Large-scale phylogenetic analyses reveal the causes of high tropical amphibian diversity

Abstract

Many groups show higher species richness in tropical regions but the underlying causes remain unclear. Despite many competing hypotheses to explain latitudinal diversity gradients, only three processes can directly change species richness across regions: speciation, extinction and dispersal. These processes can be addressed most powerfully using large-scale phylogenetic approaches, but most previous studies have focused on small groups and recent time scales, or did not separate speciation and extinction rates. We investigate the origins of high tropical diversity in amphibians, applying new phylogenetic comparative methods to a tree of 2871 species. Our results show that high tropical diversity is explained by higher speciation in the tropics, higher extinction in temperate regions and limited dispersal out of the tropics compared with colonization of the tropics from temperate regions. These patterns are strongly associated with climate-related variables such as temperature, precipitation and ecosystem energy. Results from models of diversity dependence in speciation rate suggest that temperate clades may have lower carrying capacities and may be more saturated (closer to carrying capacity) than tropical clades. Furthermore, we estimate strikingly low tropical extinction rates over geological time scales, in stark contrast to the dramatic losses of diversity occurring in tropical regions presently.

Rates of ecological divergence and body size evolution are correlated with species diversification in scaly tree ferns

“…This means that increased diversification rates coupled to high rates of evolution have appeared repeatedly within the Cyatheaceae, exemplified by Cyathea in South America [33][34][35] and Sphaeropteris in Malesia [32]. However, the same rates of diversification can be achieved with different combinations of absolute extinction and speciation rates [4,22,53]. Ideally, given a sufficient number of sampled species, absolute rates of extinction and speciation can be confidently estimated from a phylogeny [4,47,53].…”

“…Geographical variation in species richness among clades has been widely documented, but explaining the causes of these differences remains one major challenge in evolutionary biology [1][2][3][4][5][6]. In general, differences in species richness can be associated with heterogeneity in the rates of species diversification, but the drivers of such rate heterogeneity remain poorly explored for many groups of species.…”

Explaining large-scale patterns of vertebrate diversity

“…Many vertebrate clades do show a strong latitudinal diversity gradient (e.g. amphibians and mammals; [2,3]). However, the most species-poor of these 12 major vertebrate clades are aquatic clades that occur almost exclusively in tropical regions (e.g.…”

“…To clarify, numerous studies have tested the causes of richness patterns within major vertebrate clades, such as the latitudinal richnesss gradient within amphibians and mammals (e.g. [2,3]). However, few studies have addressed the dramatic variation in richness across these clades.…”

Reconsidering the Loss of Evolutionary History: How Does Non-random Extinction Prune the Tree-of-Life?

“…Purvis et al 2000aPurvis et al , 2005Isaac et al 2007Isaac et al , 2012Faith 2008 ). This effort has been facilitated by the rapid rise in analytical tools, and the availability of large comprehensive phylogenetic trees for well studied taxonomic groups such as mammals (Bininda-Edmonds et al 2007 ), birds (McCormack et al 2013 ), amphibians (Pyron and Wiens 2013 ), and fl owering plants (e.g. Davies et al 2004 ).…”