The way forward

A number of common themes run throughout this volume. First, one begins to appreciate just how much variation there is in body size among most groups of animals. For the most part, a clade is not a homogenous collection of similar bauplans. Even among volant taxa, such as birds and bats, substantial variation in body mass exists despite the considerable constraints imposed by fl ight (chaps. 3, 4, 8). Moreover, body size variation is clearly important in terms of community and ecosystem dynamics and structure (e.g., chaps. 6–9); how animals interact with their environment is strongly mediated by their body mass. Thus, the size of an organism is of great physiological and ecological signifi cance (Peters 1983). Second, there are remarkably consistent patterns in the body size distributions of some taxa across spatial and temporal gradients that may well refl ect how organisms acquire and allocate energy. For example, right-skewed body size distributions seem to be quite common among diverse clades (chaps. 1–5). However, these regular patterns vary between groups in ways that we do not yet understand. As Maurer and Marquet (chap. 7) note, numerous processes have been invoked to explain the minimum, maximum, mode, and shape of body mass distributions. Which of these processes are universal? Which are unique to particular taxa or geological histories (e.g., response to glaciation; chap. 2)? Are size frequency distributions similarly skewed to the right because organisms contributing to these distributions share similar trophic or life history traits? To some extent, our inability to develop universal explanations may refl ect a lack of fundamental information. For example, as Gaston and Chown (chap. 1) note, it is likely that only 9%–24% of