View - Kowalewski, M. - Virginia Tech

BAMBACH—SUPPORTING PREDATORSSUPPORTING PREDATORS: CHANGES IN THEGLOBAL ECOSYSTEM INFERRED FROM CHANGES INPREDATOR DIVERSITYRICHARD K. BAMBACHProfessor Emeritus, Virginia Tech;Botanical Museum, Harvard University, 26 Oxford Street, Cambridge, MA 02138 USAABSTRACT—This paper presents new estimates of the genus diversity of predators in each major taxon containingpredators, as well as an estimate of the total genus diversity of predators through the Phanerozoic. Predatorshave never been numerically abundant compared to prey. However, the diversity of predators and the proportionof total faunal diversity composed of predators have both increased over time, implying that ecosystems haveincreased their ability to support either more predators or more specialization among predators. Also, turnoverin diversity dominance among predator groups, with more energetic predator taxa replacing or being added to afauna of less energetic groups, implies that the energy available in marine food webs has increased. The apparentincrease in diversity and biomass of primary producers plus patterns of diversity change in prey taxa supportsthese inferences based on patterns of change in predators alone.INTRODUCTIONTHIS PAPER COMPILES estimates of theglobal genus diversity of marine predators aspreserved in the fossil record through thePhanerozoic. The global picture is the sum of localand regional distributions. No local ecosystem needhave the same relative pattern of either taxonrichness or abundance as the global whole. Butchanges in global patterns can only occur throughthe accumulation of changes in local or regionalpatterns. Therefore, determining pattern, andchange in pattern, at the global level not only givesus information on the history of life in sum, a notuninteresting subject (consider, for example, theamount of attention given mass extinctions), butalso identifies times when change must have beenoccurring at the local or regional level. Globalanalyses may not reveal the detailed story ofchanges in organism-organism interactions in eachlocal setting, but global analyses provide invaluableindices of when local changes must have beenoccurring. They serve as a guide to the timeintervals for which targeted research at local orregional levels could have large dividends.Defining predator.—What do we mean by theterm predator? The American Heritage Dictionaryof the English Language, Third Edition(Soukhanov, 1992) defines predator as “anorganism that lives by preying on other organisms.”Even though preying can be interpreted to meancatching and killing, the definition as stated is toobroad for the sense commonly used by biologists(and used in this paper) because it would includeherbivores, parasites, and suspension feeders aswell as deposit-feeders that gain sustenance frommicrobes. Nor is predation, as used here, simplysynonymous with carnivory (which includesscavenging and some forms of suspension-feeding,such as the feeding of baleen whales). Predation(as used here) and these other trophic systems mayall be mathematically roughly equivalent activitiesin terms of energy acquisition or in their effects onthe populations of the organisms preyed upon, butthe other activities don’t catch the sense ofspecifying those organisms that hunt or trap,subdue, and kill individual animals that have somecapacity for either protection or escape. This latterrestricted categorization is what I mean by the termpredator. Organisms that “graze” on non-motile319