Indices for assessing coral reef fish biodiversity: the need for a change in habits

Abstract

We present the first representative and quantified overview of the indices used worldwide for assessing the biodiversity of coral reef fishes. On this basis, we discuss the suitability and drawbacks of the indices most widely used in the assessment of coral fish biodiversity. An extensive and systematic survey of the literature focused on coral reef fish biodiversity was conducted from 1990 up to the present. We found that the multicomponent aspect of biodiversity, which is considered as a key feature of biodiversity for numerous terrestrial and marine ecosystems, has been poorly taken into account in coral reef fish studies. Species richness is still strongly dominant while other diversity components, such as functional diversity, are underestimated even when functional information is available. We also demonstrate that the reason for choosing particular indices is often unclear, mainly based on empirical rationales and/or the reproduction of widespread habits, but generally with no clear relevance with regard to the aims of the studies. As a result, the most widely used indices (species richness, Shannon, etc.) would appear to be poorly suited to meeting the main challenges facing the monitoring of coral reef fish biodiversity in the future. Our results clearly show that coral reef scientists should rather take advantage of the multicomponent aspect of biodiversity. To facilitate this approach, we propose general guidelines to serve as a basis for the selection of indices that provide complementary and relevant information for monitoring the response of coral reef fish biodiversity in the face of structuring factors (natural or anthropic). The aim of these guidelines was to achieve a better match between the properties of the selected indices and the context of each study (e.g. expected effect of the main structuring factors, nature of data available).

A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes

“…Moreover, almost all studies rely on richness (the number of taxa; Table S1) as a proxy for biodiversity but ignore metrics such as evenness (the relative abundances among species; Table S1) (e.g., Bengtsson, Ahnström, & Weibull, ; Tuck et al., ). Yet, richness poorly reflects overall community diversity (Duncan, Thompson, & Pettorelli, ; Loiseau & Gaertner, ), and its measurement is strongly confounded by abundance (Chao & Jost, ). Variation in richness has also been shown to have minimal impacts on ecosystem functioning when richness increases are driven primarily by rare species that contribute little to ecosystem services (Kleijn et al., ; Winfree, Fox, Williams, Reilly, & Cariveau, ).…”

The Full Hierarchical Structuration of Species Abundances Reliably Inferred from the Numerical Extrapolation of Still Partial Samplings: A Case Study with Marine Snail Communities in Mannar Gulf (India)

“…Moreover, this distinction even has essential implications, because it happens that the pattern of the as-observed unevenness cannot faithfully mirror the intensity of the structuring process itself, since the level of unevenness is also influenced, purely mathematically [26,27], by the species richness of the community. An important point indeed, already argued previously [12,13,[26][27][28] but, yet, still remaining ignored too frequently in common practice. This systematic -and biologically irrelevant -influence, should thus be set aside if the true biological meaning of abundance unevenness is to be relevantly understood.…”

“…to either the log-series model or the lognormal model, respectively [10,[22][23][24][25]. Now, as regards the intensity of the structuring process, it is first necessary to remind that the degree of unevenness U is inadequate in this respect, due to its additional mathematical dependence upon the species richness S t [26,27] (see also Appendix 3), which ultimately results in masking the genuine contribution of the structuring process itself [12,13,28]. To get rid of this spurious dependence, deprived from biological significance, it has been shown appropriate to cancel its influence by comparing the actual "S.A.D."…”

Disentangling and Quantifying the Functional Determinants of Species Abundance Unevenness in Ecological Communities

“…of a local community of species is usually presented graphically, with the (as a rule, logtransformed) relative abundances 'a i ' of species plotted against the rank 'i' of these species, ordered by decreasing level of abundance. S.A.D.s are a fundamental tool helping to investigate and to get an overall understanding of the internal organization within ecological communities, on both the descriptive and the functional points of view [18][19][20][21][22][23][24][25][26].…”