Species occurrence depends on both environmental and biotic factors (species interactions). Consideration of species interactions when estimating functions of population distribution is unusual, and may be crucial to understand and predict how species use space and resources. In this study, we combine resource selection probability functions (RSPFs) with a model selection approach based on information theory to evaluate how biotic (interspecific interactions) and abiotic (environmental) factors affect resource selection of guanacos Lama guanicoe and livestock (goats, sheep, cattle and horses) in two seasonal periods. We first test different a priori hypotheses of the environmental effects on guanacos and livestock occurrence (i.e. foraging, predation/topography and human effect hypotheses), then we assess model performance with independent data, and finally we use validated models of each species as predictors of the interaction between them. In all seasons, L. guanicoe occurrence was influenced by both environment and livestock interactions, especially small livestock (goats and sheep). Guanacos selected for habitats characterized by high temporal variability in plant productivity and away from potential human contact. In all seasons, L. guanicoe was negatively related to the RSPF of small livestock, but the reverse was not the case, suggesting that L. guanicoe avoids sites used by goats and sheep. In contrast, livestock was mainly affected by environmental variables related to human presence and was not affected by the interactions with herbivores. Contrary to our predictions, goats and sheep were also associated with less productive sites, probably indicating strong degradation of the sites to which they are restricted. Our results suggest a spatial segregation between L. guanicoe and domestic herbivores throughout the year, which is explained by competitive interactions of L. guanicoe with small livestock but also in response to vegetation productivity and human pressure. This study shows the importance of including species interaction effects in habitat modeling.
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