From alpha to beta functional and phylogenetic redundancy

Abstract

Plot‐level redundancy or alpha redundancy is usually defined as the fraction of species diversity not expressed by functional or phylogenetic diversity. Redundancy is zero when all species in one plot are maximally dissimilar from each other. In contrast, redundancy tends to its maximum if the functional or phylogenetic differences between species tend to be minimal. To explore the ecological drivers of community assembly, ecologists also use dissimilarity measures between pairs of plots (a component of beta diversity). Traditional dissimilarity measures summarize compositional differences between pairs of plots based either on species presence and absence data or on species abundances, thus attributing equal distinctiveness between any two species. In the last decades a number of dissimilarity measures which incorporate information on functional or phylogenetic differences among species have been proposed. On the basis of such improved measures, we can define an index of beta redundancy for a pair of plots as the fraction of species dissimilarity not expressed by functional or phylogenetic dissimilarity. A necessary condition to get a meaningful index of beta redundancy is that for a given pair of plots, the functional or phylogenetic dissimilarity is always lower or equal to the corresponding species dissimilarity. However, many of the existing indices of functional or phylogenetic dissimilarity can lead to values greater than for species dissimilarity. The aim of this paper was thus to introduce a new family of tree‐based measures of phylogenetic and functional dissimilarity that conform to this requirement. To show the behaviour of the proposed measures, a worked example with data on Alpine vegetation is used.

Concepts and applications in functional diversity

“…In a similar vein, some authors interpreted dispersion as a measure of the functional redundancy (see Rosenfeld, 2002b;Wellnitz & Poff, 2001). Theoretically, less redundant communities should be those characterized by more relaxed ecological filters, and vice versa (Ricotta, Laroche, Szeidl, & Pavoine, 2020). From the perspective of biological conservation, more functionally redundant systems should show greater resilience to perturbation, e.g., when facing the extinction or disappearance of a single species, the roles performed by it can easily be done by functionally close species.…”

Beta redundancy for functional ecology

“…The basic condition to obtain a meaningful and easily interpretable index of beta redundancy in the range [ 0, 1 ] is that the functional dissimilarity D F is lower (or at least not higher) than the corresponding species dissimilarity D S . In this case, beta redundancy can be calculated as (Ricotta et al, 2020): while beta uniqueness, which is the complement of beta redundancy, can be calculated as: For R β = 0, the species turnover between P and Q goes together with a corresponding functional turnover such that D F = D S . Hence, the compositional differences between P and Q mirror their functional differences.…”

“…For a pair of plots P and Q, the chief condition to get a meaningful index of beta redundancy is that the functional or phylogenetic dissimilarity D F is always lower than the corresponding species dissimilarity D S . However, many of the most popular indices of functional and phylogenetic dissimilarity violate this condition, thus leading to the paradoxical situation of a negative beta redundancy (see Ricotta et al, 2020;Appendix S1). To overcome this problem, Ricotta et al (2020) proposed a class of treebased indices of functional and phylogenetic dissimilarity between plots that conform to the condition D F ≤ D S .…”

“…However, many of the most popular indices of functional and phylogenetic dissimilarity violate this condition, thus leading to the paradoxical situation of a negative beta redundancy (see Ricotta et al, 2020;Appendix S1). To overcome this problem, Ricotta et al (2020) proposed a class of treebased indices of functional and phylogenetic dissimilarity between plots that conform to the condition D F ≤ D S . The indices are said 'tree-based' because they depend on a functional or phylogenetic tree with species as tips and branches that express functional or phylogenetic relationships between species.…”

Distance decay 2.0 – a global synthesis of taxonomic and functional turnover in ecological communities

“…1a), and the gain or loss of species does not inform about variations in functional β-diversity whenever trait redundancy is high 36 . For example, taxonomic homogenization does not lead to functional homogenization if the newly introduced species in the assemblages are functionally similar to each other 30,37,38 . The most pressing question is whether functional features explain more of the distance decay along environmental gradients than species identities, as suggested by some earlier studies [39][40][41][42][43] .…”