Evaluating the potential causes of range limits of birds of the Colombian Andes

Aim To evaluate how factors acting at different spatial scales influence range limits in bird species of the Colombian Andes. Location Andes Mountains of Colombia. Methods We used Maxent , a climate envelope model (CEM), and environmental and geographic information to study range‐filling (i.e. the extent to which a species occurs in all the areas in which it is predicted to occur) in 70 range‐restricted bird species of the Colombian Andes. Environmental data were taken from the WorldClim database, and species occurrence data were taken from museum data collated by the BioMap project, an observational database, and the literature. We evaluated how climate and geographic barriers may shape range limits at two scales. Results At a broad extent (i.e. across the three main cordilleras within the Colombian Andes), we find that CEMs predict there to be suitable environmental conditions for particular species in regions where the species is absent, possibly as a result of dispersal limitation or biotic interactions. In contrast, at a finer scale (within a given cordillera), species generally occur across the entire area predicted to be suitable by a given CEM. Geographic discontinuities within cordilleras do not generally correspond to range limits; instead, range limits correspond to changes in environmental conditions. Main conclusions Our results suggest that different mechanisms influence the presence of species at different scales. Dispersal limitation, potentially combined with species interactions, may influence range limits at a broad extent (the entire Colombian Andes), while strong environmental gradients correspond to range limits at a finer scale (within a cordillera).