AUTHORS: V. Martín Izquierdo, PN Los Alerces, APN, Chubut, Argentina; Werner T. Flueck, CONICET, Argentina; JoAnne Smith-Flueck, Laboratorio de Teriogenología, “Dr. Héctor H. Morello” Facultad Ciencias Agrarias-Universidad Nacional del Comahue, Cinco Saltos, Río Negro, Argentina; Gabriel Bauer, PN Los Alerces, APN, Chubut, Argentina; Ricardo E. Gürtler, Laboratory of Eco-Epidemiology, Ciudad Universitaria, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina
ABSTRACT: The Patagonian huemul deer (Hippocamelus bisulcus) is the only South American cervid in danger of extinction. Only 1048-1500 individuals are remaining, fragmented into 101 subpopulations. 60% of those have only 10-20 deer1, compatible with pseudoextinction levels. The past range contraction of huemul follows a north-south and an east-west gradient related to certain anthropogenic activities2,3. The northern distribution has experienced the largest declines and fragmentation, with remaining huemul in high elevations of the Andes mountains1,2,4. Measures to reverse the effect of the supposed competition with livestock result in both success and failure generating discussions and little progress in understanding the cause-effect relationship. The present work characterizes observed patterns and proposes a hypothesis to explain them. One key observation is regarding the contradictions surrounding the biology of huemul. Studies on habitat selection based on remaining populations in northern Patagonia, even after the livestock removal, indicate a selection of high altitude areas which implicitly contradicts the knowledge about having lost traditional wintering areas as a cause of the contraction and population declines. Additionally, the causes of the population declines may be different to those resulting in failure of recovery. However, there is quantitative evidence that resident populations living at high elevations result in lower densities5. There are some cases where management strategies had been successful: Reserva Nacional Lago Cochrane6, Fiordo Témpanos7, Estancia Valle Chacabuco8 and the reintroduction in the National Park (NP) Torres del Paine9. These cases have resulted in quite rapid recoveries (λ=1,14-1,21), they are located in the best preserved area of the habitat gradient - in valleys and at low elevation; with high deer densities; absence or low levels of livestock, dogs and hunting; with dispersing animals and/or having relatively high reproductive rates. Similar management applied in other cases though did not result in recoveries: NP Los Alerces10 and PN Lago Puelo11. Other observations in NP Los Alerces5 or regarding habitat selection in Valle Esperanza12 could be merely consequences of failure in recovery. These cases differ from the previously mentioned examples in that resident huemul remain living at high elevations. We hypothesize that the loss of migratory behavior, at least altitudinal movements, is an ultimate factor which explains the failure to recover. Nutritional ecology13 is de frist hipótesis that use the loss of migratory behavior to explain failure in recovery. Secondarily, we propose that low deer densities reduce the success of the ‘rescue effect’14 and the recovery efforts. We understand that any hypothesis explaining such a dual response must generate hysteresis (loss of resilience). Huemul is strongly phylopatric and little or non-migratory15,16, probably artificially. In Odocoileus virginianus, phylogenetically related to huemul, the use of summer ranges is an acquired behavior, passed from the mother to the young during the first year17. They do not change their home range or migratory patterns, for instance, to colonize better habitat in neighboring areas, and show a high degree of site fidelity18. If the migratory behavior is acquired in huemul similarly as in other cervids, then the permanency of small and isolated groups in high mountain areas for several generations could provoke their local and independent loss of migratory behavior in metapopulations. This could explain why the successful and non-successful cases of recovery, the reported patterns of habitat selection and non-migratory behavior, and why the causes of declines and those that prevent recovery are different in the northern distribution where the species has suffered the major impacts. Although most parsimonious hypothesis does not require migration to explain the observed, we believe that including them is suitable for the habitat and the phylogeny of huemul.
