Biodiversity experiments — artificial constructions or heuristic tools?

Abstract

Biodiversity experiments are important tools for basic research. Here, we discuss their scientific basis, some major hypotheses and review the most prominent results according to the role of biodiversity in productivity, invasion and nutrient cycling. Progress in methods and insights is documented. Shortcomings and restrictions of recent approaches are identified. Finally, we point out research perspectives. At the global level, the loss of rare species is recorded. Regional extinctions of populations are also documented. Communities are becoming more and more uniform due to standardized management techniques and increased dispersal of ruderal species. Alien and invasive species are contributing at the regional scale to an increase in species diversity whereas rare species may be lost from the same area. Changes of biodiversity have many facets at different scales. The mechanisms that are responsible for the ongoing changes are generally being identified, with rapid land use changes being the most prominent (Sala et al. 2000). Early biodiversity research concentrated on the detection and description of taxa and their diversity within certain ecosystems or regions and on their loss or decline (e.g. Ehrlich and Ehrlich 1981). Due to the complexity of natural and anthropogenic ecosystems and landscapes, monitoring of such changes is rather time consuming and will deliver sound results only for selected case studies and areas. Science has to analyse the mechanisms of change and to contribute to coping strategies through predictive conclusions. The long-term preservation of sound ecosystems is needed. Strategies that consider biodiversity and ecosystem functioning are requested (Schwartz et al. 2000; Hector et al. 2001b). One category that adds complexity to the system is the interaction between biotic compartments, and between biotic and abiotic compartments differing from stand to stand. As early as in the 1920s the recognition of this fact lead to the development of the individualistic concept by Gleason