Evolutionary time drives global tetrapod diversity

Abstract

Global variation in species richness is widely recognized, but the explanation for what drives it continues to be debated. Previous efforts have focused on a subset of potential drivers, including evolutionary rate, evolutionary time (maximum clade age of species restricted to a region), dispersal (migration from one region to another), ecological factors and climatic stability. However, no study has evaluated these competing hypotheses simultaneously at a broad spatial scale. Here, we examine their relative contribution in determining the richness of the most comprehensive dataset of tetrapods to our knowledge (84% of the described species), distinguishing between the direct influences of evolutionary rate, evolutionary time and dispersal, and the indirect influences of ecological factors and climatic stability through their effect on direct factors. We found that evolutionary time exerted a primary influence on species richness, with evolutionary rate being of secondary importance. By contrast, dispersal did not significantly affect richness patterns. Ecological and climatic stability factors influenced species richness indirectly by modifying evolutionary time (i.e. persistence time) and rate. Overall, our findings suggest that global heterogeneity in tetrapod richness is explained primarily by the length of time species have had to diversify.

Environmental factors explain the spatial mismatches between species richness and phylogenetic diversity of terrestrial mammals

“…One possible alternative is that most clades originated in the tropics and that only a few groups were able to adapt to colder environments (Wiens & Donoghue, 2004), thus explaining why lower temperatures are associated with less phylogenetically diverse assemblages. These results are supported by the evidence of tropical niche conservatism in mammals (Cooper et al, 2011;Olalla-Tárraga et al, 2011) and the positive association between temperature and clade age (Marin et al, 2018).…”

The global latitudinal diversity gradient pattern in spiders

“…As to the question of why we see latitudinal gradients-be they egg-shaped or otherwise-there is still no single clear answer to this question. Causes generally fall under biotic factors, for example, competition/predation (Terborgh, 2012), mutualism, specialization; abiotic factors, for example, primary productivity (O'Brien, Whittaker, & Field, 1998), kinetics (Brown, 2014); difficulty in adapting to harsh climates (Colwell, 2011), seasonality); geographic factors, for example, size of contiguous land masses, mid-domain effects (Terborgh, 1973); and historical factors linked to habitat stability (Fine, 2015), productivity (Jetz & Fine, 2012), or evolutionary time (Marin et al, 2018)-with over 30 hypotheses summarized in Willig et al (2003). In the case of spiders, the answer to the question undoubtedly requires the digital synthesis of a wider spectrum of knowledge, including ecophysiological traits, geographic ranges, palaeo-ecological history, and phylogenetic relationships.…”

The carrying capacity for species richness

“…This finding cannot necessarily be interpreted only in terms of carrying capacity; humid and hot environments could instead have had higher diversification rates or have been more stable, so that species of various taxa had time to accumulate and adapt to this environment. Indeed, there is evidence for a prevalence of ancient lineages in the tropics (e.g., Duchêne & Cardillo, 2015;Marin et al, 2018;McPeek & Brown, 2007;Pyron & Wiens, 2013;Qian, Jin, & Ricklefs, 2017). However, this pattern cannot be taken as evidence against species richness limits (Hurlbert & Stegen, 2014a), because these limits may themselves drive patterns of rapid diversification or a slow species accumulation (Pontarp & Wiens, 2017).…”