Multi‐site generalised dissimilarity modelling: using zeta diversity to differentiate drivers of turnover in rare and widespread species

Abstract

Summary Generalised dissimilarity modelling (GDM) applies pairwise beta diversity as a measure of species turnover with the purpose of explaining changes in species composition under changing environments or along environmental gradients. Beta diversity only captures turnover across pairs of sites and, therefore, disproportionately represents turnover in rare species across communities. By contrast, zeta diversity, the average number of shared species across multiple sites, captures the full spectrum of rare, intermediate and widespread species as they contribute differently to compositional turnover. We show how integrating zeta diversity into GDMs (which we term multi‐site generalised dissimilarity modelling, MS‐GDM), provides a more information rich approach to modelling how communities respond to environmental variation and change. We demonstrate the value of including zeta diversity in biodiversity assessment and modelling using BirdLife Australia Atlas data. Zeta diversity values for different numbers of sites (the order of zeta) are regressed against environmental differences and distance using two kinds of regressions: shape constrained additive models and a combination of I‐splines and generalised linear models. Applying MS‐GDM to different orders of zeta revealed shifts in the importance of environmental variables in explaining species turnover, varying with the order of zeta and thus with the level of co‐occurrence of the species and, by extension, their commonness and rarity. In particular, precipitation gradients emerged as drivers in the turnover of rare species, whereas temperature gradients were more important drivers of turnover in widespread species. Appreciation of the factors that drive compositional turnover across multiple sites is necessary for accommodating the full spectrum of compositional turnover across rare to common species. This extends beyond understanding drivers for pairwise beta diversity only. MS‐GDM provides a valuable addition to the toolkit of GDM, with further potential for survey gap analysis and prediction of species composition in unsampled sites.

Similar compositional turnover but distinct insular environmental and geographical drivers of native and exotic ants in two oceans

“…Multi‐Site Generalised Dissimilarity Modelling (Latombe et al, ) was used to evaluate how the number of species shared by specific n ≥ 2 islands (hereafter noted , where ) changes with differences in environmental and geographical variables. MS‐GDM relates to the average differences in environmental and geographical variables between these n ‐specific islands, and assesses this relationship by using multiple combinations of islands.…”

Measuring continuous compositional change using decline and decay in zeta diversity

“…Generalized linear and additive models, as well as spline regression, can be applied to test the response of species turnover (measured by zeta diversity) to environmental gradients (called multisite generalized dissimilarity modeling; Latombe et al. , ).…”

“…This is a consequence of plotting decay against the mean distance across the i nonoverlapping samples, with zeta of order n a single value for the average distance between all sites, and must be considered when interpreting the effect of distance on zeta diversity as the order increases (Latombe et al. ).…”

“…Combined with existing spatial regression techniques and environmental data measured at the n ‐sites, zeta diversity provides a means to differentiate drivers of compositional turnover for the full spectrum of species, from rare to common (Latombe et al. ). Such understanding is increasingly relevant to conservation strategy, with the need to manage the responses of both rare and common species to environmental change.…”

Drivers of species turnover vary with species commonness for native and alien plants with different residence times

“…) for multiple sites (Multi‐Site Generalized Dissimilarity Modelling – MS‐GDM; Latombe et al. ). Zeta diversity offers a more complete description than traditional pairwise beta metrics of turnover in that it differentiates contributions from rare (shared by only few assemblages) and widespread (shared by many assemblages) species.…”