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

The role of biodiversity in regulating the stability of ecosystem functioning (functional stability) 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 of functional response to its mean) in reaching conclusions. We argue that the use of CV for this purpose can lead to misleading conclusions on functional stability. We use illustrative scenarios to show that an assessment of functional 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. 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.