Abstract

Bradley succeeded in conceptualizing biological productivity in terms—monetary investment vs. profit—that could be applied to organisms as different in form and habitat as trees, grapevines, and crayfish.41 This form of measurement was not precise enough to have served as a basis for actual comparisons of production rate. His way of thinking, however, could have been applied with other terms of measurement once the usefulness of such measurements had been realized. The realization that production rate is an important factor is implicit in his discussions, but for his purposes, yearly yields were generally sufficiently precise determinations.Although Bradley drew substantially upon the contributions of others, his writings represent a significant beginning for productivity ecology. All of the kinds of investigations that he reported could have been extended, rendered more precise, and formed the basis of ecological generalizations during the eighteenth century.There were, however, certain conceptual limitations imposed by a lack of relevant knowledge in physiology and in physical science. A good understanding of productivity ultimately depends upon an understanding of metabolism, which in turn depends upon an understanding of photosynthesis, respiration, biochemistry, and the first and second laws of thermodynamics. The essential knowledge of these subjects would not be available until decades after Bradley's time