ENVIRONMENTAL CHANGE DROVE RATES OF PREDATION IN CARIBBEAN NEOGENE MOLLUSCAN COMMUNITIES

Predation is an important evolutionary force that has varied greatly in geologic history for reasons that are poorly understood. Ecological theory suggests that predation intensity should be positively correlated with primary productivity. We tested this productivity hypothesis by comparing the incidence of gastropod drill predation in over 100,000 bivalve shells before and after the collapse in Caribbean planktonic productivity 4-3 Ma due to the closure of the Central American Seaway. Contrary to expectation, the frequency of drilled shells doubled after productivity declined while the ratio of predator to prey abundance remained unchanged. The explanation lies in the several fold increase in shallow-water coral reef and seagrass habitats where predation intensity is much higher than in previously dominant soft-sediment environments. The ultimate ecological consequences of environmental change depend as much upon the cascading series of ecological interactions set off by the new conditions as the kinds and magnitude of the initial change.