Suchergebnisse

During the past decades a worldwide loss of biodiversity has been identified, and understanding the consequences for biotic interactions and associated ecosystem services has become a major focus. Ecosystem services of substantial importance are for example crop pollination, pest predation or parasitism. The Jena-Experiment, which is based on an experimental manipulation of plant species richness, offers a great opportunity to study the effects of plant diversity per se, because many confounding factors such as management or land-use intensity of descriptive field studies are excluded. We studied invasion success and performance of Centaurea jacea at different plant diversity levels. Further we focused on the effects of plant species richness, on flower visitors, trap-nesting Hymenoptera and plant-pollinator networks. The first part of the thesis describes the impact of plant species richness and plant functional group richness on the survival and performance on the transplanted phytometer species Centaurea jacea in two consecutive years. The survival of transplanted Centaurea jacea into an established plant community decreased with increasing richness of plant species and plant functional groups and in plots, where legume species were present ...

In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.