Foraging modes as suites of coadapted movement traits


William E. Cooper, Department of Biology, Indiana University-Purdue University Fort Wayne, Fort Wayne, IN 46805, USA. Tel: +1-260-481-6311; Fax: +1-260-481-6087


The nature and evolutionary bases of foraging modes remain uncertain despite intensive study. Whether species can be assigned to one of two foraging modes, ambush and active foraging, or to multiple modes, and whether modes exist or are extremes on continua of movements variables have been highly controversial. Bimodality of avian movements per minute (MPM) was claimed to support discreteness of modes, but lizards exhibit extensive unimodal variation. I present data for 58 lizard species on average speed (AS), speed while moving (MS), MPM and per cent time moving. Correlated evolution has occurred between the frequency, duration and speed of foraging movements, suggesting that these traits represent a coadapted suite of foraging movements. Cluster analysis using AS, MPM and per cent time moving assigned species to clusters isomorphic with traditional ambush and active foraging. Large empty regions in foraging space suggest that foraging modes represent adaptive peaks of suites of coevolved traits. All variables differed across clades and modes. Variation within taxa and modes suggests that historical and ecological factors determine modes. When MS replaces AS, four species change from ambush to the active cluster. Foraging modes are not fixed, discrete traits because substantial quantitative variation occurs within modes. All single movement variables are lognormally distributed, indicating that bimodality of single variables is not required for the existence of distinct foraging modes. As data on new taxa accumulate, gaps between clusters may be reduced and/or new modes identified. Currently, the two-mode paradigm remains appealing due to its broad explanatory power and simplicity.