SCALING THEORY AND THE VARIABILITY OF TAXON ABUNDANCE, SIZE DISTRIBUTION AND TROPHIC POSITION OF SHALLOW WATER MARINE GASTROPODS

This study uses fossil marine communities from the Late Miocene of the Dominican Republic to investigate diversity and stability prior to a significant regional extinction in the Caribbean. Previous work on these communities has shown variability between samples in identity and abundance of gastropod taxa. Scaling theory predicts different relationships between abundance and body size based on the trophic position of the taxa being measured. If body size scales with food availability, as is the case for many secondary consumers that eat prey smaller than themselves, scaling between abundance and size is predicted to be steeper than for taxa that rely on energy from unstructured resources, such as plants and detritus. Here, we examine the relationship between the length of gastropod individuals and taxon abundance in four stratigraphically successive molluscan assemblages in order to answer two questions: (1) Is there a relationship between taxon size distribution and abundance? (2) Is there a relationship between size and trophic position of these taxa?

In order to explore the role of trophic position and body size, taxa are assigned to ecological guilds based on shared ecological characteristics: position on substrate, mode of feeding, and predators. Trophic position is determined by the number of steps between a taxon and the producers, or detritus, at the base of the food web. Families examined are Cerithiidae (epifaunal herbivores), Marginellide (epifaunal browsing carnivores), Turridae (epifaunal predatory carnivores), Retusidae (infaunal herbivores), Naticidae (infaunal predatory carnivores) and Olividae (infaunal carnivores/scavengers). This type of analysis, combining taxon abundances, body sizes and trophic properties into a single study, may shed further light on variability in both the structure of these communities and the role of trophic interactions in perpetuating or dampening disturbances in biological communities.