Detecting competition in the fossil record: Support for character displacement among Ordovician brachiopods

In an effort to further our understanding of ecosystem structure on multiple temporal and biogeographic scales, the influence of competitive interactions in an invasive setting was explored in the fossil record. Using brachiopod morphology as a proxy for niche space occupation, the external shapes of three pairs of potentially competing brachiopod species were analyzed via three-dimensional baseline shape co-ordinates. Morphology of incumbents was compared before and after the Richmondian Invasion (Late Ordovician, Illinois Basin), and for each incumbent–invader pair: it was possible to differentiate the incumbents pre- and post-invasion; the incumbent became more morphologically different from the invader; and landmarks driving the morphological differences of two of the incumbents shift away from the invader in multidimensional morphospace. These results are consistent with character displacement, which supports the hypothesis that competition played a discernable role in the brachiopod community. This suggests that the use of morphometrics and morphospace occupation could provide a valuable tool for the exploration of ecological interactions in the geologic record, potentially providing novel interpretations of the effects of competition on community structure and evolution.