Poesch, M.S. (2015) To dendrogram or not? Consensus methods show that the question needed to move functional diversity metrics forward. Ideas in Ecology and Evolution. 8: 70-74.

Abstract:

Functional diversity indices have become important tools for measuring variation in species characteristics that are relevant for ecosystem services. A frequently used dendrogram-based method for measuring functional diversity, ‘FD’, was shown to be sensitive to methodological choices in its calculation, and consensus methods have been suggested as an improvement. The objective of this study was to determine whether consensus methods can be used to reduce sensitivity when measuring FD. To calculate FD, a distance measure and a clustering method must be chosen. Using data from three natural communities, this study demonstrates that consensus methods were unable to resolve even simple choices of distance measure (Euclidean and cosine) and clustering method (UPGMA, complete and single linkage). Overall, there was low consensus, ranging from 41–45%, across choices inherent in functional diversity. Further, regardless of how FD was measured, or how many species were removed from the community, FD closely mirrored species richness. Future research on the impact of methodological choices, including choices inherent in producing a dendrogram and the statistical complications they produce, are needed to move functional diversity metrics forward.

Citation: Poesch, M.S. 2015. To dendrogram or not? Consensus methods show that the question needed to move functional diversity metrics forward. Ideas in Ecology and Evolution. 8: 70-74.

Also Read:

Serbu, J. A., St. Louis, V. L., Emmerton, C. A., Tank S., Criscitello, A., Silins, U., Bhatia, M., Cavaco, M., Christenson, C., Cooke, C., Drapeau, H., Enns, S. J., Flett, J., Holland, K., Lavelle-Whiffen, J., Ma, M., Muir, C., Poesch, M. S., and J. Shin. (2023). A comprehensive biogeochemical assessment of climate-threatened glacial river headwaters on the eastern slopes of the Canadian Rocky Mountains. JGR Biogeosciences.

Poesch, M.S., Walker, S.C., and D.A. Jackson (2009) Functional diversity indices can be driven by methodological choices and species richness. Ecology 90(2): 341-346.

Abstract:

Functional diversity is an important concept in community ecology because it captures information on functional traits absent in measures of species diversity. One popular method of measuring functional diversity is the dendrogram-based method, FD. To calculate FD, a variety of methodological choices are required, and it has been debated about whether biological conclusions are sensitive to such choices. We studied the probability that conclusions regarding FD were sensitive, and that patterns in sensitivity were related to alpha and beta components of species richness. We developed a randomization procedure that iteratively calculated FD by assigning species into two assemblages and calculating the probability that the community with higher FD varied across methods. We found evidence of sensitivity in all five communities we examined, ranging from a probability of sensitivity of 0 (no sensitivity) to 0.976 (almost completely sensitive). Variations in these probabilities were driven by differences in alpha diversity between assemblages and not by beta diversity. Importantly, FD was most sensitive when it was most useful (i.e., when differences in alpha diversity were low). We demonstrate that trends in functional-diversity analyses can be largely driven by methodological choices or species richness, rather than functional trait information alone.

Citation: Poesch, M.S., Walker, S.C., and Jackson, D.A. 2009. Functional diversity indices can be driven by methodological choices and species richness. Ecology 90(2): 341-346.

Also Read:

Theis, S.*, Ruppert, J.*, Shirton, J.* and M.S. Poesch (2022) Measuring beta diversity components and beneficial effects of coarse woody habitat introduction on invertebrate and macrophyte communities in a shallow northern boreal lake: implications for offsetting. Aquatic Ecology 56: 793-814.

Walker, S., Poesch, M.S. and D. A. Jackson. (2008) Functional rarefaction: Estimated functional diversity from field data. Oikos 117(2): 286-296.

Abstract:

Studies in biodiversity-ecosystem function and conservation biology have led to the development of diversity indices that take species’ functional differences into account. We identify two broad classes of indices: those that monotonically increase with species richness (MSR indices) and those that weight the contribution of each species by abundance or occurrence (weighted indices). We argue that weighted indices are easier to estimate without bias but tend to ignore information provided by rare species. Conversely, MSR indices fully incorporate information provided by rare species but are nearly always underestimated when communities are not exhaustively surveyed. This is because of the well-studied fact that additional sampling of a community may reveal previously undiscovered species. We use the rarefaction technique from species richness studies to address sample-size-induced bias when estimating functional diversity indices. Rarefaction transforms any given MSR index into a family of unbiased weighted indices, each with a different level of sensitivity to rare species. Thus rarefaction simultaneously solves the problem of bias and the problem of sensitivity to rare species. We present formulae and algorithms for conducting a functional rarefaction analysis of the two most widely cited MSR indices: functional attribute diversity (FAD) and Petchey and Gaston’s functional diversity (FD). These formulae also demonstrate a relationship between three seemingly unrelated functional diversity indices: FAD, FD and Rao’s quadratic entropy. Statistical theory is also provided in order to prove that all desirable statistical properties of species richness rarefaction are preserved for functional rarefaction.

Citation: Walker, S., Poesch, M.S. and Jackson, D.A. 2008. Functional rarefaction: Estimated functional diversity from field data. Oikos 117(2): 286-296.

Also Read:

Banting, A.*, Vinebrooke, R., Taylor, M., Carli, C. and M.S. Poesch. (2021) Impacts of a regionally-native predator on littoral macrobenthos in fishless mountain lakes: implications for assisted colonization. Conservation Science and Practice 3(2): e344.