View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002colonial animals in a manner similar to the grazingof herbivores on vegetation, suspension-feedingand deposit-feeding animals that may consume tinyplanktonic or interstitial animals as part of theirintake of food, but do not pursue animals asindividual targets, and parasites that may weakentheir hosts, but do not actively subdue and kill themin order to gain their nutrition, are not regarded aspredators in the sense meant by the definition usedhere. Predators, then, are secondary consumers—heterotrophs higher in the food chain than primaryproducers (autotrophs), primary consumers(herbivores), “indeterminate” level consumers(deposit feeders, consumers of microbes anduseable dead organic material from many sources,and suspension-feeders, organisms that also gainsustenance from mixed low levels of the foodchain—phytoplankton and/or animal plankton), orcarnivores that are either purely scavengers or eatentirely passive prey that is as available asvegetation is to herbivores.One implication of restricting the definition ofpredators to metazoans catching other metazoansis that the nature of the food pyramid restricts theabundance of predators. While the relationships arevery complex (May, 1981; Pollis and Winemiller,1996), the biomass of predators is alwaysconsiderably less than that of prey. Although acommon “rule of thumb” is that each level of afood pyramid contains only about ten percent ofthe biomass of the next lowest level, therelationship is, in fact, highly variable. Calculatedvalues of food-chain efficiencies vary from lessthan 0.1% to over 10% (May, 1981).In this paper I use the unpublished database ofthe stratigraphic ranges of genera of marine animalscompiled by the late J. John Sepkoski, Jr. to estimatethe genus diversity of marine metazoan predatorsboth as a group and within many of the major taxathat contain predators. The data are necessarilylimited to taxon richness only, not abundance, so nodiversity metrics that account for the interaction ofabundance and taxon richness are used. But taxonrichness alone does have implications for predatorpreyrelationships. Because the abundance ofpredators must be less than prey (from a factor of0.3 to less than 0.001), we can extrapolate that,unless contravening major secular changes occur inthe average abundance of individual predatorspecies, changes in diversity of predator taxaprobably reflect changes in the abundance of preytaxa. It would be unlikely, at least, that predatordiversity would increase in the face of decreasingbiomass (abundance) of prey. This will be discussedin more detail in later parts of the paper.The groups designated in this paper as prey taxaare restricted to non-predators only. Some predatorsprey on other predators. Although those preyed-uponpredators are themselves prey, they are not countedin the prey groups in the examples in this paper. Butthe inclusion of some predators as prey would extendfood chains and expand the trophic pyramid forpredators even more than in the case consideredhere, only adding to the increase, documented inthis paper, of non-predatory prey alone—thus furthersupporting, not countering, most of the conclusionsof the paper.Tracking Genus Diversity.—Figure 1 illustratesthe history of genus diversity of metazoa throughthe Phanerozoic. Because the metazoa compriseover 90% of the taxonomic richness tabulated incomprehensive synoptic databases on marinediversity, the metazoan diversity path follows thewell-known pattern established in the “consensuspaper” of Sepkoski et al. (1981) and best knownfrom the widely reproduced family diversity curve(Sepkoski, 1981). In the Paleozoic we see the“Cambrian Explosion” (the increase in diversityin the Early Cambrian), the Cambrian “Plateau,”the Ordovician Radiation, and the long interval(starting in the Caradocian) of fluctuating but nontrendingdiversity that lasts until the Late Permian.Diversity changes during the “Paleozoic Plateau”include the end-Ordovician mass extinction,diversity buildup through the Silurian and EarlyDevonian to a Mid-Devonian peak, followed by along slide in diversity through much of the Middleas well as the entire Late Devonian, recovery ofdiversity in the early part of the Carboniferous andthen fairly stable diversity through the rest of theCarboniferous and the first half of the Permian.The Paleozoic ends with the precipitous drop of320