Exceptions to the rule: Relative roles of time, diversification rates and regional energy in shaping the inverse latitudinal diversity gradient

Abstract

Aim: Inverse latitudinal diversity gradients (i-LDGs), whereby regional richness peaks outside the tropics, have rarely been investigated, and their causes remain unclear.Here, we investigate three prominent explanations, postulating that species-rich regions have had: (1) longer time to accumulate species; (2) faster diversification; and(3) more energy to support species-rich communities. These mechanisms have been shown to explain the tropical megadiversity, and we examine whether they can also explain i-LDG. Location: Global.Time period: Contemporary.Major taxa studied: Amphibians, birds and mammals. Methods:We estimated the time for species accumulation, regional diversification rates and regional energy for six tetrapod taxa (c. 800 species). We quantified the relative effects and interactions among these three classes of variables, using variance partitioning, and confirmed the results across alternative metrics for time (community phylometrics and BioGeoBeARS), diversification rates (BAMM and DR) and regional energy (past and current temperature, and productivity).Results: Although regional richness across each of the six taxa peaked in the temperate region, it varied markedly across hemispheres and continents. The effects of time, diversification rates and regional energy varied greatly from one taxon to another, but high diversification rates generally emerged as the best predictor of high regional richness. The effects of time and regional energy were limited, with the exception of salamanders and cetaceans.Main conclusions: Together, our results indicate that the causes of i-LDG are highly taxon specific. Consequently, large-scale richness gradients might not have a universal explanation, and different causal pathways might converge on similar gradients. Moreover, regional diversification rates might vary dramatically between similar environments and, depending on the taxon, regional richness might or might not depend

Evolutionary history and global angiosperm species richness–climate relationships

“…Therefore, to evaluate whether the selection of different methods for the estimation of net diversification rates may have impacted our results, we repeated our analysis using two different methods, namely the DR and BAMM methods. Both methods are sufficiently popular, and the tip diversification rates estimated by both methods have shown to be robust (Cerezer et al, 2022; Title & Rabosky, 2019). Interestingly, the results based on these two methods are highly consistent, suggesting that the choose of a specific method of net diversification rate estimation did not bias our findings.…”

CHELSA-TraCE21k – high-resolution (1 km) downscaled transient temperature and precipitation data since the Last Glacial Maximum

“…Transient long-term climatic data have a wide range of possible applications, ranging from population genetics (Leugger et al, 2022;Yannic et al, 2020), community ecology (Staples et al, 2022), and biodiversity buildup (Garcés-Pastor et al, 2022;Alsos et al, 2022) to evolutionary biology (Cerezer et al, 2022), just to name a few. Here we use one application in paleoecology as a plausibility test to additionally check if the transient CHELSA-TraCE21k data can reliably detect known LGM refugia of plant species.…”

Same process, different patterns: pervasive effect of evolutionary time on species richness in freshwater fishes

“…Worldwide, tropical regions harbour an extraordinary number of species compared with temperate regions, forming the basis for the latitudinal diversity gradient (LDG), one of the best-studied and widely recognized patterns across taxa [1,2]. Nevertheless, this nearly ubiquitous pattern is not followed by some taxa nor consistent across phylogenetic and spatial scales, with inverse LDGs in which diversity peaks are located outside the tropics [3][4][5]. These inverse LDGs have been explained as resulting from clades' characteristics such as evolutionary history, biogeographical origin, as well as physiological and ecological requirements [3,6].…”

“…fast speciation and low extinction in species-rich regions [8,9]) and the time-for-speciation hypothesis (i.e. longer colonization/ origination time allowing greater species accumulation in species-rich regions [11,20]) have been suggested to explain both expected and inverse LDG patterns in tetrapods [3,24]. Although similar processes might lead to different patterns, deviations from the LDG have been explained by differences in ecological and physiological requirements, dispersal capacities and reproductive modes of taxa [3,25,28,30].…”

“…longer colonization/ origination time allowing greater species accumulation in species-rich regions [11,20]) have been suggested to explain both expected and inverse LDG patterns in tetrapods [3,24]. Although similar processes might lead to different patterns, deviations from the LDG have been explained by differences in ecological and physiological requirements, dispersal capacities and reproductive modes of taxa [3,25,28,30]. Thus, reconciling our understanding on the causes driving different LDG patterns requires a deconstructive approach allowing us to compare among different clades and relate the potential differences with their particular properties such as biogeographic history or ecological traits to infer the underlying drivers and processes.…”