Goodness-of-fit measures of evenness: a new tool for exploring changes in community structure

Abstract

Abstract. Growing concern about the fate of biodiversity, highlighted by the Convention on Biological Diversity's 2010 and 2020 targets for stemming biodiversity loss, has intensified interest in methods of assessing change in ecological communities through time. Biodiversity is a multivariate concept, which cannot be well-represented by a single measure. However, diversity profiles summarize the multivariate nature of multi-species datasets, and allow a more nuanced interpretation of biodiversity trends than unitary metrics. Here we introduce a new approach to diversity profiling. Our method is based on the knowledge that an ecological community is never completely even and uses this departure from perfect evenness as a novel and insightful way of measuring diversity. We plot our measure of departure as a function of a free parameter, to generate ''evenness profiles''. These profiles allow us to separate changes due to dominant species from those due to rare species, and relate these patterns to shifts in overall diversity. This separation of the influence of dominance and rarity on overall diversity enables the user to uncover changes in diversity that would be masked in other methods. We discuss profiling techniques based on this parametric family, and explore its connections with existing diversity indices. Next, we evaluate our approach in terms of predicted community structure (following Tokeshi's niche models) and present an example assessing temporal trends in diversity of British farmland birds. We conclude that this method is an informative and tractable parametric approach for quantifying evenness. It provides novel insights into community structure, revealing the contributions of both rare and common species to biodiversity trends.Key words: biodiversity; divergence measures; diversity indices; diversity ordering; diversity profiles; evenness; goodness-of-fit statistics; Hill's diversity numbers; rare species; species abundance distribution.

Diversity and equitability ordering profiles applied to study forest structure

“…The Lorenz curve is another concept related to size ordering for characterizing equitability (Studeny et al, 2011). Even though the Lorenz curve was originally applied to a different problem area (inequality of economic income), it is equivalent to an intrinsic size diversity ordering method when richness is constant (Lambshead et al, 1983), as it is also based on accumulated dominance.…”

“…As explained, a measurement of diversity comprises both richness of size classes and the equitability of abundances among them (Studeny et al, 2011). There may be interest in studying the inequality among size classes independently from how many they are, i.e., the shape of the abundance vector.…”

The geometric mean of relative abundance indices: a biodiversity measure with a difference

“…Studeny et al (2011) address this insensitivity by embedding the Shannon and Simpson's indices in a parametric family of indices, where a parameter controls the relative weighting given to rare and common species in the community. This allows a trade-off between precision and sensitivity to changes amongst rarely-recorded species.…”

Using Species Proportions to Quantify Turnover in Biodiversity

“…Cressie and Read (1984) considered these two tests as special cases of power divergence statistics. Studeny et al (2011) used the family of divergence measures to evaluate the degree of departure from the perfectly even abundance distribution, which serves as a null model. In this section, we derive a turnover measure based on one case of the power divergence statistics, the Kullback-Leibler (KL) divergence measure.…”

“…ν − 1 , where ν ∈ R. One advantage of using the parametric family of divergence measures is to have a parameter ν that controls the relative weighting given to common and rare species (Studeny et al 2011). ν specifies different members of the test statistic in the family.…”