Niche conservatism and elevated diversification shape species diversity in drylands: evidence from Zygophyllaceae

Abstract

The integrated contributions of climate and macroevolutionary processes to global patterns of species diversity are still controversial in spite of a long history of studies. The niche conservatism hypothesis and the net diversification rate hypothesis have gained wide attention in recent literature. Many studies have tested these two hypotheses for woody species in humid forests; however, the determinants of species diversity patterns for arid-adapted plants remain largely ignored. Here, using a molecular phylogeny and the global distributions of Zygophyllaceae, a typical arid-adapted plant family, we assessed the effects of contemporary climate and net diversification rates on species diversity patterns in drylands. We found the variables representing water availability to be the best predictors for Zygophyllaceae diversity. Specifically, Zygophyllaceae species diversity significantly decreased with the increase in water availability, probably owing to phylogenetic conservatism of water-related niches. The net diversification rates of Zygophyllaceae accelerated sharply in the recent 10 Myr, coinciding roughly with the period of global aridification. The species diversity of Zygophyllaceae significantly increased with the increase in mean net diversification rates per geographical unit, especially in the Old World, supporting the net diversification rate hypothesis. Our study provides a case exploring climatic and evolutionary mechanisms of dryland species diversity patterns, and suggests that the conservatism in water-related niches and elevated net diversification rates in drylands may have jointly determined the global patterns of dryland species diversity.

Historical assembly of Zygophyllaceae in the Atacama Desert

“…Our results are largely congruent with previous phylogenetic analyses of the Zygophyllaceae. Only the position of the monotypic Seetzenioideae differs between ML and Bayesian analyses, as previously shown (Sheahan and Chase 2000, Wang et al 2018, Wu et al 2018. The time of origin of Zygophyllaceae Figure 1, with maximum area set to 2 (calibrations scheme 2).…”

“…This study takes previous phylogenetic studies on Zygophyllaceae as the starting point (Godoy-Bürki et al 2018, Wu et al 2018. We expand the sampling of South American taxa based on field studies and herbarium material to understand the historical assembly of Zygophyllaceae in the Atacama Desert.…”

Recent accelerated diversification in rosids occurred outside the tropics

“…3). These differences among subclades may reflect phylogenetic constraints imposed by ancestral temperature niche and other factors 62 . Nevertheless, temperature is negatively associated with diversification not only in largely temperate clades such as Rosales and Fabales, but also in large clades such as Malpighiales, in which more species diversity is tropical (52.76% are tropical under more conservative Köppen-Geiger definitions 43 ; 67.21% under geographic definition; see Supplementary Table 1); even in clades that are primarily tropical, tip rates tend to be highest in non-tropical species (Fig.…”

“…Ecological opportunity due to Earth's dynamic climatic past has been frequently invoked to explain high diversification rates in species currently inhabiting temperate 14,[69][70][71]74 and arid 62,75 environments. Significantly, these studies do not typically invoke adaptive radiations.…”

The Importance of Including Soil Properties When Disentangling the Drivers of Species Richness: The Case of the Alpine Genus Saxifraga L. in China

“…Results of variance partitioning confirm that environmental energy, soil, and habitat heterogeneity are the primary determinants of the Saxifraga species richness patterns. We further established a negative relationship of energy-alpine species richness and an insignificant relationship of waterspecies richness, which suggested considerable discrepancy of climate impacts on species richness between alpine herbs and woody plants/lowland regions at large scale (Wang et al, 2009(Wang et al, , 2018Liu et al, 2017). In comparison with other landforms, orogenic dynamics promoted habitat heterogeneity and fostered the distinctive soil properties and novel habitats in mountain regions by surface uplift, runoff, and erosions, thereby resulting in the increase in diversification rate and exceptionally high species richness (Rahbek et al, 2019a).…”