title: Grizzly bear predation links the loss of native trout to the demography of migratory elk in Yellowstone.
abstract: The loss of aquatic subsidies such as spawning salmonids is known to threaten a number of terrestrial predators, but the effects on alternative prey species are poorly understood. At the heart of the Greater Yellowstone ecosystem, an invasion of lake trout has driven a dramatic decline of native cutthroat trout that migrate up the shallow tributaries of Yellowstone Lake to spawn each spring. We explore whether this decline has amplified the effect of a generalist consumer, the grizzly bear, on populations of migratory elk that summer inside Yellowstone National Park (YNP). Recent studies of bear diets and elk populations indicate that the decline in cutthroat trout has contributed to increased predation by grizzly bears on the calves of migratory elk. Additionally, a demographic model that incorporates the increase in predation suggests that the magnitude of this diet shift has been sufficient to reduce elk calf recruitment (4-16%) and population growth (2-11%). The disruption of this aquatic-terrestrial linkage could permanently alter native species interactions in YNP. Although many recent ecological changes in YNP have been attributed to the recovery of large carnivores--particularly wolves--our work highlights a growing role of human impacts on the foraging behaviour of grizzly bears.
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA. arthur.middleton@yale.edu
authors.forename: Arthur D
authors.initials: AD
authors.lastname: Middleton
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Morrison
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Fortin
authors.forename: Charles T
authors.initials: CT
authors.lastname: Robbins
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Proffitt
authors.forename: P J
authors.initials: PJ
authors.lastname: White
authors.forename: Douglas E
authors.initials: DE
authors.lastname: McWhirter
authors.forename: Todd M
authors.initials: TM
authors.lastname: Koel
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Brimeyer
authors.forename: W Sue
authors.initials: WS
authors.lastname: Fairbanks
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Kauffman
mesh_terms: D000818:Animals; D003670:Deer / Q000502:physiology*; D003710:Demography; D005260:Female; D020387:Food Chain; D058865:Introduced Species; D008297:Male; D011157:Population Dynamics; D011235:Predatory Behavior; D012621:Seasons; D014337:Trout / Q000502:physiology*; D001503:Ursidae / Q000502:physiology*; D014959:Wyoming
keywords: aquatic subsidies; cutthroat trout; elk; grizzly bears; invasive species; lake trout