Of course it is one thing to develop a semantic framework and judge the state of knowledge of ecological versatility in these terms (Chapters 2 and 3), but quite another to begin to understand or explain the evident variation in versatility that we see in nature. I think that the differences in the quality of studies revealed by the survey are related rather directly to the variety of ecological mechanisms involved and also to taxonomic characteristics. Thus, the importance of constraints (e.g., allelochemicals) on resource use emerged as a key issue in studies involving plants and their herbivores, as did aspects of fitness, which were seen as fundamental measures of plant responses to resource availability. Neither aspect was as well studied by ornithologists or mammalogists. On the other hand, in taxa in which populations are differentiated in an obvious way, such as many species of Anolis and the sticklebacks of Delbeek and Williams (1987), data often were collected in such a way as to allow the intrapopulational differences in versatility to be gauged. In species in which differentiation is less obvious, data for individuals often were pooled together with little regard. Thus, differences in the way in which studies of resource use are done seem to depend upon: (1) the apparency or ‘obviousness’ of possible factors, which depends upon processes and taxonomy; (2) the difficulty of measurement; and (3) (almost certainly) the cultural norms and channelized thinking of each ecological subdiscipline (e.g., herbivory, predation, polymorphism).