Why is intraspecific niche partitioning more common in snakes than in lizards?

Introduction, The scientific literature on foraging biology in lizards has tended to ignore intraspecific variation. Thus, the species is treated as the unit of analysis, under the implicit assumption that variation within a single species (and, to an even greater degree, within a single population) is trivial relative to variation among species. Many authors therefore talk of broad phylogenetic patterns in foraging mode, with all taxa within major lineages placed within the same major category (e.g. active or ambush). Such generalizations may have substantial value in pursuing broad issues, but at the population level they are simply wrong for many types of organism. Groups of related species certainly share many distinctive features of foraging biology, and there is a genuine validity to statements about lineage-wide patterns. None the less, a detailed analysis of almost any single population (let alone one species) is likely to reveal diversity in trophic biology. For example, juveniles may feed in different ways, in different places and on different kinds and sizes of prey than do adults within the same population. Similarly, males and females may differ in prey utilization. For several reasons, snakes offer more dramatic examples of such intraspecific niche divergence than do lizards. In this chapter, we review published evidence for size and sex effects on foraging biology in snakes, consider underlying biological factors that generate such diversity, and attempt to explain why snakes and lizards – two very closely related groups of organisms – differ so dramatically in the occurrence of intraspecific niche partitioning.