The distribution of deer biomass in North America supports the hypothesis of exploitation ecosystems


  • Crête

    1. Faune et Parcs, Service de la faune terrestre, 675, boul. René-Lévesque Est (BP 92), Québec, QC G1R 5V7, Canada.Université Laval, Département de biologie, Pavillon Vachon, Sainte-Foy, QC G1K 7P4, Canada.Université du Québec à Rimouski, Département de biologie et des sciences de la santé, 300, Allée des Ursulines, Rimouski QC G5L 3A1, Canada.
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The hypothesis of exploitation ecosystems (EEH) predicts that, along a productivity gradient in terrestrial environments, predators will regulate herbivores at a relatively constant density whenever primary productivity exceeds 700 g m−2 y−1; under this threshold, or if predators are absent, forage production determines herbivore density. I tested EEH using the pattern of deer biomass distribution over North America, the dominant family of large herbivores. Deer biomass increased from the High Arctic to the north of the boreal forest and remained in the same range southward within the gray wolf range; for the same latitude, deer biomass increased by a factor of 5 in the absence of wolves. South of the wolf range, there existed a clear relationship between actual evapotranspiration, a proxy of primary productivity, and deer biomass. Highest deer densities occurred in the south-east of the continent where only white-tailed deer are present. The observed pattern lends support to EEH and suggests that the removal of large predators in southern North America may have imposed an unprecedented pressure on plants eaten by deer.