The Cost of Roaming Free: Assessing the Effects of Plant Secondary Metabolites on Diet Selection and Nutritional Condition in a Free-Ranging Generalist Herbivore

• Main Author: Melody, Daniel Patrick
• Format: Text
• Language: unknown
• Published: ScholarWorks 2017
• Subjects: herbivore; nutritional condition; glucuronic acid; moose; balsam fir; PSM detoxification; Integrative Biology; Population Biology; Alces alces
• Online Access: https://scholarworks.boisestate.edu/td/1349; https://doi.org/10.18122/B2QQ71; https://scholarworks.boisestate.edu/context/td/article/2425/viewcontent/Melody_Daniel_Patrick_thesis_December2017.pdf

Large vertebrate herbivores have a wide variety of browsing options available. However, most plants contain a suite of plant secondary metabolites (PSMs) that can have toxic effects when ingested. Herbivores must therefore make dietary choices that minimize the potentially harmful effects of PSM ingestion and maximize the use of available nutrients and protein. During winter months, in northern latitudes, climatological factors restrict browsing options and many populations of herbivores must subsist primarily on forage that is relatively poor in nutritional quality and high in PSMs. Many species of herbivores have developed a suite of behavioral and physiological adaptations to cope with increased PSM exposure, including selective foraging and increased detoxification efficiency of potentially harmful PSMs. However, detoxification of PSMs may be energetically costly, exacerbating the effects of winter nutritional deficits, which in turn further decreases nutritional condition of free-ranging populations. As a result, PSMs may directly influence diet selection and winter nutritional condition of free-ranging herbivores. We used moose (Alces alces) on Isle Royale National Park, Michigan, to test how PSMs influence the diet selection, rates of intake and the physiological consequences of diet selection in a large mammalian herbivore during winter. We identified browsing patches and bite marks on balsam fir (Abies balsamia) trees and examined the PSM chemical profile and protein content of browsed and unbrowsed trees. We found that both diet selection and rate of intake by moose was directly influenced by PSMs. However, environmental conditions (e.g. snow depth) were the primary governing factor of intake rate. We also examined the effect of PSMs on nutritional condition of island moose using urine collected from snow. We quantified the concentrations of three metabolites found in urine: Glucuronic Acid (GA) as a biomarker of PSM exposure, Urea Nitrogen (UN) as a biomarker of overall nutritional condition, and ...