Pablo Acebes

Niche segregation between wild and domestic herbivores in Chilean Patagonia.

Competition arises when two co-occuring species share a limiting resource. Potential for competition is higher when species have coexisted for a short time, as it is the case for herbivores and livestock introduced in natural systems. Sheep, introduced in the late 19th century in Patagonia, bear a great resemblance in size and diet to the guanaco, the main native herbivore in Patagonia. In such circumstances, it could be expected that the two species compete and one of them could be displaced. We investigated spatial overlap and habitat selection by coexisting sheep and guanaco in winter and in summer. Additionally, we studied habitat selection of the guanaco in a control situation free from sheep, both in summer and winter. We also determined overlap between species in areas with different intensity of use (named preferred and marginal areas) in order to further detect the potential level of competition in the case of overlapping. Guanaco and sheep showed significantly different habitat preferences through all seasons, in spite of their spatial overlap at landscape scale. Additionally, the habitat used by guanaco was similar regardless of the presence or absence of livestock, which further indicates that sheep is not displacing guanaco where they coexist. These results suggest that habitat segregation between guanaco and sheep is due to a differential habitat selection and not to a competitive displacement process. Therefore, the potential for competition is considered low, contrary to what has been previously observed, although this could be a density-dependent result.

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.

Abiotic gradients drive floristic composition and structure of plant communities in the Monte Desert

La definicion de comunidades discretas de plantas en zonas deserticas es complejo debido tanto a su homogeneidad a gran escala como a su heterogeneidad a pequena escala, lo que acaba generando dificultades para la toma de decisiones de conservacion. En este trabajo analizamos las comunidades de plantas del sector mas arido del Desierto del Monte en funcion de su estructura y composicion floristica. Se han utilizado tambien variables ambientales estimadas a pequena escala como la pendiente o la superficie de roca, suelo desnudo y hojarasca, asi como variables que operan a mayor escala como la diversidad de especies, la composicion floristica y la similitud dentro y entre localidades. Los analisis de composicion floristica resaltaron la dificultad para segregar diferentes comunidades debido al elevado nivel de heterogeneidad interna y de solapamiento floristico entre las distintas localidades estudiadas. Solo la comunidad situada en el extremo del gradiente de humedad edafica, el algarrobal, se segrego del resto. La ordenacion realizada sobre las variables estructurales en funcion del tipo de sustrato y de la cobertura arborea y de matorral segrego mejor las diferentes comunidades. Nuestros resultados muestran la dificultad para diferenciar comunidades de plantas en desiertos templados, sugiriendo la existencia de ensamblajes de especies relativamente estables en los extremos de los gradientes y de una gran heterogeneidad dentro y entre localidades. Las comunidades de plantas, por tanto, no pueden ser definidas unicamente por variables floristicas, sino que es preciso incluir informacion ambiental.

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.

Towards the identification and assessment of HNV Dehesas: a meso-scale approach

Iberian dehesa and montado are paradigmatic high nature value (HNV) agroforestry systems in Europe. Nevertheless their conservation status is uncertain as a consequence of their typological variety, different intensity of management practices on the ground, and other ongoing processes challenging their long-term sustainability. The existing broad gradients of dehesa and montado types impose difficulties in estimating not only their distribution and extent, but also their condition, since probably not all these agroforestry systems should readily be considered as HNV. Tackling with these difficulties, we explore a methodology based on GIS-analyses of land cover cartographies to estimate the extent and condition of dehesa farmland in an area covering ten municipalities in northern Andalusia region (Spain) based on: (1) integration of available thematic maps to obtain an improved land-use cartography; (2) application of GIS map generalization techniques to delimit potential HNV farmland types; (3) definition and calculation of several indices of ‘structural diversity’ and ‘impact’ within patches of dehesa farmland; (4) automatized weighted integration of indices to obtain a cartography assessing dehesa’s HNV in an ordinal scale from very low to very high. Estimated natural value was significantly worse for cultivated dehesas, with dehesas of pastures showing higher structural diversity and lower impact indices. Weaknesses and strengths of the proposed methodology are discussed.

Diffusive dispersal in a growing ungulate population: guanaco expansion beyond the limits of protected areas

Growth of wild ungulate populations within protected areas can cause an expansion towards surrounding non-protected areas and lead to conflicts with human activities. The spatial and demographic structure of colonizing populations inform about their state and potential trends, since the initial colonization by dispersing individuals precedes the establishment of a population with potential for further growth and expansion. Once colonization has succeeded, the spatial pattern of animal abundance is associated with intra- and interspecific interactions and environmental factors (e.g., habitat and food availability) and the population shows similar demographic features throughout the whole occupation area, which has been called a diffusive dispersal pattern. Here, we analyze the current status of colonization by a guanaco population of ranches surrounding a protected area in Chilean Patagonia with data gathered along three consecutive years. We thus compared animal abundance and social structure between the protected and unprotected areas and evaluated throughout the whole area the effect of environmental factors on guanaco abundance, proportion of family groups, and reproductive success. Guanaco abundance significantly declined with increasing distance from the center of the local distribution and marginally with predation risk. Moreover, social structure showed only minor differences between areas, pointing to a diffusive dispersal pattern. These results suggest that the population is already well established and has the potential to grow and continue its expansion. The case exemplifies a challenging outcome of successful animal conservation, and it presents a useful approach to evaluate the state of wild ungulate populations colonizing new areas.

Bridging gaps: On the performance of airborne LiDAR to model wood mouse-habitat structure relationships in pine forests

LiDAR technology has firmly contributed to strengthen the knowledge of habitat structure-wildlife relationships, though there is an evident bias towards flying vertebrates. To bridge this gap, we investigated and compared the performance of LiDAR and field data to model habitat preferences of wood mouse (Apodemus sylvaticus) in a Mediterranean high mountain pine forest (Pinus sylvestris). We recorded nine field and 13 LiDAR variables that were summarized by means of Principal Component Analyses (PCA). We then analyzed wood mouse’s habitat preferences using three different models based on: (i) field PCs predictors, (ii) LiDAR PCs predictors; and (iii) both set of predictors in a combined model, including a variance partitioning analysis. Elevation was also included as a predictor in the three models. Our results indicate that LiDAR derived variables were better predictors than field-based variables. The model combining both data sets slightly improved the predictive power of the model. Field derived variables indicated that wood mouse was positively influenced by the gradient of increasing shrub cover and negatively affected by elevation. Regarding LiDAR data, two LiDAR PCs, i.e. gradients in canopy openness and complexity in forest vertical structure positively influenced wood mouse, although elevation interacted negatively with the complexity in vertical structure, indicating wood mouse’s preferences for plots with lower elevations but with complex forest vertical structure. The combined model was similar to the LiDAR-based model and included the gradient of shrub cover measured in the field. Variance partitioning showed that LiDAR-based variables, together with elevation, were the most important predictors and that part of the variation explained by shrub cover was shared. LiDAR derived variables were good surrogates of environmental characteristics explaining habitat preferences by the wood mouse. Our LiDAR metrics represented structural features of the forest patch, such as the presence and cover of shrubs, as well as other characteristics likely including time since perturbation, food availability and predation risk. Our results suggest that LiDAR is a promising technology for further exploring habitat preferences by small mammal communities.

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.