Respiratory Capacity Is Twice as Important as Temperature in Explaining Patterns of Metabolic Rate Across the Vertebrate Tree of Life

Metabolic rate underlies a wide range of phenomena from cellular dynamics to ecosystem structure and function. Models seeking to statistically explain variation in metabolic rate across vertebrates are largely based on body size and temperature. Unexpectedly, these models overlook variation in the size of gills and lungs that acquire the oxygen needed to fuel aerobic processes. Here, we assess the importance of respiratory surface area in explaining patterns of metabolic rate across the vertebrate tree of life using a novel phylogenetic Bayesian multilevel modeling framework coupled with a species-paired dataset of metabolic rate and respiratory surface area. We reveal that respiratory surface area explains twice as much variation in metabolic rate, compared to temperature, across the vertebrate tree of life. Understanding the combination of oxygen acquisition and transport provides opportunity to understand the evolutionary history of metabolic rate and improve models that quantify the impacts of climate change

Sexual selection enables long-term coexistence despite ecological equivalence

Empirical data indicate that sexual preferences are critical for maintaining species boundaries, yet theoretical work has suggested that, on their own, they can have only a minimal role in maintaining biodiversity. This is because long-term coexistence within overlapping ranges is thought to be unlikely in the absence of ecological differentiation. Here we challenge this widely held view by generalizing a standard model of sexual selection to include two ubiquitous features of populations with sexual selection: spatial variation in local carrying capacity, and mate-search costs in females. We show that, when these two features are combined, sexual preferences can single-handedly maintain coexistence, even when spatial variation in local carrying capacity is so slight that it might go unnoticed empirically. This theoretical study demonstrates that sexual selection alone can promote the long-term coexistence of ecologically equivalent species with overlapping ranges, and it thus provides a novel explanation for the maintenance of species diversity