Article: Estimating biomass and energy flow of molluscs in palaeo-communities

The reconstruction and interpretation of palaeo-community structure has been based largely on the taxonomic composition and relative abundance of the perserved species. An expanded and more precise understanding of some aspects of the palaeo-community can be deduced from information on the biomass and energy flow of its preserved components. The procedural steps to calculate energy flow in a palaeo-community require as input the size-frequency distribution of each species' population, the size-age relationship for each species, and certain parameters of energy flow that have been measured for living organisms. These parameters are used to: (1) estimate biomass from size, (2) convert biomass into its caloric equivalent, (3) estimate respiration from biomass and age, (4) estimate the energy cost of reproduction from respiration and size at maturity, and (5) calculate total assimilated energy from (2), (3), and (4) above. The quantity of food consumed by an individual or population can also be estimated because ingestion can be estimated from assimilation. These estimates must be summed over the individual's life span rather than evaluated on a yearly time scale, as is normally done in ecologic studies. Therefore, calculations of energy flow may differ substantially from those elucidated in studies of recent communities. The method is used to determine the energy flow in populations of four gastropods and one bivalve from the Stone City Formation (Eocene) of east-central Texas. The relative importance of species differs considerably if assessed by their numerical abundance, their biomass, or the amount of food ingested by them over their lifetimes. For example, Hesperiturris nodocarinatus, the least abundant species numerically, ingested the most prey biomass.