Abstract
BackgroundExploring species richness and turnover patterns and their drivers can provide new insights into underlying mechanisms shaping community assembly, with significant implications for biodiversity conservation. Here, we explored diversity patterns of non-endemic, neo-endemic and palaeo-endemic vascular plants in Crete, Greece, a Mediterranean hotspot of plant richness and endemism. We evaluated the relationship between α-diversity and environmental (bioclimatic variables, topography), and anthropogenic variables by Generalized Additive Models, after accounting for spatial autocorrelation. Then, we quantified turnover using the novel concept of zeta diversity (the number of shared species by multiple sites), a framework which allows to explore the full spectrum of compositional turnover, the contribution of rare and widespread species to observed patterns and the underlying processes shaping them. Finally, we explored the abiotic and biotic effects, i.e. how well one category of species (non-endemics, palaeo-endemics, neo-endemics) predicts the patterns of the other categories, on zeta diversity by multi-site Generalized Dissimilarity Modelling.ResultsWe found a strong correlation between neo-endemic and palaeo-endemic α-diversity, with climate, topography, and human impact driving species richness. Zeta diversity analysis revealed a sharper decrease of shared palaeo-endemic species, followed by neo-endemics, and then by non-endemics with the number of sites considered to estimate compositional turnover. Perhaps, the narrow distributions of palaeo-endemics as relict species and often habitat specialists, thus persisting locally, and of neo-endemics that may have not reached yet their potential geographical range, resulted in the observed zeta diversity decline pattern. Deterministic processes controlled species turnover of rare non-endemic and neo-endemic species, while deterministic and stochastic processes contributed similarly to palaeo-endemic turnover. However, stochasticity dominates in the case of widespread species in all occasions. The environmental and anthropogenic variables were poor predictors of compositional turnover, especially of widespread species. However, the non-endemic species composition was correlated to rare palaeo-endemics and neo-endemics, highlighting the importance of biotic effects in driving turnover patterns.ConclusionsIt seems that centers of neo-endemism of vascular plants coincide with centers of palaeo-endemism in Crete, but species richness and species turnover are shaped by different drivers.
Highlights
Exploring species richness and turnover patterns and their drivers can provide new insights into underlying mechanisms shaping community assembly, with significant implications for biodiversity conservation
We acknowledge that literature and systematic based formulation of endemic species categories—due to lack of phylogenetic information e.g. the public database TimeTree [47] included only 34 out of the 165 species [a short description of the performed analysis to generate timed phylogeny is presented in Supplementary along with the tree generated by TimeTree (Additional file 1: Figure S1)]—is certainly a limitation of our study
Our results demonstrated that NE exhibited higher mean elevation and minimum elevation of occurrence than PE, in concordance with Trigas et al [35] suggesting that Cretan relict flora consists mostly of lowland species, while diversification at higher elevations gave rise to neoendemic species
Summary
Exploring species richness and turnover patterns and their drivers can provide new insights into underlying mechanisms shaping community assembly, with significant implications for biodiversity conservation. We quantified turnover using the novel concept of zeta diversity (the number of shared species by multiple sites), a framework which allows to explore the full spectrum of compositional turnover, the contribution of rare and widespread species to observed patterns and the underlying processes shaping them. The understanding of the diversity patterns along spatial scales provides invaluable insights into species distribution and underlying assembly processes [1,2,3] with significant implications for biodiversity conservation [4]. Zeta diversity by quantifying the overlap of species distributions across multiple sites, overcomes the limitation of the pairwise comparisons of many widely used β-diversity metrics, reflecting the full spectrum of multi-site compositional turnover patterns [19]. Zeta diversity as it is linked to all facets of diversity [25], is comparatively still in its infancy, has the potential to provide in-depth insights into the turnover patterns and the underlying community assembly processes driving them [18, 26,27,28,29], the species-area relationship [30] and the scaling of endemism [19]
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