Functional trait metrics are sensitive to the completeness of the species' trait data?
Article first published online: 27 NOV 2013
© 2013 The Author. Methods in Ecology and Evolution © 2013 British Ecological Society
Methods in Ecology and Evolution
Volume 5, Issue 1, pages 9–15, January 2014
How to Cite
Pakeman, R. J. (2014), Functional trait metrics are sensitive to the completeness of the species' trait data?. Methods in Ecology and Evolution, 5: 9–15. doi: 10.1111/2041-210X.12136
- Issue published online: 14 JAN 2014
- Article first published online: 27 NOV 2013
- Accepted manuscript online: 28 OCT 2013 12:15PM EST
- Manuscript Accepted: 18 OCT 2013
- Manuscript Received: 20 JUN 2013
- Scottish Government's Rural and Environment Science and Analytical Services Division
- functional dispersion;
- functional divergence;
- functional evenness;
- functional richness;
- plant functional traits;
- Rao's entropy;
- trait sampling
- Functional diversity (FD) is an important concept for studies of both ecosystem processes and community assembly, so it is important to understand the behaviour of common metrics used to express it.
- Data from an existing study of the relationship between FD and environmental drivers were used to simulate the impact of a progressive failure to measure the traits of all the species present under three scenarios: intraspecific variation between sites ignored (i), assessed (ii) or (iii) ignored but with metrics calculated at the sampling unit rather than the site level.
- All the FD metrics were highly sensitive to failing to measure the traits of all the species present. Functional dispersion, functional richness and Rao's entropy all generally declined with a reduced proportion of species or cover assessed for traits, whilst functional divergence and evenness increased for some sites and decreased for others. Functional richness was the most sensitive (mean absolute deviation at 70% of species assessed had a range of 11·2–28·2% across scenarios), followed by functional evenness (range 6·4–38·5%), functional divergence (5·2–8·3%), Rao's entropy (1·4–7·0%) and functional dispersion (0·7–3·5%).
- It is clear that failing to measure the traits of all species at a site can have a serious impact on the value of any functional trait metric computed and on any conclusions drawn from such data. Future studies of FD need to concentrate on the potential impact of the sampling regime of both traits and species and the scale at which the computations are made on the behaviour of metrics and subsequent robustness of the results.