Space use in desert areas by guanaco (Lama guanicoe) and its seasonal dependence on the most productive patches.

ACEVES PABLO; MALO, JUAN; SUAREZ FRANCISCO; BORGHI CARLOS; GIANNONI STELLA; TRABA, J.

The Netherlands

Congreso; 25 Years of Landscape Ecology: Scientific principles in practice. Proceedings of the 7 th IALE Worlds Congress. July 8 th -12 th. Wageningen,; 2007

Local habitat selection and seasonal movements are elements in life of many animal species as means to cover their vital needs. This is specially true far populations in areas close to species´s distribution extremes as theirproximity to the realizable niche limit makes survival more dependent on an efficient use of available resources. In this context, we describe seasonal variabiliti in space and habitat use by a small population of guanaco (Lama guanicoe Müller 1776) living at  he dryest limit of its Argentinean distribution. During the wet and dry seasons of 2005 and 2006 we GPS-located all guanaco observations obtained durinq sistematic surveys through the Ischigualasto Talampaya World Heritage Site (Argentina), located at the Phytogeographic region of the Monte Arido  dominated by shrubby plants such as Larrea spp, Zuccagnia punctata, Atriplex spp. and  Prosopis spp. in addition to several cacti species (Trichocereus, Cereus, Tephrocactus, Opuntia spp). Temperatures vary frorn minus 10º to 50°C and annual precipitation is about 100 mm.  Guanaco observatíons were obtained form dayly surveys of the area totailing approximately 150 hours by season. Variables of the environment and the group of animals were also colected for each observation.  We defined 6 different plant communities characterize the habitat where guanacos were found: dense scrubland (dominated by shrubs such as Zuccagnia punctata, Larrea cuneifofia and Geoffreadecorticans with >20% plant cover), open scrubland (with shrubs Iike Larrea spp and Plectocarpa tetracantha, always with <20% plant cover, and sometimes lower than 5%), treelike cacti-dominated slopes (hills covered by mixed shrubland with Trichocereusterschckii), algarrobal (Prosopis spp associated to dry rivers), zampal (sandy areas with a low cover of Atripiex spp), and peladal (barren areas). In all we carried out 209 observations of guanaco herds with a total number of 1343 individuals (mean ± standard error: 6.43 ± 0.29 animals by observation.  Mean group size varied significantly between years (ANOVA test F= 7.05; df=1, p=0.008), but not between seasons (ANOVA test F= 8.72; df=1, p=0.706).  The estimation of the all area ocupied by herds (Minimum Convex Polygons) showed a high seasonal overlap between wet and dry seasons (average for two years: Cole Concordance Index > 66%). Nevertheless, the analysis of the core areas (estimated using a density estimator kernel at 50%) showed a much lower seasonal overlap (average for two years; CCI <36%. Guanacos habitat selection was significantly different than expected from availability chi-squared= 71.41; df= 15; p<0.0001. Ivlev habitat selection index showed a somewhat relaxed selection pattern during wet seasons and a more neat one during seasons accordingly to this, guanacos showed preference for zampal and algarrobal during 2005 and 2006 wet seasons and avoidance of trelike cacti-dominated slopes and dense shrublands in 2005 and of zampal in 2006. However, in both dry seasons guanacos avoided peladal, and zampal in 2005 and algarrobal in 2006. No positive selection was recorded for dry seasons.   These fuzzy seasonal patterns were further analysed using a produclivity approach. We used satelite image (LANDSAT 7 ETM+) to analise guanacos habitat preferencess, from a regional approach, based on a Vegetation Index (NDVI) of the area.  NDVI for each guanaco location was calculated as the average in a 100 m buffer around it. NDVI estimated for dry season locations were significantly higher than for wet seasons (ANCOVA test F=35.09;  p<0.0001), apparently showing a preference towards the most productive patches of the area during dry seasons. The covariate number of guanacos per observation showed a tendency for larger herds to occupy locations of higher plant productivity.