Assessing the relationship between biodiversity and stability of ecosystem function--is the coefficient of variation always the best metric?

Abstract

The role of biodiversity in regulating the stability of ecosystem functioning has importance for the reliable delivery of ecosystem services. To date, ecological studies that aim to measure stability in ecosystem function across a range in diversity have almost universally used the coefficient of variation (CV, the ratio of standard deviation (SD) of functional response to its mean), or its inverse 1/CV, in reaching conclus-ions. We argue that the use of CV for this purpose can lead to misleading conclusions on stability. We consider that defining the stability of ecosystem functioning solely in terms of the CV confines the term stability to a usage and context that is not natural or intuitive to many who wish to address questions about the reliability with which ecosystems deliver services. We use illustrative scenarios to show that an assessment of stability based on the CV is not as effective in many cases as one based on joint consideration of mean and standard deviation, and may be completely misleading, especially where low values of functional response are a desirable outcome. Faced with similar questions, agronomic studies that aim to assess the stability of ecosystem function (comparison of yield of different varieties within and across different sites) take both the average response and variability within-and between-sites into consideration. We argue that the way stability is measured should be appropriate for the questions about the delivery of ecosystem services that are being addressed. We suggest approaches based on the joint modelling of the mean and standard deviation as a basis for addressing questions of biodiversity and stability of ecosystem function. Assessment of the importance of diversity in providing ecosystem services for society is more likely to be made on socio-economic evaluation of trade-offs between mean and variability of the function rather than its stability as measured by the coefficient of variation.