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.

Phylogenetic constraints on ecosystem functioning

“…2). Note that our analysis assumes the most productive lineage excludes all others by competition, as it does not account for the relative abun dance of the lineages at the end of the experiment, and consequently is not a true measurement of the sampling effect 22 . There was almost no overyielding for all mixtures (a majority of assemblages had a negative overyielding index).…”

Across species‐pool aggregation alters grassland productivity and diversity

“…Plot Simpson's diversity ( D ) was calculated as $D=1/({\sum }_{i=1}^s{p}_i^2)$, where S is the number of species in the community and p i is the proportional biomass of species i . Selection and complementarity effects were calculated using the additive‐partitioning model of Loreau and Hector (2001) based on species mixture and monoculture biomass production. This was based on species proportions by individuals (number of individuals of species i /64 individuals) at planting for year one and previous year proportion of plot biomass for each species in years two and three.…”

“…Soil surface light and volumetric soil moisture were similarly compared across sample dates within each growing season. Plot biomass, Simpson's Diversity, and soil moisture were natural log transformed, percent PAR was arcsine square root transformed, and selection and complementarity were square root transformed with the original sign maintained (Loreau and Hector 2001) to meet assumptions. Significant ANOVA tests were followed by least significant difference tests to identify differences among treatment groups.…”

Understanding and monitoring the consequences of human impacts on intraspecific variation

“…Two primary mechanisms can explain the positive relationship between diversity (both among and within species) and various community/ecosystem processes (Loreau & Hector, 2001). First, diverse communities use a wider range of resources due to resource partitioning or positive species interactions (i.e., “complementarity effects”), which can increase productivity and nutrient cycling.…”