Body size distributions of anurans are explained by diversification rates and the environment

Abstract

Aim Body size frequency distributions are often skewed to the right, with a greater frequency of small‐sized species. Right skewness can appear when speciation is biased towards small species and extinction towards large ones. In contrast, limits imposed by environmental constraints will select taxa to co‐occur in assemblages and can modify size distributions to the left or to the right. We analysed whether the shape of size distributions of anurans is related to diversification rates and how the environment might also be creating the observed patterns. Location The Western Hemisphere. Time period Current. Major taxa studied Anurans. Methods We computed diversification rates from a dated phylogeny and obtained data for body size, spatial distribution and the climate (annual temperature, potential evapotranspiration and normalized difference vegetation index) inhabited by 2,598 anuran species to analyse the relationship between diversification rates and body size. We then used an assemblage‐based approach to test whether the climate is acting together with species evolutionary history to generate skewed distributions of body sizes at local sites. Results Skewness was positively correlated with size‐biased speciation and extinction, whereas it was negatively correlated with net diversification. After the inclusion of environmental predictors, the explanatory power of our models increased significantly. When ranking the predictors, evolutionary rates remained first, followed by a secondary role of environmental variables. Main conclusions Despite the high frequency of right‐skewed body size distributions, anuran assemblages of the New World showed a variation of skewness that can be explained by faster net diversification (speciation minus extinction) at modal sizes. We conclude that size‐biased evolutionary rates and the environment both have a role in defining the proportion of small and large sizes at local scales.

What drives the evolution of body size in ectotherms? A global analysis across the amphibian tree of life

“…These data were collected from the primary literature, including articles and books, and from direct observation of specimens both in museums and in the field. Given that snout–vent length (SVL) is the most common proxy for body size in anurans and salamanders (Amado et al, 2021; Pincheira‐Donoso, Harvey, Grattarola, et al, 2021; Wells, 2007), whereas total body length is used for caecilians (Pincheira‐Donoso et al, 2019), we used species body mass as our measure for body size to make analyses comparable. Actual measures of body mass are considerably scarcer than body length measures both in the literature and in museum specimens.…”

Genome size does not influence extinction risk in the world's amphibians

“…These data were collected from the primary literature (peer‐reviewed articles and monographs), and from direct observation of specimens both in museums and in the field. For anurans and salamanders, we employed maximum snout–vent length as our proxy for body size, given that this is the most widely used measure for body size in these two orders (Amado et al, 2021; Pincheira‐Donoso, Harvey, Grattarola, et al, 2021; Wells, 2007). For caecilians, we used maximum total body length, which is the most widely used proxy for their body size (Pincheira‐Donoso et al, 2019).…”

Risk of extinction increases towards higher elevations across the world's amphibians

“…To address the role of life-history traits as drivers of extinction risk towards higher elevations, we employed our global dataset spanning body size, fecundity and parity mode, collected from the same sources described above. For both frogs and salamanders, snoutvent length (SVL) is the most used measure of body size (Amado et al, 2021;Johnson et al, 2023;Pincheira-Donoso, Harvey, Grattarola, et al, 2021;Wells, 2007), whereas total body length is used for caecilians (Pincheira-Donoso et al, 2019). To make analyses involving body size comparable, we converted maximum SVL and maximum total body length, respectively, into body mass using the approach presented by Pough (1980) based on order-specific allometric formulas (Pincheira-Donoso & Hodgson, 2018;Ripple et al, 2017).…”