FOOD WEBS THROUGH TIME: FROM THE LATE ORDOVICIAN RICHMONDIAN INVASION TO PHANEROZOIC ECOSYSTEM REVOLUTIONS (Invited Presentation)

Throughout the Phanerozoic, several major revolutions have occurred in benthic marine ecosystems as a result of notable shifts of faunal dominance in benthic marine communities, such as the Great Ordovician Biodiversification Event (GOBE) and the Mesozoic Marine Revolution (MMR). These events are characterized by increasing ecospace utilization, predation intensity, motility, infaunality, and disturbance and suggest that ecological complexity has increased through geologic time as specialized morphologies and functions have evolved. Here we employ a novel approach to examining the evolution of metazoan marine ecosystems using food webs and functional diversity.

We first examined food web structure and functioning in shallow marine paleocommunities during the Late Ordovician (Katian) from the Cincinnati Series (USA), to determine whether ecosystem structure and functioning changed in response to a regional event, the Richmondian Invasion. We then examined potential changes across the Phanerozoic, using 11 additional paleocommunities. Food webs were categorized using descriptive metrics and cascading extinction on graphs models to explore structure, functioning and stability across the Richmondian Invasion. We found that despite similarities in overall structure the invasion resulted in several changes in ecosystem dynamics which led to decreased stability, such as a loss of functional groups, and that invaders replaced incumbents and filled preexisting niche space. Changes in food web structure were not restricted to regional scales, and changes also occurred across the Phanerozoic. Functional diversity, the evolution of new modes of life, increased from the Cambrian to Recent, a trend which became more pronounced when employing methods that take into account body size, a fundamental property relating to increasing energetics and metabolic ramping up.

We conclude that marine ecosystems from the Cambrian to today are fundamentally different, and that changes in ecosystem properties such as nutrient cycling, productivity, and the intensity or number of interactions among species and between trophic levels have occurred in response to regional events, such as invasions, and on a global scale as ecosystems increased in complexity.