Q. Such complications forced this overly simplistic scheme to give way in 1975, when late Frank H. Rigler, a zoologist at University of Toronto, published an influential critique of concept. It was n that William E. Odum (of University of Virginia's Department of Environmental Sciences) and Eric J. Heald (of University of Miami"s Rosenstiel School of Marine and Atmospheric Sciences) pointed out that more precise estimates of trophic level could be obtained from actual observations of diet. ir advance, as followed in current practice, treats trophic level as an empirically determinable property of a species like average size or metabolic rate. So explain how exactly do marine biologists estimate trophic level for a given species?