N90, a Diversity Index Sensitive to Variations in Beta Diversity Components

Enric Massutí,Francesc Ordines,M Teresa Farriols

doi:10.3390/d13100489

Abstract

Species diversity in a community is mainly related to the number and abundance of species that form it. N90 is a recently developed diversity index based on the results of the similarity percentage (SIMPER) analysis that represents the number of species contributing up to ninety percent of within-group similarity in a group of samples. The calculation of N90 is based on the Bray–Curtis similarity index and involves the number of species and abundances in a group of samples. We have explored the properties of N90 compared to other alpha, beta and gamma diversity indices and to beta diversity measures accounting for nestedness and turnover. We have used a non-real data set to compare the values of all indices with N90 and two real data sets of demersal fish communities along large and short depth gradients with higher influence of turnover and nestedness, respectively, to correlate the same indices with N90. The sensitivity of N90 to reductions in the frequency of occurrence and the evenness of the distribution of species abundances among samples allows the detection of diversity loss due to the fishing-induced retreatment of species populations to localities presenting the most favorable ecological conditions. This property, both in the identification of species replacement and species loss through SIMPER analysis, make N90 a useful indicator to support the Ecosystem Approach to Fisheries within the current context of global change.

Highlights

Diversity is a founding, but at the same time, complex concept in ecology
This leads to a decrease in N90 due to the retreat of species populations to the localities presenting the most favorable ecological conditions
Following the variance framework approach, we have compared N90 to beta diversity measures accounting for nestedness and turnover and to within-group similarity from similarity percentage (SIMPER) analysis

Summary

Introduction

But at the same time, complex concept in ecology. More than species diversity in the community, understood as a group of interdependent organisms of different species growing or living together in a specified habitat, diversity can be related to genetic diversity within populations or diversity of functional traits. For most ecologists, diversity has to do with the number and abundance of species in the community, and a lot of attempts have been made to express this concept numerically. A high number of diversity indices have been proposed showing different aspects of the community structure, taking into account factors ranging from the number of species and the relative abundance or biomass of these species, to the taxonomic or functional relationships between them [1]. A new family of diversity indices, known as Hill numbers, have been preferred because they have shown more desired properties than the raw form [2,3]; for example, they obey an intuitive replication principle or doubling property and they are all expressed in units of effective numbers of species [4]

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