The use of taxonomic distinctness indices in assessing patterns of biodiversity in modular organisms

Abstract

Estimating diversity of modular organisms may be problematic due to actual difficulties in discriminating between ‘individuals’ and quantifying their abundances. Quantitative data, when available, are collected through methods that could preclude the application of classical diversity indices, making comparisons among studies difficult. Taxonomic distinctness indices, such as the ‘Average Taxonomic Distinctness’ (Δ+) and the ‘Variation in Taxonomic Distinctness’ (Λ+) may represent suitable tools in investigating diversity beyond the simple species number. The potential usefulness of such indices has been explored almost exclusively on unitary organisms, neglecting modular ones. In this study, we employed Δ+ and Λ+ to analyse patterns of diversity of epiphytic hydroid assemblages living on Cystoseira seaweeds at a hierarchy of spatial scales, along 800 km of rocky coast (SE Italy). ANOVA on species richness and Λ+ showed no significant difference in sample diversity at the investigated spatial scales. In contrast, there were significant differences at the scale of 10s of km in Δ+. Analyses based on simulations detected significant variations at all spatial scales in Δ+. Such findings underline the potential of Δ+ in highlighting relevant spatial scales of variation in patterns of hydroid diversity. Our results also suggest that the interplay between natural environmental variations and the complex ecological traits of modular organisms might affect taxonomic distinctness indices. We stress the need for further investigations focusing on modular organisms before any generalizations on the use of taxonomic relatedness measures in examining marine biodiversity can be made.

Morphospecies and taxonomic sufficiency of benthic megafauna in scientific bottom trawl surveys

“…Species in environment-rich systems will likely occupy a wider range of ecological niches than species inhabiting systems with less environmental heterogeneity (Baldi, 2008;Connor and McCoy, 1979), which might explain the decreasing gradient of taxonomic sufficiency as we move from "species-poor" ecosystems towards "species-rich" ones. It is worth mentioning that although the ARI values decrease in these large ecosystems, the range of absolute values is still highly satisfactory and comparable to other studies (Bevilacqua et al, 2009;Soares-Gomes et al, 2012;Wlodarska-Kowalczuk and Kedra, 2007).…”

Missing species among Mediterranean non-Siphonophoran Hydrozoa

“…Δ + represents the average taxonomic path length between two randomly chosen species in the taxonomic tree, whereas Λ + reflects the unevenness in the taxonomic tree of a given species’ list and represents the variance of these pair-wise path lengths. The indices are independent of the number of species in a sample and thus represent useful tools for analysing historical data (Bevilacqua et al 2009 ). A reference list, from species to subclass, was made including all NSH species recorded.…”

Comparison of the temporal and taxonomic patterns of ichthyofauna captured with a fyke net in two sheltered environments in southern Brazil

“…The use of these indexes is still restricted in the marine environment. To date, they have essentially been employed in environmental impact assessments (Bevilacqua et al, 2009), with the assumption that disturbed assemblages are taxonomically poorer than undisturbed assemblages (Warwick & Clarke, 1995). The application of the combination of AvTD and VarTD may enable a robust summary of the patterns of taxonomic relatedness within the assemblage to be obtained (Clarke & Warwick, 2001) based on the uniformity of the taxon distribution within a hierarchical taxonomic tree (Xiujuan et al, 2010).…”