View - Kowalewski, M. - Virginia Tech

VERMEIJ—EVOLUTION IN THE CONSUMER AGELeonard et al., 1999; for a general review ofinduced phenotypes see Agrawal, 2001).These important findings suggest that predatorand prey influence the directions of each other’sevolution. At first, adaptation is non-genetic, thanksto a responsiveness of behavior and morphologyto environmental cues. Responsiveness is undergenetic control, but the responses themselves takeplace over the short term within an individual’slifetime without genetic instruction. Extremelyrapid—in fact, almost instantaneous—reciprocaladaptation between predator and prey thusproceeds on timescales commensurate withindividual lifespans, but in the long run, predatorand prey evolve by a process of escalation(Vermeij, 1987)—a genetically based evolutionaryprocess in which predators retain the evolutionaryand economic edge of control over the prey. Withthe evolution of predators, therefore, the biospheretruly entered the consumer age.INFERENCES OF PREDATIONIN THE PASTTwo principal types of data are potentiallyinformative about the evolutionary role thatpredators have played in the past. These are (1)traces of predation, successful and especiallyunsuccessful attacks as chronicled by marks lefton fossils; and (2) functional-morphologicalinferences of predatory performance andantipredatory defense drawn from observations andexperiments on living predators and their prey.Repaired injuries provide direct evidence thatthe organism bearing them withstood significanttrauma, often inflicted by competitors andpredators. The incidence of such repairs in a preypopulation depends on (1) the probability of beingattacked, and (2) the probability that the attack isunsuccessful from the predator’s point of view. Theprobability of attack depends on the number ofpredators and on the prey’s age and lifespan,whereas the probability of failure is a function ofthe size of the predator relative to that of the prey.In general, the proportion of attacks that fail fromthe predator’s perspective should increase withprey size and age, although exceptions are knownamong crabs attacking snails (Vermeij, 1982b). Thelonger a potential victim lives, the more injuries itis likely to accumulate.For nonclonal organisms, such as manyanimals, the only form of predation that leavesreliable indicators of both successful andunsuccessful attacks is drilling. For predationinvolving skeletal breakage, we have reliable dataonly on unsuccessful attacks that are subsequentlyrepaired and that are preserved on a part of theskeleton that we can observe.Broken fragments are abundant in the fossilrecord, and no doubt in part reflect the work ofsuccessful predators. Cadée (1994), for example,made careful observations showing that most of thefragments of molluscan shells in the Wadden Sea(the Netherlands) are the result of predation by gullsand ducks. Merle (2000) inferred the destructiveaction of a large stingray from two largereconstructed early Eocene shells found as fragmentspreserved close together in sediments that indicatequiet-water conditions and rapid sedimentation.I have similarly argued from the types of lethaldamage done by crabs and spiny lobsters that thevast majority of lethally broken shells on modernseashores indicate successful predation (Vermeij,1982b). Holes in fossil shells comparable to thedamage done today by shell-smashing mantisshrimps (stomatopods) may indicate the work ofthese predators as argued by Geary et al. (1991)for the Plio-Pleistocene of Florida, Pether (1995)for shells from the Holocene of southern Africa,and by Baluk and Radwanski (1996) for snails inthe middle Miocene Korytnica Clay of Poland.Similarly, Boyd and Newell (1972) suggested thatmany of the fragments they encountered in Permiansediments in Wyoming chronicled predatorysuccesses. The problem is, of course, that countingsuch fragments is fraught with taphonomicinterference. It is difficult to distinguish betweensharp-edged fragments produced by shell-breakersand similar fragmentation produced by compactionor other diagenetic effects. Moreover, smaller preywould be so thoroughly macerated that diagnosticremains may not be preserved or recognizable.379