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)

Abstract

The detailed analysis of Species Abundance Distributions ("S.A.D.s") can shed light on how member-species organize themselves within communities, provided that the complete distribution of species abundances is made available first. In this perspective, the numerical extrapolation applied to incomplete "S.A.D." can effectively compensate for S.A.D.s incompleteness, when having to deal with substantially incomplete samplings. Indeed, almost as much information can be released from extrapolated "S.A.D.s" as would be obtained from truly complete "S.A.D.s", although the taxonomic identities of unrecorded species remain of course ignored by numerical extrapolation. To take full advantage of this new approach, a recently developed procedure allowing the leastbiased numerical extrapolation of "S.A.D.s" has been applied to three partially sampled gastropods communities associated to coral-reef in Mannar Gulf (S-E India). The following main results were derived from the three numerically completed "S.A.D.s": (i) once AJEE, 7(3): 1-27, 2018; Article no.AJEE.43918 2 completed, all three numerically "S.A.D.s" fairly well comply with the log-normal model, suggesting that, in all three communities, the process of hierarchical structuration of species abundances likely involves the combined contributions of many independent factors; (ii) moreover, the same holds true for each of the two coexisting feeding guilds (primary and secondary consumers) considered separately; (iii) when compared to secondary consumers, the guild of primary consumers has a much lower species richness but, on the other hand, exhibits a more strongly structured distribution of species abundances, which materializes not only in term of the apparent unevenness of species abundances but also after having disentangled the genuine intensity of the underlying process driving the hierarchical structuration. All the preceding features are shared in common by the three communities studied, in line with the similarity of their environmental contexts. Only minor features can actually slightly distinguish between communities, reflecting the difference in distances between them. Original Research Article

Influence of Coral-reef Complexity on Species Richness and the Hierarchical Structuration of Species Abundances in Reef fish Communities: A Case Study in South-east Brazil

“…Previous studies have highlighted a generally positive influence of coral habitat complexity on the species richness of the associated reef fish communities [7,10,11,8,12,13,14,15,16,9,[60][61][62][63]]. Yet, most of these results suffered from the bias resulting from the (hardly avoidable) incompleteness of the samplings on which they are based [11,8,43,[64][65][66][67]. Thus, as in preceding reports dealing with coral reef-associated communities [11,8,43,[64][65][66][67], numerical extrapolations were implemented to compensate for the lack of exhaustivity of available samplings, thus providing least-biased estimates of the number of unrecorded species and their respective abundances.…”

“…Yet, most of these results suffered from the bias resulting from the (hardly avoidable) incompleteness of the samplings on which they are based [11,8,43,[64][65][66][67]. Thus, as in preceding reports dealing with coral reef-associated communities [11,8,43,[64][65][66][67], numerical extrapolations were implemented to compensate for the lack of exhaustivity of available samplings, thus providing least-biased estimates of the number of unrecorded species and their respective abundances. Thereby, the fullrange of the Species Abundance Distribution is derived, including the set of species that had remained undetected.…”