Ramiro Ovejero

Density and habitat use at different spatial scales of a guanaco population (Lama guanicoe) in the Monte desert of Argentina

Abstract The first density estimates of a peripheral guanaco population and its habitat use at different spatial scales are presented for a protected area of Monte desert, Argentina. Transects were surveyed in the wet and dry seasons of 2005. All guanaco herds observed during systematic surveys using roads and tracks were GPS located and their habitat use was identified. Herd size differed significantly between the dry and wet seasons. Population densities differed between wet (0.10–0.12 individuals/km2) and dry seasons (0.60–0.75 individuals/km2). The population estimates ranged from 75 individuals (dry season) to 388 individuals (wet season). Guanacos showed differential habitat use, the first determinant being abiotic factors, such as topography, soil characteristics or microclimate conditions, animals being detected in rougher rocky substrata in the dry season and in open flat terrain in the wet season, followed by a mesoscale selection defined by plant communities. At the latter scale, guanaco preferentially used mixed creosote bushland and saltbush more intensively during the wet season, and open scrub and columnar-cactus slopes in the dry season. The estimated population of this protected area was small but its population density was within the range of other populations and was relatively high for this dry and unproductive area.

Lack of feral livestock interference with native guanaco during the dry season in a South American desert

Analyzing coexistence of exotic and native ungulates in arid areas is important from both a theoretical and a species conservation perspective. We assess the habitat use patterns and possible interference between guanaco (Lama guanicoe) and feral livestock (donkey and cattle) in arid environments of South America. To determine habitat use and niche overlap between exotic and native ungulate species, ten sites with different habitats and six natural waterholes were selected. Plots (20 at each site, ten around each waterhole) were randomly set up and characterized by environmental variables and relative use by cattle, donkey and guanaco through faecal pellet counts. Aggregation, niche breadth and niche overlap of the three herbivores were analyzed at habitat level (mesoscale). A direct redundancy analysis was used to examine the relationships between abundance of herbivore faeces and environmental variables at microscale. Mesoscale analyses showed (i) an extensive use of the area by all three species, with guanaco having the highest niche breadth followed by donkey and cattle and (ii) a large, broad guanaco–donkey and donkey–cattle habitat overlap. However, results at a finer scale showed high spatial aggregation of feral livestock species and an independent use of territory by guanacos. This study is the first to provide information about habitat partitioning between guanacos and feral livestock in the hyper-arid Monte Desert biome and points to an apparent lack of negative effects on the native ungulate.

Spatial and seasonal dynamic of abundance and distribution of guanaco and livestock: insights from using density surface and null models.

Monitoring species abundance and distribution is a prerequisite when assessing species status and population viability, a difficult task to achieve for large herbivores at ecologically meaningful scales. Co-occurrence patterns can be used to infer mechanisms of community organization (such as biotic interactions), although it has been traditionally applied to binary presence/absence data. Here, we combine density surface and null models of abundance data as a novel approach to analyze the spatial and seasonal dynamics of abundance and distribution of guanacos (Lama guanicoe) and domestic herbivores in northern Patagonia, in order to visually and analytically compare the dispersion and co-occurrence pattern of ungulates. We found a marked seasonal pattern in abundance and spatial distribution of L. guanicoe. The guanaco population reached its maximum annual size and spatial dispersion in spring-summer, decreasing up to 6.5 times in size and occupying few sites of the study area in fall-winter. These results are evidence of the seasonal migration process of guanaco populations, an increasingly rare event for terrestrial mammals worldwide. The maximum number of guanacos estimated for spring (25951) is higher than the total population size (10000) 20 years ago, probably due to both counting methodology and population growth. Livestock were mostly distributed near human settlements, as expected by the sedentary management practiced by local people. Herbivore distribution was non-random; i.e., guanaco and livestock abundances co-varied negatively in all seasons, more than expected by chance. Segregation degree of guanaco and small-livestock (goats and sheep) was comparatively stronger than that of guanaco and large-livestock, suggesting a competition mechanism between ecologically similar herbivores, although various environmental factors could also contribute to habitat segregation. The new and compelling combination of methods used here is highly useful for researchers who conduct counts of animals to simultaneously estimate population sizes, distributions, assess temporal trends and characterize multi-species spatial interactions.

Different factors that modify anti-predator behaviour in guanacos ( Lama guanicoe )

Animals optimize the trade-off between the cost of not fleeing and the benefits of staying because the factors that influence flight decisions and the disturbance level of a particular stimulus can vary both spatially and temporally. Different factors (human impact and habitat characteristics) likely to modify anti-predator behaviour in different types of guanaco social groups were analysed. We found that group size was conditioned by high poaching, vehicle traffic, predation risk and vegetation density. Solitary adult males showed shorter alert and flight initiation distances than bachelor and mixed groups. Alert distance was greater during the summer season, and assessment times were shorter when young were present in the groups. In high-predation-risk environments, guanacos detected threats at greater distances and flight initiation distance was longer. Alert distances were shorter on steeper sloped hills and assessment times were shorter in areas with irregular topography than on flat sites. In high traffic areas, flight initiation distance was longer and assessment times were shorter. And in areas with low poaching intensity, assessment times were greater than in those with high poaching levels. Therefore, guanacos may be able to evaluate a true threat. Social group and anti-predator responses were conditioned by habitat characteristics and human impact. We consider that plasticity of responses could be key to the survival of guanacos.

