Plant phenolics as chemical defenses: Effects of natural phenolics on survival and growth of prairie voles (Microtus ochrogaster).

Very few studies have shown experimentally that plant chemical defenses actually reduce the performance of individual mammalian herbivores, much less the density of mammalian populations. We investigated the effects of representatives of three classes of plant phenoiics on the survival and growth of prairie voles by incorporating the compounds into artificial diets and feeding them to weanlings for three weeks. At low levels of protein, both quercetin (a flavonoid) and tannic acid (a hydrolyzable tannin) caused reduced growth rates; no effect occurred at high levels of protein. Quebracho (a condensed tannin) inhibited feeding and thus was lethal at all levels of protein. These results indicate that plant phenolics are likely to influence the performance and dynamics of natural populations of microtine rodents by reducing the quality of available forage. The hypothesis that the primary mode of action of the phenoiics is the reduction of digestibility of protein was not supported. The reduced growth caused by both quercetin and tannic acid could be attributed primarily to their toxicity. The effect of quebracho resulted from reduced intake (unpalatability).