Metabolic rates, climate and macroevolution: a case study using Neogene molluscs

Basal metabolic rate (BMR) is posited to be a fundamental control on the structure and dynamics of ecological networks, influencing organism resource use and rates of senescence. Differences in the maintenance energy requirements of individual species therefore potentially predict extinction likelihood. If validated, this would comprise an important link between organismic ecology and macroevolutionary dynamics. To test this hypothesis, the BMRs of organisms within fossil species were determined using body size and temperature data, and considered in the light of species' survival and extinction through time. Our analysis focused on the high-resolution record of Pliocene to recent molluscs (bivalves and gastropods) from the Western Atlantic. Species-specific BMRs were calculated by measuring the size range of specimens from museum collections, determining ocean temperature using the HadCM3 global climate model, and deriving values based on relevant equations. Intriguingly, a statistically significant difference in metabolic rate exists between those bivalve and gastropod taxa that went extinct and those that survived throughout the course of the Neogene. This indicates that there is a scaling up from organismic properties to species survival for these communities. Metabolic rate could therefore represent an important metric for predicting future extinction patterns, with changes in global climate potentially affecting the lifespan of individuals, ultimately leading to the extinction of the species they are contained within. We also find that, at the assemblage level, there are no significant differences in metabolic rates for different time intervals throughout the entire study period. This may suggest that Neogene mollusc communities have remained energetically stable, despite many extinctions.