Explanations for latitudinal diversity gradients must invoke rate variation

The latitudinal variation in amphibian speciation rates revisited

Speciation can increase regional species richness, however, our knowledge of how and why speciation rates vary across space is still incomplete. Using comprehensive information on species distributions and their phylogenetic relationships, we describe the global spatial patterns of variation in amphibian speciation rates and explore their ecological determinants. We find that overall mean speciation rates in amphibians increase with latitude. This pattern is largely determined by anurans, the most diverse amphibian order. Salamanders, nevertheless, speciate faster in the tropics, whereas caecilians did not exhibit any relationship with latitude. Despite the overall inverse latitudinal trend in mean speciation rates of amphibians, tip-level maximum speciation rates are not necessarily restricted to higher latitudes and can be found in different regions across the globe. Among bioregions, higher mean speciation rates are associated with high past climatic velocity and topographic complexity, both factors potentially promoting isolation, an important primer for speciation. Our results suggest that the emerging inverse pattern of speciation rates in amphibians is likely driven by the combination of a few rapidly speciating clades distributed in higher latitudes and numerous clades in lower latitudes showing heterogeneous rates that, when averaged, pull down the estimations of mean speciation in the areas where they occur.

The macroecology of Mesozoic dinosaurs

Dinosaurs thrived for over 160 million years in Mesozoic ecosystems, displaying diverse ecological and evolutionary adaptations. Their ecology was shaped by large-scale climatic and biogeographic changes, calling for a 'deep-time' macroecological investigation. These factors include temperature fluctuations and the break up of Pangaea, influencing species richness, ecological diversity and biogeographic history. Recent improvements in the dinosaur fossil record have enabled large-scale studies of their responses to tectonic, geographic and climatic shifts. Trends in species diversity, body size and reproductive traits can now be analysed using quantitative approaches like phylogenetic comparative methods, machine learning and Bayesian inference. These patterns sometimes align with, but also deviate from, first-order macroecological rules (e.g. species-area relationship, latitudinal biodiversity gradient, Bergmann's rule). Accurate reconstructions of palaeobiodiversity and niche partitioning require ongoing taxonomic revisions and detailed anatomical descriptions. Interdisciplinary research combining sedimentology, geochemistry and palaeoclimatology helps uncover the environmental conditions driving dinosaur adaptations. Fieldwork in under-sampled regions, particularly at latitudinal extremes, is crucial for understanding the spatial heterogeneity of dinosaur ecosystems across the planet. Open science initiatives and online databases play a key role in advancing this field, enriching our understanding of deep-time ecological processes, and offering new insights into dinosaur macroecology and its broader implications.

Late Cretaceous ammonoids show that drivers of diversification are regionally heterogeneous

Palaeontologists have long sought to explain the diversification of individual clades to whole biotas at global scales. Advances in our understanding of the spatial distribution of the fossil record through geological time, however, has demonstrated that global trends in biodiversity were a mosaic of regionally heterogeneous diversification processes. Drivers of diversification must presumably have also displayed regional variation to produce the spatial disparities observed in past taxonomic richness. Here, we analyse the fossil record of ammonoids, pelagic shelled cephalopods, through the Late Cretaceous, characterised by some palaeontologists as an interval of biotic decline prior to their total extinction at the Cretaceous-Paleogene boundary. We regionally subdivide this record to eliminate the impacts of spatial sampling biases and infer regional origination and extinction rates corrected for temporal sampling biases using Bayesian methods. We then model these rates using biotic and abiotic drivers commonly inferred to influence diversification. Ammonoid diversification dynamics and responses to this common set of diversity drivers were regionally heterogeneous, do not support ecological decline, and demonstrate that their global diversification signal is influenced by spatial disparities in sampling effort. These results call into question the feasibility of seeking drivers of diversity at global scales in the fossil record.