[show abstract][hide abstract] ABSTRACT: Insurance effects of biodiversity can stabilize the functioning of multispecies ecosystems against environmental variability when differential species' responses lead to asynchronous population dynamics. When responses are not perfectly positively correlated, declines in some populations are compensated by increases in others, smoothing variability in ecosystem productivity. This variance reduction effect of biodiversity is analogous to the risk-spreading benefits of diverse investment portfolios in financial markets. We use data from the BIODEPTH network of grassland biodiversity experiments to perform a general test for stabilizing effects of plant diversity on the temporal variability of individual species, functional groups, and aggregate communities. We tested three potential mechanisms: reduction of temporal variability through population asynchrony; enhancement of long-term average performance through positive selection effects; and increases in the temporal mean due to overyielding. Our results support a stabilizing effect of diversity on the temporal variability of grassland aboveground annual net primary production through two mechanisms. Two-species communities with greater population asynchrony were more stable in their average production over time due to compensatory fluctuations. Overyielding also stabilized productivity by increasing levels of average biomass production relative to temporal variability. However, there was no evidence for a performance-enhancing effect on the temporal mean through positive selection effects. In combination with previous work, our results suggest that stabilizing effects of diversity on community productivity through population asynchrony and overyielding appear to be general in grassland ecosystems.
[show abstract][hide abstract] ABSTRACT: Biodiversity and ecosystem functioning research has been some of the most controversial of the last decade but rapid progress has been made by deriving hypotheses from the differing view points and challenging them with appropriate experimental and analytical tests (Loreau et al. 2001). Here we address some recent criticisms of the BIODEPTH project (Thompson et al. 2005) and show that: 1. While legume species play an important role in the BIODEPTH results, patterns are not generally consistent with the multispecies sampling effect for legumes proposed by Huston & McBride (2002) as suggested in Thompson et al. (2005). 2. The BIODEPTH results are also not consistent with transient biodiversity effects. Levels of species diversity were generally maintained over the 3 years of the project (i.e. little competitive exclusion) and diversity-productivity relationships in BIODEPTH generally strengthened during the experiments.
[show abstract][hide abstract] ABSTRACT: We present a multisite analysis of the relationship between plant diversity and ecosystem functioning within the European BIODEPTH network of plant-diversity manipulation experiments. We report results of the analysis of 11 variables addressing several aspects of key ecosystem processes like biomass production, resource use (space, light, and nitrogen), and decomposition, measured across three years in plots of varying plant species richness at eight different European grassland field sites. Differences among sites explained substantial and significant amounts of the variation of most of the ecosystem processes examined. However, against this background of geographic variation, all the aspects of plant diversity and composition we examined (i.e., both numbers and types of species and functional groups) produced significant, mostly positive impacts on ecosystem processes.
Analyses using the additive partitioning method revealed that complementarity effects (greater net yields than predicted from monocultures due to resource partitioning, positive interactions, etc.) were stronger and more consistent than selection effects (the covariance between monoculture yield and change in yield in mixtures) caused by dominance of species with particular traits. In general, communities with a higher diversity of species and functional groups were more productive and utilized resources more completely by intercepting more light, taking up more nitrogen, and occupying more of the available space. Diversity had significant effects through both increased vegetation cover and greater nitrogen retention by plants when this resource was more abundant through N2 fixation by legumes. However, additional positive diversity effects remained even after controlling for differences in vegetation cover and for the presence of legumes in communities. Diversity effects were stronger on above- than belowground processes. In particular, clear diversity effects on decomposition were only observed at one of the eight sites.
The ecosystem effects of plant diversity also varied between sites and years. In general, diversity effects were lowest in the first year and stronger later in the experiment, indicating that they were not transitional due to community establishment. These analyses of our complete ecosystem process data set largely reinforce our previous results, and those from comparable biodiversity experiments, and extend the generality of diversity–ecosystem functioning relationships to multiple sites, years, and processes.
Read More: http://www.esajournals.org/doi/abs/10.1890/03-4101
[show abstract][hide abstract] ABSTRACT: Geographic variation can lead to the evolution of different local varieties, even in widespread forage plants. We investigated the performance of common forage plants in relation to their genetic diversity and local adaptation at a continental scale using reciprocal transplants at eight field sites across Europe over a 2-year period. The overall performance of the three test species, Trifolium pratense, Dactylis glomerata, Plantago lanceolata, was generally highest for plants replanted at their home site and declined with increasing transplanting distance. The three species differed in the fitness components responsible for the increased overall performance and selection advantage at home sites. In addition to the effects of local adaptation, the majority of measured traits in all three species also showed ecotypic variation. However, no single ecotype of any species was able to outperform the locally adapted strains and do best at all sites, highlighting the importance of maintaining these plant genetic resources.
[show abstract][hide abstract] ABSTRACT: At eight European field sites, the impact of loss of plant diversity on primary productivity was simulated by synthesizing
grassland communities with different numbers of plant species. Results differed in detail at each location, but there was
an overall log-linear reduction of average aboveground biomass with loss of species. For a given number of species, communities
with fewer functional groups were less productive. These diversity effects occurred along with differences associated with
species composition and geographic location. Niche complementarity and positive species interactions appear to play a role in generating diversity-productivity relationships
within sites in addition to sampling from the species pool.
[show abstract][hide abstract] ABSTRACT: At eight European field sites, the impact of loss of plant diversity on primary productivity was simulated by synthesizing grassland communities with dif-ferent numbers of plant species. Results differed in detail at each location, but there was an overall log-linear reduction of average aboveground biomass with loss of species. For a given number of species, communities with fewer func-tional groups were less productive. These diversity effects occurred along with differences associated with species composition and geographic location. Niche complementarity and positive species interactions appear to play a role in generating diversity-productivity relationships within sites in addition to sam-pling from the species pool. Because species differ in their ecological at-tributes, the loss of biodiversity from local communities may be detrimental to the eco-system goods and services on which humans ultimately depend (1). This issue has been the subject of major recent research efforts using experimental plant assemblages (2–6). How-ever, differences in aims and approaches, and the fact that experimental manipulations of diversity have been restricted to single local-ities, limit the ability of ecologists to make generalizations and predictions. The design, analysis, and interpretation of these experi-ments are also complex (7), and the view that the loss of plant species can be detrimental to ecosystem functioning remains contentious (8–11). In particular, the mechanisms under-lying the relationship between species rich-ness and ecosystem functioning are still the subject of debate because of the difficulty in identifying and interpreting the importance of niche complementarity versus "sampling ef-fects" (8, 12, 13). Here we report patterns of aboveground plant biomass from the most extensive experiment to date in terrestrial ecosystems, and we examine the underlying mechanisms. We used standardized protocols to estab-lish experimental assemblages of grassland species (grasses and forbs) that varied in species richness, and we measured above-ground plant biomass production at two locali-ties in the United Kingdom and at single sites in Germany, Ireland, Greece, Portugal, Sweden, and Switzerland (14, 15). Sites differed widely