Landscape - diversity relationships: ranking determinants of passerine species richness in the Vez watershed, Portugal

Climate change and landscape dynamics are among the most prominent worldwide drivers of biodiversity loss. They are causing changes in landscape patterns and processes, leading to impacts on biodiversity and ecosystem functions by changing the distribution of suitable environmental conditions for many species. The accelerated loss of biodiversity and of the ecological services it provides has led to an increasing concern and recognition of the profound consequences for human wellbeing, highlighting the urgent need of measuring environmental change efficiently. This study aimed to contribute to the improvement of conservation management by investigating the landscape ecological drivers of passerine diversity at the catchment level. A statistical modelling approach was developed and tested in the Vez watershed (NW Portugal), with the ultimate goal of establishing a framework capable of identifying groups of passerine species as indicators of the ecological state of the landscape. To assess the relation of landscape-level species richness with a set of environmental factors (climate, topography, habitat diversity, habitat disturbance, landscape composition, and landscape structure), we used a modelling framework consisting of five steps. Models based on environmental variables expressing each group of ecological factors were developed by Generalized Additive Modelling (GAM), and then ranked using a Multi-model Inference framework, according to the Akaike’s Information Criterion. We further assessed differences in model ranking for the whole species pool and for species groups based on habitat foraging and feeding traits. In order to control the potentially spurious sampling effort effect in models, we estimated the values for each response variable by fitting Species-Area Relationship (SAR), and then tested if this lead to an improvement of model performance. Overall, the framework developed originated models with good performances. Results showed that SAR-estimated values allowed improving model performance, compared to directly observed values, thus minimizing the effect of differences in sampling effort. However, despite this difference, the two sets of models were congruent regarding the ranking of landscape ecological determinants. Landscape structure and habitat diversity were found to be the main determinants of variation in passerine species richness at the local scale. We also found that different functional groups respond to distinct drivers according to their ecological requirements. The presence of insectivorous species was highly correlated with (and promoted by) habitat diversity, while open area specialist species richness was strongly determined by landscape structure. In turn, granivorous species stood out by being the only group whose richness distribution was ii FCUP Landscape – diversity relationships: ranking determinants of passerine species richness in the Vez watershed, Portugal mainly affected by habitat disturbance. Therefore, we suggest that these three groups may be used together as indicators of landscape ecological state in the Vez catchment. Our results provide a more profound insight of the landscape conditions driving local biological diversity, and encourage the implementation of management strategies that promote habitat diversity and landscape heterogeneity. In addition, this study improved the understanding of the response of passerine species to landscape structure, disturbance and habitat change, which can help target and prioritize conservation and management efforts while informing on the ecological status of landscape mosaics.