METABOLISM, ENERGY, AND MASS EXTINCTIONS: HOW DOES ORGANISMAL METABOLIC ACTIVITY AFFECT SUSCEPTIBILITY TO EXTINCTION IN THE MARINE REALM?

Due to the interplay between temperature, oxygen supply, and metabolic performance, organismal metabolic rate is expected to play a major role in determining survival, particularly during conditions of rapid climate warming. We use a model of resting metabolic rate based on biomass and environmental temperature (Gillooly et al. 2001) to estimate the metabolic rates of extinct taxa, for which respiration rates and activity levels cannot be directly measured. Previous work indicates that bivalves with higher total metabolic rates are generally less likely to go extinct in the post-Paleozoic fossil record, whereas bivalves with higher mass-standardized metabolic rates are in contrast at greater risk of extinction, a pattern of extinction selectivity which is magnified during hyperthermals, episodes of rapid climate warming in the geologic record which serve as useful analogues to modern anthropogenic climate change. The metric of resting metabolic rate is distinct from maximum metabolic rate and aerobic scope, and on its own may not paint a complete picture of activity levels and energetics. The survival of an organism may be dependent on its metabolic familiarity with internal hypoxia, hypercapnia, and pH imbalances, or, conversely, on limitations to highly active behaviors such as feeding or movement. Here, we consider whether other marine invertebrate clades display similar trends to bivalves with regards to resting metabolic rate and extinction, and how such trends compare with other aspects of metabolism, such as relative activity levels.