Exotic deer in southern Latin America: what do we know about impacts on native deer and on ecosystems?

Abstract

A recent review on exotic cervids concluded that deer introduced to Patagonia impacted habitat and native huemul deer Hippocamelus bisulcus. I evaluate these assertions and amend information about this South American case study. Categorizing deer along narrow characteristics may be too restrictive to allow accurate predictions about interactions. More effective is considering the magnitude of plasticity (behavioral, phenotypic, genetic). The dichotomy of native versus exotic deer masks situations where prevailing ecological conditions are far from ‘native’, such as absence of predators, and such results from artificial settings have limitations. Studies used to contrast effects on vegetation from exotic red deer (Cervus elaphus) versus native huemul did not analyze native deer and provided no data to support conclusions in the review. Huemul were concluded to have high trophic overlap with red deer whose diet, however, was determined in another habitat where the food item of supposed major overlap was absent, and suggesting that red deer might cause exploitation competition was not supported by cited data. There was no mention that huemul are foremost exposed to livestock rather than exotic deer. Concluding that exotic prey including red deer increase predator density resulting in increased predation of huemul (apparent competition), was not supported by cited studies. To the contrary, high-density puma (Puma concolor) could not prevent guanaco (Lama guanicoe) from increasing >13-fold, nor that huemul expanded into these sites. Not only were those studies opposite to conclusions in the review, but none had studied huemul nor predator population trends. Data from little known species like huemul should be used with reservations when aiming at generalizations.