RECONSTRUCTING PREDATION INTENSITIES FROM INJURIES: THEORETICAL AND PRACTICAL CONSIDERATIONS

Predation and its ecological and evolutionary consequences has been an important theme in paleobiology and its study in the fossil record has often focused on injuries. Although both biotic and abiotic factors may lead to injuries, those resulting from interactions with predators can often be recognized or inferred. Of special evolutionary importance are those injuries that are non-lethal because they are detrimental to a variety of physiological functions, their healing requires a substantial investment of energy, and thus they are likely to represent a strong agent of selection. The evolutionary impact of such non-lethal injuries is related to the rate at which they are produced, therefore determining the rate of the injury-producing process is of some interest. Commonly, data on injury frequencies have been employed as a proxy for this rate, and if injuries are shown as being a consequence of predation, this rate has been considered as equivalent to “predation intensity” or “predation pressure”. However, in a seminal work, Schoener (1979) showed theoretically that injury frequencies are not a function of the rate of such injury-producing events, but rather of the probability that such events are fatal. Here, this issue is revisited with a focus on ephemeral injuries, i.e. those that can heal completely and become unrecognizable, as is the case in many echinoderms. It is shown that for ephemeral injuries, the rate of injury-producing events can be reconstructed from injury frequencies if the time that it takes for an injury to heal is known. Two examples from echinoderms are used to illustrate how injury frequencies can be converted to a rate of the injury-producing events and how higher frequencies of injury need not correspond to higher rates of such events.