Rarity facets of biodiversity: Integrating Zeta diversity and Dark diversity to understand the nature of commonness and rarity.

Federico Riva,Stefano Mammola

doi:10.1002/ece3.8096

Abstract

Measuring commonness and rarity is pivotal to ecology and conservation. Zeta diversity, the average number of species shared by multiple sets of assemblages, and Dark diversity, the number of species that could occur in an assemblage but are missing, have been recently proposed to capture two aspects of the commonness‐rarity spectrum. Despite a shared focus on commonness and rarity, thus far, Zeta and Dark diversities have been assessed separately. Here, we review these two frameworks and suggest their integration into a unified paradigm of the “rarity facets of biodiversity.” This can be achieved by partitioning Alpha and Beta diversities into five components (the Zeta, Eta, Theta, Iota, and Kappa rarity facets) defined based on the commonness and rarity of species. Each facet is assessed in traditional and multiassemblage fashions to bridge conceptual differences between Dark diversity and Zeta diversity. We discuss applications of the rarity facets including comparing the taxonomic, functional, and phylogenetic diversity of rare and common species, or measuring species' prevalence in different facets as a metric of species rarity. The rarity facets integrate two emergent paradigms in biodiversity science to better understand the ecology of commonness and rarity, an important endeavor in a time of widespread changes in biodiversity across the Earth.

Highlights

Measuring biodiversity change is at the heart of ecology (MacArthur, 1965; Magurran, 2004; Whittaker, 1960), a property of considerable interest being how rare or common different biodiversity units are (Gaston, 2011; Preston, 1962)
When estimated as traditional metrics, as in the Dark diversity framework (Pärtel et al, 2011), each rarity facet is calculated for each assemblage in relation to the entire set of assemblages and to its species pool (e.g., Zeta0 is equal in all assemblages, whereas Theta0 is unique to each assemblage)
When calculated as multiassemblage metrics, as in the original Zeta diversity framework (Hui & McGeoch, 2014), the rarity facets correspond to the average number of species that occur in the five rarity facets across the possible combinations of n assemblages from the full set of assemblages (Figure 3, gray rectangles; e.g., Kappa3 is the average number of species present in the study region but that are missing from sets of three assemblages because they do not belong to the species pool of those assemblages)

Summary

Introduction

Measuring biodiversity change is at the heart of ecology (MacArthur, 1965; Magurran, 2004; Whittaker, 1960), a property of considerable interest being how rare or common different biodiversity units are (Gaston, 2011; Preston, 1962). Dark and Zeta diversities are measured in different ways (Figure 1), and we develop the framework of the rarity facets of biodiversity to capitalize on both approaches.

Results

Conclusion