View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 20021994). How do connections among multiplepopulations affect the processes shaping theevolution of interactions among species? Byidentifying general patterns, we can betterunderstand the constraints that interactions imposeon the evolution of organisms. In addition, if shorttermreciprocal adaptation (via inducibility) betweenpredator and prey is a common process, then preyare likely to exert some selective pressure on theirpredators over the short term (and perhaps in specificcases over the long term; see above).At ecological time scales, reciprocal adaptationis likely to occur (Thompson, 1999b); coevolutionmay also characterize the long-term evolution ofspecific predator-prey systems. However, at thelargest scale of paleontological study, the escalationhypothesis may be the most important descriptionof the evolutionary process (see also Thompson,1999b). Over the long run, then, we believe, it islikely that predators control the overall directionalityin evolution (i.e., evolutionary megatrajectories)because of the inequality of predator and prey incontrol of resources (Vermeij, 1999, 2002). Predatorsof large effect influence community structure byway of their high rates of consumption and theirgeneralized diets (Virnstein, 1977; Peterson, 1979;Paine, 1980; Hines et al., 1990; Birkeland, 1996),and likely are “chiefly responsible for organizingthe economy, for defining the roles and attributesof the entities with which they interact, and forsetting the course of economic change” within thecommunity (Vermeij, 1999, p. 247).The fundamental question raised in theintroduction was whether there are any general“rules” that govern the ecological and evolutionarytrajectories and outcomes of interactions (see alsoHerre, 1999). In order to address this question, wemust recognize that predator-prey interactions arecomplex systems and that multiple factors mayinfluence the outcome of encounters betweenpredator and prey. Thus “it is important tounderstand the interactions among several differenttypes of species in order to provide the context toproperly pose and test evolutionary hypothesesabout any of them” (Herre, 1999, p. 235). Onceother agents of selection are considered, theintuitive expectation of the type of arms racedriving the evolution of a species interaction isoften called into question. Thus it is important toview any predator-prey system within the contextof the other species that may influence theinteraction, and to clearly understand the functionalinterrelationships among them. We have not cometo any firm conclusions on the “rules” governingthe processes of coevolution and escalation in anyspecific predator-prey interaction because in manysystems the question is still open. This does notimply that the governing “rules” that yieldexplanatory power concerning the outcomes ofspecies interactions and their long-term effects inevolution are not important. Instead, as Herre (1999,p. 236) pointed out, “understanding why the ruleswork in the cases that they do is crucial, as is theappreciation that context and scale determine theapplicability of those rules we presently recognize.”Distinction between escalation and coevolution canmost reliably be achieved with carefuldocumentation of the details of the natural historyof different systems (Vermeij, 1994). As Kohn(1989, p. 1095) eloquently stated: “Natural history,in focusing on the individual whole organism in itsenvironment, occupies a central position in thespectra of spatial and temporal scales appropriateto biological science.” Solutions to the conceptualconflicts between the coevolution and escalationprocesses fundamentally depend on growingcollaboration among ecologists and paleontologists.This collaboration remains an attractive butseemingly elusive goal; but with it will come amuch deeper understanding of the processes thathave shaped and continue to shape the evolutionof predator-prey systems.ACKNOWLEDGMENTSThis work was supported in part by a pilotproject grant from the Center for Marine Scienceat the University of North Carolina at Wilmington.We thank R. K. Bambach and J. A. Rice for helpfulreviews and G. S. Herbert and G. J. Vermeij forvaluable discussion. This is ContributionNumber269 of the Center for Marine Science.370