Is differential use of Juniperus monosperma by small ruminants driven by terpenoid concentration

TitleIs differential use of Juniperus monosperma by small ruminants driven by terpenoid concentration
Publication TypeJournal Article
Year of Publication2014
AuthorsEstell RE, Utsumi S.A., Cibils AF, Anderson D.M.
JournalJournal of Chemical Ecology
Start Page285
Date Published02/2014
ARIS Log Number297532
Keywordsgoats, herbivory, one-seed juniper, Oxygenated terpenes, Resource availability hypothesis, sheep, targeted grazing, terpenes

We examined the relationship between volatile plant secondary metabolite concentrations and Juniperus monosperma herbivory by small ruminants. Two groups of animals (10 goats or 5 goats plus 4 sheep) browsed 16 paddocks (20 x 30 m) containing one-seed juniper for six days during two seasons. Juniper leaves were sampled from 311 saplings on the same day they were browsed. Saplings were categorized by size (short [< 0.5 m], medium [0.5-1.0 m] or tall [> 1.0 m]) and browsing intensity (light [< 33%], moderate [33-66%] or heavy [> 66%]). Juniper bark was also collected from 12 saplings during spring. Total estimated terpenoid concentrations in leaves and bark were 18.3 ± 0.3 and 8.9 ± 0.8 mg/g, respectively, and the dominant terpene in both tissues was a-pinene (11.1 ± 0.2 and 7.6 ± 0.7 mg/g, respectively). Total terpenoid concentration was greater (P < 0.001) in spring than summer (20.6 ± 0.5 vs. 16.7 ± 0.3 mg/g, respectively) and lower (P < 0.001) in short saplings than medium or tall saplings (16.5 ± 0.6 vs. 19.8 ± 0.4 and 19.5 ± 0.4 mg/g, respectively). Total concentration also differed (P < 0.001) among the three defoliation categories (16.1 ± 0.4, 18.7 ± 0.5, and 21.2 ± 0.6 mg/g for heavy, moderate, and light, respectively). The smallest subset of terpenes able to discriminate (P < 0.001) between heavy and light browsing intensity categories included eight compounds ([E]-ß-farnesene, bornyl acetate, '-eudesmol, endo-fenchyl acetate, y-cadinene, a-pinene, cis-piperitol, and cis-p-menth-2-en-1-ol).