What explains patterns of species richness? The relative importance of climatic‐niche evolution, morphological evolution, and ecological limits in salamanders

Abstract

A major goal of evolutionary biology and ecology is to understand why species richness varies among clades. Previous studies have suggested that variation in richness among clades might be related to variation in rates of morphological evolution among clades (e.g., body size and shape). Other studies have suggested that richness patterns might be related to variation in rates of climatic‐niche evolution. However, few studies, if any, have tested the relative importance of these variables in explaining patterns of richness among clades. Here, we test their relative importance among major clades of Plethodontidae, the most species‐rich family of salamanders. Earlier studies have suggested that climatic‐niche evolution explains patterns of diversification among plethodontid clades, whereas rates of morphological evolution do not. A subsequent study stated that rates of morphological evolution instead explained patterns of species richness among plethodontid clades (along with “ecological limits” on richness of clades, leading to saturation of clades with species, given limited resources). However, they did not consider climatic‐niche evolution. Using phylogenetic multiple regression, we show that rates of climatic‐niche evolution explain most variation in richness among plethodontid clades, whereas rates of morphological evolution do not. We find little evidence that ecological limits explain patterns of richness among plethodontid clades. We also test whether rates of morphological and climatic‐niche evolution are correlated, and find that they are not. Overall, our results help explain richness patterns in a major amphibian group and provide possibly the first test of the relative importance of climatic niches and morphological evolution in explaining diversity patterns.

Genome size variation and species diversity in salamanders

“…A significant relationship has previously been reported between diversification rate and niche rate in 15 plethodontid clades (Kozak & Wiens, ). Using the values of niche rate for plethodontids reported in Kozak and Wiens (), we found a significant association between C‐value and niche rate at this lower taxonomic level ( F 1,13 = 13.95, p = 0.002, R 2 = 0.48; Table ), similar to what was observed at the family level ( F 1,8 = 13.32, p = 0.006, R 2 = 0.58; Table ). In contrast, we did not find that C‐value is associated with either crown age, geographic area, diversification rate or species diversity in the plethodontid clade (Table ).…”

“…The univariate and multivariate pgls analysis was carried out in R with the caper package. The maximum likelihood value of lambda was allowed to vary, whereas kappa and delta were set to 1 as in Kozak and Wiens (Kozak & Wiens, ). For the pgls analysis, we used the time‐calibrated family or genus tree obtained from the amphibia tree of Pyron and Wiens (Pyron & Wiens, ) as described above, or the phylogenetic tree from Kozak and Weins (Kozak & Wiens, ) for the Plethodontidae data set.…”

Increased diversification rates are coupled with higher rates of climate space exploration in Australian Acacia (Caesalpinioideae)

“…We employed previously published (González‐Orozco et al , ) estimates of central tendencies of responses (Saupe et al , ) for each environmental variable from georeferenced herbarium vouchers. Similar approaches have been used in a number of comparative phylogenetic analyses (Ackerly et al , ; Rabosky & Adams, ; Kozak & Wiens, , ; Cooper et al , ).…”

Macroevolution of desiccation‐related morphology in plethodontid salamanders as inferred from a novel surface area to volume ratio estimation approach

“…In this study, we presented strong evidence of a morphological response to ecological selective pressures in a family of salamanders whose morphology is not often associated with differences in habitat (Kozak and Wiens ). Previous investigations into the macroevolution of morphology have largely concluded that variation in plethodontid body proportions across taxa do not always correspond to what is predicted by selection across environmental gradients (Adams et al.…”