Bird species co-occurrence patterns in an Alpine environment supports the stress gradient hypothesis

Understanding the relative contribution of different biotic interactions in shaping species assemblages constitutes a major goal in community ecology and consequently, multiple methods aimed at inferring the nature of these associations have emerged during the last decade. In this framework, the stress-gradient hypothesis (SGH) predicts that prevalent biotic interactions shift from competition to facilitation as abiotic stress increases (and productivity decreases). This hypothesis originally raised by plant ecologists has been barely applied to faunal communities. Here, we take advantage of 20 years of abundance data to investigate pairwise patterns in species co-occurrence in Alpine bird communities inhabiting two contrasting habitat types; forests (high-productivity) and mountain grasslands (low-productivity). We also integrate functional data with presence-absence and quantitative matrices in order to detect the signature of processes driving community assembly and test for limiting...