Showing papers by "Andy Hector published in 2001"

Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges

Abstract: The ecological consequences of biodiversity loss have aroused considerable interest and controversy during the past decade. Major advances have been made in describing the relationship between species diversity and ecosystem processes, in identifying functionally important species, and in revealing underlying mechanisms. There is, however, uncertainty as to how results obtained in recent experiments scale up to landscape and regional levels and generalize across ecosystem types and processes. Larger numbers of species are probably needed to reduce temporal variability in ecosystem processes in changing environments. A major future challenge is to determine how biodiversity dynamics, ecosystem processes, and abiotic factors interact.

Partitioning selection and complementarity in biodiversity experiments

Abstract: The impact of biodiversity loss on the functioning of ecosystems and their ability to provide ecological services has become a central issue in ecology. Several experiments have provided evidence that reduced species diversity may impair ecosystem processes such as plant biomass production. The interpretation of these experiments, however, has been controversial because two types of mechanism may operate in combination. In the 'selection effect', dominance by species with particular traits affects ecosystem processes. In the 'complementarity effect', resource partitioning or positive interactions lead to increased total resource use. Here we present a new approach to separate the two effects on the basis of an additive partitioning analogous to the Price equation in evolutionary genetics. Applying this method to data from the pan-European BIODEPTH experiment reveals that the selection effect is zero on average and varies from negative to positive in different localities, depending on whether species with lower- or higher-than-average biomass dominate communities. In contrast, the complementarity effect is positive overall, supporting the hypothesis that plant diversity influences primary production in European grasslands through niche differentiation or facilitation.

Local adaptation enhances performance of common plant species

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.

Community diversity and invasion resistance: An experimental test in a grassland ecosystem and a review of comparable studies

Abstract: The relationship between community diversity and invasion resistance in a grassland was examined using experimental plant assemblages that varied in species richness and composition. The assemblages were weeded for three seasons to remove unsown species and we used the number of weeded seedlings, their total biomass and the number of species removed as indicators of community resistance and susceptibility to invasion. In general, we found a positive relationship between invasion resistance and increasing community diversity. Similar patterns of establishment were observed at the end of the fourth field season after several months without weeding. Increased invasion resistance with higher diversity appears to come through reduced levels of several above- and belowground resources, although these did not fully explain the effects of species richness in the study’s analyses. Experimental increases and reductions of litter biomass within the study’s experimental plant assemblages did not modify these patterns significantly. A review of comparable studies of invasion across directly manipulated diversity gradients revealed similar patterns. Positive effects of species diversity on invasion resistance were found in experimental manipulations of plant diversity conducted in the field and in the glasshouse, from studies with aquatic microcosms and in a marine system. Although some exceptions to this pattern were found in both terrestrial plant systems and aquatic microcosms, it was concluded that in biodiversity manipulation experiments more diverse communities are generally more resistant to invasion.

Conservation implications of the link between biodiversity and ecosystem functioning

Abstract: The relationship between biodiversity and individual ecosystem processes is often asymptotic, saturating at relatively low levels, with some species contributing more strongly than others. This has cast doubt on arguments for conservation based on maintenance of the functioning of ecosystems. However, we argue that the link between biodiversity and ecosystem functioning is an important additional argument for conservation for several reasons. (1) Although species differ in importance to ecosystem processes, we do not believe that this argues for preservation of just a few species for two reasons: first, it is nearly impossible to identify all species important to the numerous systems and processes on which humans depend; second, the important species themselves may depend on an unknown number of other species in their communities. (2) Arguments for conservation based on ecosystem functioning are complementary to other utilitarian, ethical and aesthetic justifications. No single reason will convince all people or protect all species, however the combination produces a strong case for conservation of biodiversity. (3) Even if the relationship between biodiversity and ecosystem functioning is asymptotic at local spatial scales and in the short term, effects of biodiversity loss are likely to be important at larger temporal and spatial scales. (4) Initial arguments for the importance of biodiversity for ecosystem functioning were largely based on a precautionary approach (points 1-3). However, we are now moving to a scientific position based on accumulating experimental evidence. The future challenge is the integration of this scientific research with policy.

Erratum: Partitioning selection and complementarity in biodiversity experiments

Abstract: Nature, 412, 72–76 (2001). In Figures 2 and 3, some regression lines were very faint or missing. The corrected panels are reproduced below. All panels in both figures should also have shown the null hypothesis as a horizontal dashed line through zero.

The functioning of European grassland ecosystems : potential benefits of biodiversity to agriculture

Abstract: About half the farmland of Europe is grassland pasture or hay meadow, and much is impoverished in plant species due to the addition of fertilizers and pesticides, agricultural re-sowing, habitat fragmentation, land abandonment and changes in grazing and mowing regimes. Given this widespread reduction, it is important to understand the effect that loss of biodiversity is having upon our wider environment. Here the authors summarize the main results from the BIODEPTH project, the first multinational, large-scale experiment to examine directly the relationship between plant diversity and the processes that determine the functioning of ecosystems. The results suggest that preserving and restoring grassland diversity may be beneficial to maintaining desirable levels of several ecosystem processes, and may therefore have applications in land management and agriculture.