SPATIAL STRUCTURE OF POPULATIONS OF GUANACOS, LESSER RHEAS AND MARAS IN AN ARID SOCIO-ECOSYSTEM. THE INFLUENCE OF HABITAT AND SHEEP RANCHING IN PENÍNSULA VALDÉS

ANTUN MA DE LOS MILAGROS

Mastozoología Neotropical

Mastozología Neotropical

Lugar: Buenos Aires; Año: 2018 vol. 25

1666-0536

The spatial structure of wild-herbivore populations ? guanacos, lesser rheas and maras ? was studied in Península Valdés (PV), Chubut Province. Models accounting for the variation in the abundance of the studied species were used to assess the natural and anthropogenic factors involved, and to analyze the co-occurrence and segregation patterns between the wild herbivores and the domestic sheep in the study area.Guanacos, lesser rheas and maras make up the assemblage of large native herbivores widely distributed across the arid Patagonia. The spatial structure of their populations responds both to species-specific factors, habitat characteristics and the ecological processes affecting their distribution and abundance. The domestic sheep was introduced in Patagonia by the end of the 19th century. Within a few decades, millions of sheep were grazing on the native vegetation, resulting in a major disturbance for the habitat and for the populations of wild herbivores. The geographic and ecological characteristics of PV, its importance for conservation ? it is a Natural World Heritage Site (UNESCO) with managed resources (category VI IUCN) - and for the regional economy, are all relevant factors at the time to analyze the spatial structure of wild herbivores populations within a matrix of livestock production. Ground line transect surveys were carried out along more than one thousand km of roads and secondary tracks in PV, between March and May of 2015, 2016 and 2017. After both natural and anthropogenic variables were obtained and defined for the study area, Density Surface Models (MSD) and Null Models (MN) were constructed to evaluate the spatial structure of each species.Results of abundance of guanacos, maras, lesser rheas and sheep were obtained for PV at a resolution of 4 km2. Intermediate and high NDVI values (between 0,07 and 0,2) - a correlate of primary productivity - were associated with a decrease in the abundances of guanacos and lesser rheas. Between the anthropic variables, the proximity to ranch buildings had a strong negative effect on guanacos, although positive in the abundance of maras, while the proximity to the nearest fence implied a negative effect on the abundance of lesser rheas. Guanacos showed spatial segregation with sheep, while maras showed a pattern of aggregation with lesser rheas.This thesis contributes to the knowledge of the mechanisms and variables that model the spatial structure of the assemblage of native herbivores in the arid Patagonia, within a site of a high relevance for conservation and for the regional economy that depends on the livestock activity and also on the tourism attracted by biological diversity. Also, this work integrates methodological tools that allow a thorough analysis of the spatial variation in the abundance of the selected species. The results obtained through the application of MSD and MN suggest that it is important to incorporate these tools to extend the research to other areas in the region, and to monitor responses to management and conservation actions of wild populations.