Paper presented at the "Symposium on Ingestion of Poisonous Plants by Livestock," February 15, 1990, Reno, Nevada. A diverse array of secondary metabolites deters feeding by mammals on woody plants. However, not all secondary metabolites are equally deterrent and the potencies of these substances as antifeedants is related to their structures. Although the physiological reason underlying deterrence by secondary metabolites is not well understood, the available evidence indicates that toxicity is more important than digestion inhibition. Resource limitation influences the production of secondary metabolites by woody plants. Species that are adapted to unproductive habitats are more chemically defended than species that are adapted to productive habitats. Resource limitation also affects the phenotypic expression of chemical defense with nutrient stress favoring increased production of carbon-based secondary metabolites and reduced production of nitrogen-containing secondary metabolites. Light stress has the opposite effects on the production of these substances. Herbivory by mammals also affects the chemical defenses of woody plants. In some cases browsing results in increased defense and in others decreased defense. Three circumstances under which browsing by mammals can change the chemical defenses of woody plants are discussed. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020
Scholarly peer-reviewed articles published by the Society for Range Management. Access articles on a rolling-window basis from vol. 1, 1948 up to 5 years from the current year. Formerly Journal of Range Management (JRM). More recent content is available by subscription from SRM.