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

The hypothesis of exploitation ecosystems (EEH) predicts that, along a prod uctivity gradient in terrestrial environments, predators will regulate herb ivores at a relatively constant density whenever primary productivity excee ds 700 g m(-2) y(-1); under this threshold, or if predators are absent, for age production determines herbivore density. I tested EEH using the pattern of deer biomass distribution over North America, the dominant family of la rge 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 r elationship between actual evapotranspiration, a proxy of primary productiv ity, and deer biomass. Highest deer densities occurred in the south-east of the continent where only white-tailed deer are present. The observed patte rn lends support to EEH and suggests that the removal of large predators in southern North America may have imposed an unprecedented pressure on plant s eaten by deer.