Many different aspects of biodiversity (e.g. taxonomic diversity, genetic diversity) can be monitored in an ecosystem and each of these aspects has the potential to provide a unique answer to environmental change. However most monitoring programs traditionally estimate biodiversity only considering a single taxonomic approach while functional dimensionality is generally neglected. The paper of Vandewalle et al. (2010) shows that the use of functional traits for biodiversity monitoring clearly complements taxonomic indicators, bringing new insights for understanding ecological response to land use change. Another great point is that this paper focuses especially on functional traits of animal groups as biodiversity indicators, which is relatively uncommon. Animal traits have not been often used to access community response as much as plant traits have, and the authors present four case studies across different ecosystems and groups (benthic invertebrates, collembolans, insects and birds) suitably using their traits to access it. So, although I do recognize that this paper does not bring really novel concepts to ecological studies, it does help functional diversity studies to overcome certain barriers which have restrained the development of the field for the past years. The paper shows its applicability to applied studies, such as biodiversity monitoring, and a feasible methodological approach capable to understand diversity patterns.
The study cases presented in the paper focus on the response of biodiversity estimated by three components with simple metrics: species diversity (Simpson index), functional diversity (Rao index, e.g. the range of trait values within the community) and mean traits (calculated for each species trait). Results showed positive relations between functional and species diversity descriptors for different biological groups, but in some cases the functional and taxonomic dimensions responded to different drivers. For example, beetle species diversity was directly correlated with landscape heterogeneity while the functional dimension (both functional diversity and mean traits) was influenced by the shift in landscape composition from forested to open agricultural landscapes. For benthic invertebrates, the results imply that are the community mean trait values (e.g. such as those related to aquatic stages, reproduction and dispersion) that respond to environmental gradients rather than the overall community diversity. So, what makes this paper interesting for me is that it shows that without functional knowledge a biodiversity monitoring program may achieve different conclusions. This feasible and applicable sequence of monitoring indicators allowed the determination of changes in community structure.
Nevertheless I think that some other dimensions could be included as additional indicators of biodiversity. Dominant traits associated to functional diversity express the importance of the community mean traits and its variation, but does not express the convergence or divergence between communities, what could be assessed by beta functional diversity (see de Bello et al 2009). Additionally, I believe that functional diversity, as almost all community properties, should be calculated in different spatial and temporal scales.
de Bello, F; Thuiller, W.; Lepsˇ, J; Choler, P.; Clément, J.; Macek, P.; Sebastià, M. & Lavorel, S. 2009. Partitioning of functional diversity reveals the scale and extent of trait convergence and divergence. Journal of Vegetation Science 20:475-486. (http://onlinelibrary.wiley.com/store/10.1111/j.1654-1103.2009.01042.x/asset/j.1654-1103.2009.01042.x.pdf?v=1&t=h8ywv6l0&s=44c302d8cf56592c9a19e9f22d6388430c1c6555)