Do Marine Mammals Diversify More Slowly Than Non-Marine Mammals?

Abstract

Aim: Species richness is generally lower in marine than in terrestrial ecosystems, but the reasons behind this disparity remain unclear. This study examines whether marine mammals diversify at a slower pace than their non-marine counterparts, aiming to shed light on the factors explaining potential diversification differences among them. Location: Global. Time Period: Contemporary. Major Taxa Studied: Mammals. Methods: We combined time-calibrated phylogenies, species distribution data, and life-history traits to compare DR variation among marine and non-marine mammals, and to assess DR correlation with ecological realm and species traits. Results: Contrary to previous findings at higher taxonomic scales, our results show that marine mammals do not exhibit lower DR than non-marine mammals, but even higher depending on the phylogenetic framework. Our regression analyses indicate that taxonomy (particularly family) is the dominant predictor of DR variation among mammals rather than the ecological realm. Still, DR appears negatively correlated with body mass in marine mammals and with range size in non-marine mammals. Besides, the geographic distribution of DR points to a more uniform pattern in marine than in non-marine artiodactyls, for which high DR values concentrate in the Northern Hemisphere. Conversely, high DR values for marine carnivores are clustered around the poles, while a more homogeneous distribution is observed across continents for their terrestrial relatives. Main Conclusions: These findings challenge the conventional view that marine ecosystems inherently constrain species diversification. Instead, they suggest that taxonomy and species-specific traits, rather than the ecological realm alone, are the primary drivers of mammalian diversification. Our study emphasizes the complexity of mammalian evolutionary patterns and the importance of integrating taxonomic, ecological, and biogeographic factors in macroevolutionary analyses.