Belowground Herbivory: The Adaptive Geometry of Geomyid Burrows

Abstract

An analysis of the relationship between the energy costs and benefits of belowground herbivory is undertaken for the rodent family Geomyidae. Given that geomyids attempt to maximize the net energy gain per segment of burrow excavated for habitats featuring a uniform horizontal and unimodal vertical component of the dispersion pattern of belowground plant biomass a unique combination of burrow radius, depth and segment length is optimal. If geomyids are attempting to maximize the net gain per unit volume of soil excavated, burrow radius and segment length sould be as close to 0 as possible. Burrow geometry indicates that burrow radius is as small as possible; segment length may not be. This paradox can be resolved if it is assumed that burrowing costs rise dramatically for burrows with diameters larger than just necessary for free passage. Environments promoting one or the other of the energy maximization strategies will then lead to differences in body sizes, a widely observed phenomenon among geomyid species and populations.