title: Spatial heterogeneity in the strength of plant-herbivore interactions under predation risk: the tale of bison foraging in wolf country.
abstract: Spatial heterogeneity in the strength of trophic interactions is a fundamental property of food web spatial dynamics. The feeding effort of herbivores should reflect adaptive decisions that only become rewarding when foraging gains exceed 1) the metabolic costs, 2) the missed opportunity costs of not foraging elsewhere, and 3) the foraging costs of anti-predator behaviour. Two aspects of these costs remain largely unexplored: the link between the strength of plant-herbivore interactions and the spatial scale of food-quality assessment, and the predator-prey spatial game. We modeled the foraging effort of free-ranging plains bison (Bison bison bison) in winter, within a mosaic of discrete meadows. Spatial patterns of bison herbivory were largely driven by a search for high net energy gains and, to a lesser degree, by the spatial game with grey wolves (Canis lupus). Bison decreased local feeding effort with increasing metabolic and missed opportunity costs. Bison herbivory was most consistent with a broad-scale assessment of food patch quality, i.e., bison grazed more intensively in patches with a low missed opportunity cost relative to other patches available in the landscape. Bison and wolves had a higher probability of using the same meadows than expected randomly. This co-occurrence indicates wolves are ahead in the spatial game they play with bison. Wolves influenced bison foraging at fine scale, as bison tended to consume less biomass at each feeding station when in meadows where the risk of a wolf's arrival was relatively high. Also, bison left more high-quality vegetation in large than small meadows. This behavior does not maximize their energy intake rate, but is consistent with bison playing a shell game with wolves. Our assessment of bison foraging in a natural setting clarifies the complex nature of plant-herbivore interactions under predation risk, and reveals how spatial patterns in herbivory emerge from multi-scale landscape heterogeneity.
authors.affiliation: Département de biologie and Centre d'étude de la Forêt; Université Laval, Québec, Québec, Canada.
authors.forename: Léa
authors.initials: L
authors.lastname: Harvey
authors.forename: Daniel
authors.initials: D
authors.lastname: Fortin
mesh_terms: D000818:Animals; D018533:Biomass; D016164:Bison / Q000502:physiology*; D017753:Ecosystem; D005247:Feeding Behavior; D020387:Food Chain; D060434:Herbivory; D008954:Models, Biological; D018521:Plant Physiological Phenomena; D011235:Predatory Behavior; D019596:Wolves / Q000502:physiology*
references.citation: J Theor Biol. 2009 Jan 21;256(2):187-200
references.pmid: 18952108
references.citation: Oecologia. 1995 Sep;104(1):39-44
references.pmid: 28306911
references.citation: Oecologia. 2003 Jan;134(2):219-27
references.pmid: 12647163
references.citation: Ecology. 2011 Dec;92(12):2258-66
references.pmid: 22352165
references.citation: Ecology. 2011 Jan;92(1):240-52
references.pmid: 21560694
references.citation: Am Nat. 1992 Nov;140 Suppl 1:S63-84
references.pmid: 19426027
references.citation: J Anim Ecol. 2008 May;77(3):439-47
references.pmid: 18248387
references.citation: Trends Ecol Evol. 2009 Mar;24(3):127-35
references.pmid: 19185386
references.citation: PLoS One. 2012;7(5):e37069
references.pmid: 22606328
references.citation: Theor Popul Biol. 1976 Apr;9(2):129-36
references.pmid: 1273796
references.citation: Oecologia. 2005 Sep;145(2):335-43
references.pmid: 15965755
references.citation: Theor Popul Biol. 2009 Aug;76(1):52-8
references.pmid: 19371755
references.citation: Ecol Appl. 1993 Aug;3(3):497-505
references.pmid: 27759250
references.citation: Ecology. 2010 Oct;91(10):2995-3007
references.pmid: 21058559
references.citation: Ecology. 2009 Sep;90(9):2480-90
references.pmid: 19769126