ECOLOGICAL STASIS IN THE MIDDLE DEVONIAN HAMILTON FAUNA: HOW STABLE ARE SPECIES INTERACTIONS?

The Middle Devonian Hamilton Fauna of New York State has been the case study area for Coordinated Stasis over the last quarter century. This time period is characterized by taxonomic persistence and low rates of morphological change within lineages. Especially controversial has been the question of the presence or absence of ecological stasis, because mere taxonomic persistence does not necessarily imply that these communities are ecologically stable. In the past, rank-order abundance and trophic guild structure have been presented as evidence for ecological stasis. Here, we investigated ecological stability in a new way, by using a ‘community module’ approach to track community response to environmental change, which simplifies the complexity of community structures by focusing on a distinct set of strong and common species interactions to help understand the dynamics of the system as a whole. We focused on repair scars in the epifaunal bivalve community as a proxy for a strong species interaction---predation--- in the Hamilton Fauna. We collected material from seven localities comprising the Middle Devonian Skaneateles and Ludlowville Formations. Sampling sites were chosen to sample the calcareous siltstone biofacies in which these bivalves occur. We calculated rank-order abundance of bivalve taxa and repair frequency (percent of shells with at least one scar) for each sample. As with other studies our preliminary results indicate that rank-order abundance in the different localities was similar, with the coarsely ribbed ptychopteriids being the dominant species followed by the smooth Glyptodesma and Actinopteria that develops fine radial and commarginal ornamentation. Our preliminary predation results show that between 8 and 20% of the bivalve fauna preserves repair scars, with scarring frequency fluctuating non-directionally throughout the study time interval. If this pattern holds after further sampling, it would indicate that species interactions within the Hamilton Fauna were stable for a long period of time, supporting the notion of ecological stasis.