was rather modest and feared that numerous organisms would become extinct without ever having been even scientifically recorded (Mooney et al. 1996).

Steady-state theory in island biogeography

In vegetation ecology relationships between the size of an area and the number of living plant species are sought. Initially, islands were chosen for study with investigation of how they were colonised and how the number of species was determined. Understanding that developed from characterisation of an area and the species on it developed into the steady-state theory of island biogeography. This underlines the importance of stepping stones for the colonisation and is based on the idea that, over long periods of time, colonisation and extinction rates are in equilibrium. The number of species is determined by the size of the island and the distance from sources of diaspores of potential colonists, as well as the diversity of habitats which determines survival.

The theory of island biogeography was criticised mostly because the competitive relationships between species were not taken into account. Despite this, this theory is used in mainland "island" biogeography. It is the basis of biotope organisation and is used in determination of the minimum size for maintenance of habitats in nature conservation. Anthropogenic influences are present in almost all habitats, and the consequent disturbance of the environment, make it increasingly difficult to determine rules characterising areas. Currently, it is considered that the processes are less and less deterministic and are becoming increasingly stochastic.

Mere numbers of species were not regarded sufficient to understand communities in their habitats. Plants and animals were not only to be regarded as resources, but as decisive influences on processes in ecosystems (see Chap. 3). Clearly biodiversity developed through evolutionary processes by adaptation to abiotic conditions in areas with already established competitors. Why some plants form communities with few species and other with many species, what regulates the composition of species and how this influences ecosystem processes was - and still is - unknown.

At the moment ecosystems are increasingly disturbed by man and habitats are lost, whilst new sites are developed by human interference; man is responsible for the previously unknown diversity in traditional agricultural landscapes of central Europe and, therefore, it is very urgent to clarify important questions on development, loss and function of biodiversity.

A short examination of the present knowledge of the status of species will be followed by an examination of the origins of research on biodiversity based on the work of Whittaker. Questions about the hierarchy, and temporal and spatial dimensions of biodiversity will be central. Finally, functional aspects of biodiversity of bio-cenoses and ecosystems will be discussed (see Chap. 3) and questions related to loss of biodiversity discussed in relation to problems of environmental protection.

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