Vigilance behaviour of the year-round territorial vicuña (Vicugna vicugna) outside the breeding season: Influence of group size, social factors and distance to a water source

We conducted focal observations of vicuña, a year-around territorial mammal, to compare vigilance behaviour between territorial and bachelor males outside the reproductive season. We hypothesized that the time spent vigilant would depend on male social status, considering the potential effects of several variables: sampling year, group size, distances to the nearest neighbour and to a vega (mountain wetland). We fit GLM models to assess how these variables, and their interactions, affected time allocation of territorial and bachelor males. We found non significant differences between territorial and bachelor males in the time devoted to vigilance behaviour. Vigilance of territorial males was influenced by the sampling year and the distance to the vega. In turn, vigilance in bachelor males was influenced mainly by the sampling year, the group size and the distance to the vega. Our results suggest that sampling year and distance to the vega are more important than social factors in conditioning the behaviour of male vicuñas, during the non-reproductive season. Future studies of behaviour in water-dependant ungulates, should consider the influence of water and forage availabilities, and the interactions between group size and other variables.

Habitat selection and coexistence in small mammals of the southern Andean foothills (Argentina)

Habitat partitioning is considered one of the main mechanisms of coexistence among small mammals. This is especially evident in arid environments where resources are particularly scarce. Habitat characteristics such as vegetation heterogeneity and complexity are expected to increase species coexistence, increasing the number of microhabitats that can be occupied by species with different requirements. The Andean foothills can be considered as an ecotone between the Monte and Altoandina phytogeographic provinces as they harbor species from both. Consequently more species are thought to coexist in this area. The objectives of this study were to assess the macro- and microhabitat selection of the small mammal assemblage inhabiting the Andean foothills during wet and dry season and to determine how animals segregate environmental resources to ensure their coexistence. We found that habitat selection occurs at both scales in the Andean foothills. Two species, Eligmodontia moreni and Phyllotis xanthophygus, were capable of distinguishing among macrohabitat types, whereas all species showed habitat selection at the microhabitat scale. We registered selection during both seasons, with some overlap of resource selection during the wet season and the greatest segregation of microhabitat resources during the dry season. Therefore, this work evidence that the assembly of small mammals is sensitive to habitat structure especially in dry seasons where resources are constraints due to arid conditions of Andean foothills.

Effects of live-shearing on population parameters and movement in sedentary and migratory populations of guanacos Lama guanicoe

Live-shearing of wild guanacos Lama guanicoe may affect their reproductive success and population resilience, and therefore it is important to assess the biological sustainability of obtaining their wool. We evaluated effects of capture and shearing on survival and reproduction, population parameters, daily movements, ranging behaviour and spatial distribution in sedentary and migratory populations. We assessed population variables by radio-telemetry and line-transect surveys before and after capture. We estimated high post-shearing survival rates in both populations and similar yearling production in shorn and non-shorn females in the migratory population. We did not find significant variations in density and population structure before and after shearing in the sedentary population, whereas in the migratory population density decreased and the population structure changed significantly after assembly of the capture structure, returning to pre-assembly levels 1 month later. The mean daily distance moved by radio-collared guanacos during the first 2 days after shearing was three times longer than during the following 30 days. There was a 25% decrease in the mean home-range size of shorn guanacos between the first and second month after shearing but this decline appeared to be associated with a seasonal change in movement, because a similar reduction occurred during the same period the following year, when the guanacos were not shorn. Live-shearing modified the spatial distribution pattern in the sedentary population but did not have a significant effect on the migratory population. Management of guanacos may contribute towards developing a biologically sustainable economic activity that promotes conservation of wildlife and habitats.

Different responses of free-ranging wild guanacos (Lama guanicoe) to shearing operations: implications for better management practices in wildlife exploitation

Fil: Taraborelli, Paula Andrea. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Aridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Aridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Aridas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina

Sympatric guanacos and livestock share water resources in drylands of Argentina

Abstract There is growing concern about the effect of livestock on wild ungulate populations, particularly in arid ecosystems, where waterholes are an extremely scarce resource, around which animals tend to gather, primarily in the dry season. This situation is worrying in South American deserts, where guanaco is the native species that often shares trophic and water resources with livestock from local communities, even inside protected areas. We assess through general linear modeling (GLM) the use of waterholes by guanaco and two introduced species, free-ranging cattle and feral donkeys, during the summer-wet and winter-dry seasons, in an arid, water-limited region in northwestern Argentina. Waterholes were more intensively used in the dry than the wet season by all three herbivores. However, introduced ungulates did not use all of the waterholes, whereas guanaco used them all with equal intensity, which points to an apparent absence of interference probably due to the low density of the introduced species. Nevertheless these results could mask negative effects regarding the risk of parasite transmission, the under-use of one of the waterholes, and the risk related to increasing livestock density in a near future. Therefore, it would be advisable to make long-term monitoring to prevent potentially negative effects on guanacos.