CAN "COMMUNITY STRUCTURE" ARISE TAPHONOMICALLY? EVALUATING HUTCHINSONIAN RATIOS IN THE FOSSIL RECORD

Biotic interactions, such as competition, are among the primary agents structuring modern ecological communities. A uniformitarian view would suggest similar dynamics for paleocommunities, but demonstrating such a causal relationship through deep time has hitherto proven daunting. Novel documentation of strophomenide brachiopod paleocommunity structure in the Liberty Member of the Dillsboro Formation (Upper Ordovician, SE Indiana) implicates a strong organizing role for competition. Morphometric evidence for such a strong role includes (1) statistically significant (p<0.03) minimization of niche overlap throughout the strophomenide brachiopod guild and (2) statistically significant (p<0.03) uniformity among niche partition widths throughout the guild. Might these results represent mere taphonomic artifacts? If differential taphonomy and time-averaging act in such a way as to overwhelm biological patterns, then the observed patterns might in fact be taphonomic, not biological, in origin. To answer the question "Could niche partitions as uniform as those observed ever arise from taphonomic processes alone?" we randomly time-averaged and differentially taphonomized sets of simulated communities generated according to one of three models of community dynamics: (1) brachiopod populations always exhibit effectively random niche partitions; (2) populations exhibit uniform niche partitions only when they cooccur in the same community; (3) populations always exhibit niche partitions uniform within communities but variable across communities. In every scenario, our observed niche partition uniformity was found to be statistically unlikely (p<0.05) to be due to taphonomic processes.

Through the above simluations we demonstrate that niche partition uniformity, when observed in the fossil record, cannot have been generated taphonomically. The initial, empirical results stand as evidence of a biological pattern demanding an explanation at the level of ecological process: community organization by competition. In addition, they suggest that biotic interactions, such as competition, have been important in structuring communities throughout the last 450 million years.