Measures of taxonomic distinctness do not reliably assess anthropogenic impacts on intertidal mollusc communities

Abstract

Indices of taxonomic distinctness measure the taxonomic breadth of a community and may be more sensitive to human impacts than conventional diversity indices. They have the advantage of being, in theory, insensitive to sampling effort and can be calculated using presence/absence data. The average taxonomic distinctness index and variation in taxonomic distinctness index were used to assess the effects of putative human impacts on molluscan community composition at 63 rocky intertidal platforms on the coast of Victoria, Australia. The use of 2 sampling techniques, viz. timed searches and quadrats, was compared. Sites exposed to sewage discharge maintained high taxonomic distinctness, and those exposed to high levels of human visitation did not have consistently lower values than controls. Results varied, sometimes markedly, depending on which survey technique was used. Neither average taxonomic distinctness nor its variance were strongly correlated with large-scale environmental gradients, small-scale habitat differences or other diversity indices. It is most likely that taxonomic distinctness measures did not discriminate sites exposed to putative disturbance because of the high taxonomic diversity of intertidal mollusc assemblages, and because low values of taxonomic distinctness were not exclusive of impacted conditions.

A review of Italian research on free-living marine nematodes and the future perspectives on their use as Ecological Indicators (EcoInds)

“…They found that the index is strongly affected by natural variability, habitat features, and biogeographic context. Moreover, since specific areas or habitats may have taxonomic distinctness values that are intrinsically lower than others, significantly reduced taxonomic breadth does not necessarily point to perturbed conditions (Costa et al, 2010;Bevilacqua et al, 2011). Disentangling intrinsic effects on taxonomic distinctness from those related to human perturbations appears difficult.…”

Species diversity, trophic structure, and taxonomic distinctness of molluscan assemblages associated with Sargassum beds in a historically impacted bay

“…For molluscan assemblages, Terlizzi et al (2005) found higher values of taxonomic distinctness in control than in impacted locations. Costa et al (2010) did not consider the measurements of taxonomic distinctness calculated on presence-absence data as sensitive to human disturbance but suggests that those indexes based on abundance data might be more sensitive.…”

Measuring ecosystem degradation through half a century of fish species introductions and extirpations in a large isolated lake

“…Testing the sensitivity of taxonomic distinctness indices in discriminating anthropogenic impacts was the subject of a number of studies, but they yielded inconsistent results. Their sensitivity to human disturbances was shown in some studies (Campbell et al, 2011;Milosevic et al, 2012;Miranda et al, 2005), but not in others (Abellan et al, 2006;Costa et al, 2010;Leira et al, 2009).…”