Population Ecology of Desert Rodent Communities: Body Size and Seed‐Husking as Bases for Heteromyid Coexistence

Abstract

Seven species of heteromyid rodents varying in size from 8 to 114 g were studied in the laboratory. Starved rodents husked four kinds of large seeds (spinach, sunflower, squash and pumpkin) and were timed at the task. Geometric mean husking times varied from 3.1 to 70.1 seconds, depending on the seed and the rodent. Husking time was inversely proportional to an animal's body size. However, despite their slowness, smaller animals appear to be more efficient at dealing with these large seeds because they have a smaller metabolic drain. This conclusion is based on the assumption that gross caloric need increases linearly with (body weight).75. The authors defend the assumption and thus believe that smaller animals have a competitive advantage while husking seeds. These rodents might engage in a limited amount of habitat and resource selection based on their relative seed—husking abilities. However, the order in which the various species should prefer these seeds is quite similar, so resource allocation based on husking speed differences would seem of little potential importance in maintaining competing heteromyids in a state of coexistence. Previous investigators have shown that seed selection occurs in some cases, but many cases are also known in which little or no selection is practiced.