Antiherbivore Chemistry of Larrea Tridentata: Effects on Woodrat (Neotoma Lepida) Feeding and Nutrition

Abstract

During winter, creosote bush (Larrea tridentata) dominates the diet of desert woodrats (Neotoma lepida) in the California Mojave Desert. The stems and leaves of creosote foliage are coated with large quantities of phenolic resins (10—25% of dry mass). We investigated whether woodrats feeding on creosote were influenced behaviorally by the resin and whether ingestion of creosote resin reduced the digestibility of protein as hypothesized by Rhoades and Cates (1976). Preference trials demonstrated that woodrats consistently selected creosote plant parts of low resin content. Removal of the resin with diethyl ether ameliorated this feeding preference and increased overall palatability of creosote foliage. Addition of the resin to laboratory chow ration caused this food to be avoided also. When woodrats were fed rations of creosote foliage or resin—treated laboratory chow no reduction in protein digestibility occurred. However, dry matter intake was reduced when woodrats were fed chow containing 12% resin. Our results indicate that creosote resin does deter feeding by desert woodrats. The antiherbivore mechanism of creosote resin to desert woodrats is likely one of toxicity and not digestibility reduction. This toxicity may limit the amount of creosote foliage woodrats can consume, which would explain the winter body mass decline and mortality that we observed in woodrats on our study site. We discuss the impact plant defense chemistry may have had on the evolution of Neotoma in the southwestern deserts of North America.