Calow (1983) realized that differences between parasites and their free-living relatives can be explained by the differences in nutrient richness. I propose a model that is based on Calow's idea which identifies the relative position of different trophic strategies (e.g. predation, grazing, parasitism and others) based on (1) the differences by which consumers arrive at their intrinsic rate of growth, and (2) the ecological impact they inflict on their hosts. I hypothesize that trophic interactions can be clarified if a parameter is included that takes into account the host's/prey's fate in the interaction. Moreover, this model suggests specific trophic evolutionary pathways (TEPs) between each strategy, and suggests that some pathways are more likely than others. In particular, parasitoidism is believed to be a highly derived strategy, and the TEPs presented in the model suggest parasitoidism could have arisen from either a predator-like or a typical-parasitic ancestor. Though the trophic categories determined by the model seem intuitive, this approach does provide, apparently for the first time, an objective, mathematically and ecologically useful basis for classifying animal trophic relationships. / Graduation date: 1998