The scale-precision trade-off in spacial resource foraging by plants: restoring perspective

From the results of a comparative study using quantitative standardized assays of the scale and precision of responses of root and shoot systems to resource patchiness, Campbell et al. (1991; Oecologia 87: 532-538) proposed a mechanism of species coexistence in herbaceous communities involving a dynamic equilibrium between, respectively, the coarse- and fine-scale foraging of dominant and subordinate species. The purpose of this paper is to reject a recent assertion that with respect to root systems the scale-precision hypothesis has been falsified.

Reference to the original papers confirms that the scope of the hypothesis was confined to circumstances (eg. mown meadows) where the vigour of potential dominants is restricted by intermittent removal of biomass. This qualification in the original hypothesis is a crucial omission from the meta-analysis conducted by Kembel and Cahill (2005; American Naturalist 166: 216-230). The original papers also contain examples that illustrate the operation of forms of selection that prevent the development of precise foraging below ground; these also appear to have escaped the attention of recent participants in this field of research.