Determining the relative roles of species replacement and species richness differences in generating beta‐diversity patterns

Abstract

Aim To determine the relative contribution of species replacement and species richness differences to the emergence of beta-diversity patterns.Innovation A novel method that disentangles all compositional differences (bcc, overall beta diversity) in its two components, species replacement (b-3) and species richness differences (brich) is proposed. The performance of the method was studied with ternary plots, which allow visualization of the influence of the relative proportions of shared and unique species of two sites over each metric. The method was also tested in different hypothetical gradients and with real datasets. The novel method was compared with a previous proposal based on the partitioning of overall compositional differences (bsor) in replacement (bsim) and nestedness (bnes). The linear response of bcc contrasts with the curvilinear response of bsor to linear gradients of dissimilarity. When two sites did not share any species, bsim was always 1 and b-3 only reached 1 when the number of exclusive species of both sites was equal. b-3 remained constant along gradients of richness differences with constant replacement, while bsim decreased. brich had a linear response to a linear gradient of richness differences with constant species replacement, whereas bnes exhibited a hump-shaped response. Moreover, bsim > bnes when clearly almost all species of one site were lost, whereas b-3 < brich in the same circumstances. Main conclusionsThe behaviour of the partition of bcc into b-3 and brich is consistent with the variation of replacement and richness differences. The partitioning of bsor into bsim and bnes overestimates the replacement component and underestimates richness differences. The novel methodology allows the discrimination of different causes of beta-diversity patterns along latitudinal, biogeographic or ecological gradients, by estimating correctly the relative contributions of replacement and richness differences.

Geographical patterns and partition of turnover and richness components of beta-diversity in faunas from Tocantins river valley

“…There is not a large difference in the overall β-diversity among the four groups of vertebrates, for both Baselga's (2010) and Carvalho et al (2012) approaches (Table 1). β SOR tends to be smaller than β cc , but their relative magnitude of difference among the groups are quite similar.…”

“…Almeida-Neto (2012), among other things, criticized the use of the term "nestedness" in this context mainly because other more specific measurements have been proposed and widely tested in a different context (e.g., Almeida-Neto et al, 2008). Carvalho et al (2012) criticized the metrics used by Baselga's (2010) and pointed out that β SIM overestimates the turnover component, and proposed different metrics for making the partition. The overall reasoning is the same, but the overall beta-diversity is computed based on Jaccard's complement, rather than Sorensen, and is given by (Equation 5)…”

“…We analyzed the dataset described above using the approaches proposed by Baselga (2010) and Carvalho et al (2012). The details of computation and derivation of the formulae used can be found in these original papers, and only a brief description of the formulae used for calculations is given below.…”

“…Despite the large interest in Baselga's (2010) approach to partition beta-diversity into distinct components, the details of the metrics used by him have been criticized on different grounds (e.g., Almeida-Neto et al, 2012;Carvalho et al, 2012), and some improvements have been proposed based on the same reasoning (Carvalho et al, 2012;but see Baselga 2012). Here we analyzed a data set of faunal similarity of terrestrial vertebrates in Central, North and Northeast Brazil to answer the following questions: 1.…”

“…Here we analyzed a data set of faunal similarity of terrestrial vertebrates in Central, North and Northeast Brazil to answer the following questions: 1. What is the difference between Baselga's (2010) and the newer approach proposed by Carvalho et al (2012) for partition of β-diversity in a real, rather than simulated or artificial, dataset? 2.…”