Searching for signals of competition in deep time: Gould & Calloway’s ‘ships that pass in the night’ revisited

Speaker: Dr Tom Roper-Smith, University of Oxford
Series: Zoology Departmental Seminar Series

Competition among organisms has both ecological and evolutionary impacts. However, whether competition shapes macroevolutionary trajectories remains a subject of ongoing debate. A classic example of faunal turnover historically attributed to competition is the apparent replacement of brachiopods by bivalves over the Phanerozoic. This transition was treated as a textbook example of competitive displacement from the mid-19th century until 1980, when Gould & Calloway analysed the richness dynamics of the two groups and dubbed them ‘ships that pass in the night’. The 46 years since have seen intense debate about what drove this turnover. Yet because previous studies have been limited by insufficient sampling, the spatiotemporal dynamics of the transition remain poorly understood, which has hampered efforts to identify its primary drivers. To address this, brachiopod–bivalve richness dynamics are analysed in a spatially and environmentally explicit framework using a newly curated dataset of more than half a million fossil occurrences. The relationship between these richness dynamics and temperature, depth and other environmental variables is then evaluated. Combined with complementary extinction-selectivity analyses and co-occurrence modelling, these analyses provide the most detailed picture of the brachiopod–bivalve transition to date, with implications for the broader debate about the role of competition in macroevolution.