Abstract
Grasslands deliver the resources for food production and are among the most biologically diverse ecosystems. These characteristics are often in conflict as increasing yield through fertilization can lead to biodiversity loss. Thus, the challenge in grassland management is to sustain both yield and diversity. Biodiversity–ecosystem functioning experiments typically reveal a positive relationship between manipulated species diversity and productivity. In contrast, observations of the effect of increasing productivity via fertilization suggest a negative association with biodiversity. Using a mathematical model simulating species co-existence along a resource gradient, we show that trade-offs and species pool structure (size and trait distribution) determines the shape of the productivity-diversity relationship. At a constant resource level, over-yielding drives a positive relationship between biodiversity and productivity. In contrast, along a resource gradient, the shape of the productivity-diversity relationship is determined by the distribution of species along trade-off axes and often resulted in a bell-shaped relationship. In accordance to this theoretical result, we then explain the general trend of plant biodiversity loss with fertilisation in the European flora, by showing empirical evidence that trait distribution of plant species pools throughout Europe is biased toward species preferring poorer soils.
Highlights
Grasslands provide a wealth of ecosystem services to human society, supported by species diversity and functions[1]
We show with a mathematical model that the link between the trait distribution within the species pool and the realized community determines the response to resource gradients, and unifies experimental observations and empirical observations
Along a resource gradient, the shape of the relationship between diversity and productivity varies according to the trait distribution within the species pool
Summary
Grasslands provide a wealth of ecosystem services to human society, supported by species diversity and functions[1]. Greater niche similarity between conspecifics leads to greater intra- than inter-specific competition, and so for a similar number of individuals, there is less competitive interference between individuals in a diverse community compared to a low-diversity community leading to a higher productivity These alternative mechanisms provide distinct expectations for the shape of the biodiversity–productivity relationship and should be studied within a unified model. We present a plant–resource model that provides theoretical expectations about the causes of the shape of productivity-diversity relationships Using this model, we show (1) that trade-offs among species traits are necessary conditions for the emergence of niche partitioning along a productivity gradient and a non-positive relationship between diversity and productivity, and (2) how the structure of the species pool affects productivity–diversity relationships. The model links the quantity of a single resource, R, representing soil resources, to the biomass, Pi, of plant species i in a pool of N species with the following architecture: dR dt
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