Analyzing body size as a factor in ecology and evolution

An organism's size is perhaps its most apparent characteristic. The recent outpouring of studies on the influence of body size on all aspects of biology and evolution and the extension of the focus of such studies from physiology and functional morphology to ecological characteristics has resulted in a spate of books on the subject (17, 82, 99). As a result, the field of scaling, the study of the influence of body size on form and function, has rather suddenly become a prominent focus in ecology and evolutionary biology. [I prefer Schmidt-Nielsen's (99) term of "scaling" for this field over Gould's (35) "allometry," since the latter refers also to departures from geometric similarity; confusion of the two senses of "allometry" has further complicated an already confused literature.] Because the study of body size was long relegated to a minor position in biology, standards within the field have tended to be lax and the literature is replete with papers of dubious methodology, analysis, and conclusions.
Inappropriate comparison of different types of data is probably the most common error in the scaling literature (e.g. 42, 73); data plots often treat individuals and species as equivalent entities. Less obvious but just as erroneous is the common tendency to equate intraspecific trends with ontogenetic or evolutionary phenomena. In scaling studies, both the level of analysis and the kinds of data included must be carefully chosen if the results are to be meaningful. See Cock (22) for a clear and careful introduction to this topic.