Recent advances in the nutritional ecology of the Patagonian huemul: implications for recovery

Abstract

Huemul (Hippocamelus bisulcus) numbers had already declined drastically by the 1800s. Only ~500 animals remain along 1800 km of the Argentine Andes between 34 and 54°S, without cases of recolonisation or numerical responses. In Chile, at least two populations have increased; the remaining populations have either decreased or are assumed to be stable. During a Chilean–Argentine meeting in 1992 several factors were hypothesised to be important for huemul recovery (cattle, exotic trees, irrational forestry, exotic animals, illegal hunting, diseases, dogs, reduced numbers), but these can be rejected as key explanations for the general lack of recovery. Each factor may play an additive role – alone or in combination – in certain populations, but none of them are likely a primary cause. Our objective is to evaluate alternative factors and several indications warrant us to postulate that nutritional ecology instead plays a central role in the general absence of recovery. A wide range of antler quality is encountered among huemul today, with well developed specimens known primarily from historic times. If antler expression in huemul is homologous to other cervids, it follows that most extant populations are under suboptimal conditions. Another important clue is a high prevalence of age-independent osteopathy among adults. We hypothesised that such generalised secondary chronic alveolar osteomyelitis, osteoarthritis and periodontitis were hypothesised to relate to nutritional ecology. Meagre antler development with frequent asymmetry, high prevalence of osteopathy, and low recruitment rates could all be related to common and limiting nutritional factors known to cause the described phenomena. Initial investigations point to several lines of evidence that support the hypothesis that deficiency in iodine and selenium (Se) might be involved. Among other things, such deficiencies impair bone growth, reproduction, neonatal development, the immune and nervous systems, and cause periodontitis in ruminants. Se deficiency directly affects iodine metabolism. Only decades ago, overt iodine deficiency in humans living in these areas was very common. For free-ranging livestock, overt Se deficiency has been described in Chile: supported by geology, pedology, topography, and climatic patterns. It is well known that valley bottoms, flood plains, and habitats downwind from glacial areas provide higher provision of iodine and Se. The nexus to the nutritional ecology of huemul likely is the inaccessibility of most traditional winter ranges, elimination of migratory traditions, and concomitant elimination of source populations. Se and iodine provisions diminish with altitude, which at the same time increases physiological needs due to hypoxia, and intensified radiations and exercise. Most extant huemul populations occur in remote high-altitude refuges, or inaccessible Pacific coastal areas. Migration, an acquired behaviour, has been eliminated through past overhunting of this population segment; huemul being very vulnerable to human predation were killed by the thousands to feed people, dogs, chicken and pigs, and their skins were used for shelters. Huemul currently dispersing from refuges are generally being killed when entering former source areas now occupied by settlers and their dogs. Other ungulates driven into mountain refuges have been shown to be deficient in these trace minerals and responded well to mitigation of the deficiency. Thus, prevention of reaching traditional winter ranges or valley bottoms might result in inadequate mineral supply to huemul.