Predator trophic guild assignment: The importance of the method of diet quantification

We quantitatively assessed the effect of three Methods of Diet Quantificati on (MDQ) (based on frequency of occurrence of prey, dry weight of prey rema ins, or estimation of fresh biomass ingested) on guild classification of th ree carnivores species based on five data sets. Diet dissimilarity matrices and recognition of trophic guilds were dependent on MDQ. Both omnivorous ( Red Fox, Vulpes vulpes, and Eurasian Badger, Meles meles) shifted to differ ent trophic guilds depending of the MDQ chosen, whereas Iberian Lynx (Lynx pardinus) remained consistently in the rabbit-eating guild. As a way to ass ess the pervasiveness of inconsistencies in guild classification, we applie d our approach to six other predator assemblages. The number of recognized guilds shifted as a result of MDQ in 4 of 6 comparisons, changes in guild m embership occurred in all assemblages, and mean percentage of guildmate fid elity was only 30 % (1SD = +/-21, n = 6). The choice of MDQ depends on the specific ecological question to be addressed with the data. When investigat ors focus on the effects of prey on predators, an estimate of biomass inges ted seems the best choice, but when the focus is on the effects of predator s on prey, an approach based on prey numbers is more appropriate.