METABOLIC COSTS OF RODENTS FEEDING ON PLANT-CHEMICAL DEFENSES - A COMPARISON BETWEEN AN HERBIVORE AND AN OMNIVORE

We analysed the combined effect of subchronic dietary cellulose and ta nnic acid on the metabolic cost in the herbivorous burrowing caviomorp h rodent Octodon degus, and the omnivorous Sigmodontine Phyllotis darw ini. Both are sympatric rodent species living in open scrub subjected to summer droughts in the Mediterranean communities of northern and ce ntral Chile. We measured basal metabolic rate (BMR), maximum metabolic rate of thermoregulation (MMR) and the aerobic scope. As a consequenc e of the ingestion of comparative higher concentrations of dietary tan nic acid and fiber, a higher MMR was observed in P. darwini than in th e herbivorous O. degus. Metabolic costs were observed under maximal bu t not under basal conditions. (C) 1997 Elsevier Science Inc.