RELATING ECOLOGY TO MACROEVOLUTION USING METABOLIC RATES OF NEOGENE MOLLUSC COMMUNITIES

Basal metabolic rate 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 basal metabolic rates of organisms within fossil species were determined using body size and temperature data, and considered in light of species’ survival and extinction through time. Our analysis focused on the high-resolution record of Pliocene to recent mollusks (bivalves and gastropods) from the Western Atlantic. Species-specific basal metabolic rates 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, no statistically significant difference in metabolic rate was found between those bivalve and gastropod taxa that went extinct and those that survived throughout the course of the Neogene. This indicates that there is not a simple scaling up from organismic properties to species survival for these communities; instead, a constellation of population or species-level factors, including size of geographic area occupied, might be implicated. We also find that, at the community level, metabolic rates are maintained throughout the study period. This suggests that Neogene mollusc communities have remained energetically stable, despite many extinctions. Together, these findings support a distinction between phenomena in the ecologic and genealogic hierarchies. Thus, understanding metabolic rate for fossil communities can provide crucial insight into extinction as an ecological and genealogical phenomenon.