A Potential Nutritional Basis for Resource Partitioning by Desert Rodents

Abstract

-Food-selection experiments were conducted in the laboratory with kangaroo rats (Dipodomys panamintinus), pocket mice (Perognathus parvus) and deer mice (Peromyscus maniculatus). Seeds of two species native to the site where rodents were trapped were used in the experiments. Bitterbrush (Purshia tridentata) has high-fat, high-protein seeds; Indian ricegrass (Oryzopsis hymenoides) is high in carbohydrate. When they were not under water stress, kangaroo rats ate Indian ricegrass almost exclusively, pocket mice ate equal amounts of bitterbrush and Indian ricegrass, and deer mice preferred bitterbrush seeds. When given bitterbrush as the sole seed source, with lettuce as a water source, kangaroo rats maintained body mass and increased their consumption of bitterbrush over four days. Differences among rodent species in seed preferences may be explained by morphological constraints on seed handling, differential sensitivity to toxic secondary compounds in bitterbrush or different nutritional requirements.