View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002and diversity overall remained stable, even ifextinction was concentrated in short-term eventsor an event at the end of the interval.Estimating Overall Diversity of Predators.—Now let’s attempt to determine the diversity ofpredators through the Phanerozoic. Several factorsneed to be considered in estimating overall predatordiversity. The data on genera in the database aregrouped at the order level and above, but not allmembers of every higher taxon are exclusivelypredators or not predators. Not only that, buttrophic activity is not known for many seldomencounteredtaxa. I ignored the rare exceptions ingroups whose natural history is well known andthat are overwhelmingly predators or not predators(whale sharks are functionally filter-feeders, but theyare a minuscule portion of chondrichthyan genera)and designated those groups as entirely predatorsor non-predators. For groups that have a mixture ofpredators and non-predator members I determinedfrom descriptions of feeding habits and diet in theliterature (Parker, 1982 and other references as notedbelow in notes on individual taxa) approximatelyhow many taxa in each group seem to bepredominantly predators and, since these numberswere usually at the family level and some were“educated guesses,” I calculated a reasonable rangeof the proportion of taxa in each group that mightbe considered predators. This range is my estimateof what might be thought of as a confidence intervalconcerning the completeness and reliability of thedata available to a single experienced worker. I hopeit is clear that it frames a range of estimation; thebounds are not precisely determined. Future work,especially thoughtful compilations by specialists,will undoubtedly improve our knowledge. Theminimum proportion is the proportion of the taxain the group certain to be predators; the maximumproportion is the maximum proportion of the taxain the group that reasonably might be predators.Some more information on criteria is given withthe discussions of each major group below.Table 1 lists the taxa and the minimum andmaximum proportions chosen in estimating thediversity of predators. The proportions were thenused to determine the number of genera in eachgroup likely to have been predators in each timeinterval. Both maximum and minimum numberswere calculated, plus turnover. All groups weresummed together to get the total diversity range.The range of boundary-crossing diversity plus theturnover for the maximum reasonable diversity forall groups together are shown in Figure 2. Toestimate the average diversity of predators, theFIGURE 2—The range in number of boundary-crossing genera for estimated minimum and maximumnumbers of predators through the Phanerozoic. Turnover in the estimated maximum number of predatorsis also shown (the turnover for the minimum number would always fall inside that of the maximum).324