Facilitation studies have previously focused on the effects of plant–plant interactions on species richness and, more recently, on functional traits or phylogenetic aspects. Little is known, however, about the simultaneous effects that facilitation have on overall biodiversity, jointly considering taxonomic, functional and phylogenetic diversity. In this study, we investigated shrub facilitation on herb communities in a Mediterranean grassland over a 9‐year period (2007–2015), each year representing different water availability conditions. Taxonomic, functional and phylogenetic diversity indices were estimated using generalised Hill numbers within the integrated framework of attribute diversity. We used generalised linear mixed models to analyse the effect of shrub cover on the different diversity indices along a water availability gradient. Shrub cover had a positive effect on all attribute diversity indices, yet greater for abundant species. Shrubs also favoured survival of certain species (26.5% of total species), but above all they affected relative abundances of common species, filtering growth of dominant species (e.g., Poa bulbosa) and promoting evenness. Diversity indices accounting only for abundant (i.e., high coverage) species showed the strongest facilitation effects that peaked at mid‐range water availability conditions. Synthesis. Our results suggest that shrubs are key in the maintenance of all three dimensions of biodiversity in the Mediterranean grasslands, promoting more even communities, and to a lower extent, also species richness. We show that shrub facilitation on taxonomic, functional and phylogenetic diversity of herbaceous communities is maximum for abundant species at mid‐range values of water availability, in accordance with the humped‐back model. This study illustrates the need to evaluate different biodiversity dimensions from an integrated perspective, such as attribute diversity, to disentangle the role of facilitation in community assembly.
Accuracy of global bioclimatic databases is essential to understand biodiversity–environment relationships. Many studies have explored biases and uncertainties related to species distribution models (SDMs) but the effect of choosing a specific database among the different alternatives has not been previously assessed. The lack of bioclimatic congruence (degree of agreement) between different databases is a main concern in distribution modelling and it is critical in single‐source models, for which the database choice is decisive. In order to prevent unreliable predictions derived from distorted input data, SDMs accuracy can be assessed by mapping model predictions according to a bioclimatic congruence measure derived from the comparison of multiple databases, which can be achieved with the bioclimatic consistency maps that we propose in this study. Here, (a) we present the first global‐scale bioclimatic congruence map to analyse environmental mismatches between recently updated bioclimatic databases. We also test the importance of input matters on the reliability of distribution models of sixteen mammals, by addressing (b) inconsistencies among species response curves (temperature and precipitation), and (c) discrepancies among SDMs predictions depending on the chosen bioclimatic database. Finally, (d) we propose a strategy to assess bioclimatic consistency of model predictions, showing its application to the specific case of Litocranius walleri. Our results confirm that the single‐source modelling approach greatly influences the estimation of species–environment relationship and consequently, bias spatial predictions derived from SDMs. This is especially true for studies conducted in polar and mountainous regions which showed the smallest bioclimatic congruence. We show that by adding bioclimatic congruence to SDMs projections, we can build a bioclimatic consistency map that enables the detection of both risky and consistent areas, as revealed for the case of L. walleri. Assessing uncertainty in bioclimatic input data is key to avoid erroneous conclusions in macroecological and biogeographical studies. The spatial characterization of bioclimatic consistency provides an adequate empirical framework which effectively illustrates bioclimatic data limitations. We strongly recommend that this new strategy should be formally and systematically incorporated into distribution modelling to build more reliable SDMs, which are essential to develop successful biodiversity conservation programmes.
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