ENTERING THE CONSUMER AGE: PREDATION, HERBIVORY, OXYGEN, AND PHANEROZOIC ECOSYSTEMS

The Phanerozoic eon is marked by several increases in the evolutionary and ecological role that consumers — animals that eat other living organisms — play in ecosystems. Multicellular predation was initiated during the latest Proterozoic, as indicated by complete and incomplete drill-holes and by repaired injuries in prey. Subsequent events in predation led to increases in the sizes of prey taken and in the speed with which prey are subdued. Multicellular herbivory was at first rare in the sea as well as on land, but increased in intensity and in the extent to which plant tissues were mechanically broken up before ingestion. Predation and herbivory have the effect of increasing the speed of nutrient cycling in ecosystems, because death of the food is no longer a precondition for the flow of nutrients from victim to consumer. Models imply that the resulting rise in productivity stimulates intensification of predation and herbivory. As a result, top-down evolutionary and ecological control by consumers has become an increasingly dominant theme in Phanerozoic ecosystems over time. On a much shorter time scale, a very similar sequence of events has occurred in human economic history. Times of increasing temperature, expanding areas of productive habitat, and rising oxygen levels in the biosphere may have been particularly important for the evolution of physiologies and organic designs that made exploitation of living resources faster and more widespread.