Anthropogenic Pressure and Climate Change Could Severely Hamper the Avian Metacommunity of the Sicilian Wetlands

Our study shows that the current levels of anthropogenic exploitation of the Sicilian wetlands (Italy), combined with the likely exacerbation of climate-driven variables, are unsustainable and could soon exclude many bird species from this metacommunity. Sicily is the largest island in the Mediterranean Sea, and its wetlands represent a network of unreplaceable stopover sites that allow waterbirds to rest and refuel during migratory journeys along the central-eastern Mediterranean bird flyway. During the summer period, these species experience higher levels of environmental stress as water scarcity and anthropogenic pressure are at their peak. Through field surveys, geoprocessing and statistical analyses, we investigated: (a) the structure of the avian metacommunity of the largest Sicilian wetlands during July-September and (b) the effects of 10 (geographic, hydrological and anthropogenic) wetland attributes on avian diversity. We sampled 73 bird species, of which 30 are listed in annex I of the Birds Directive. The avian metacommunity was significantly nested and non-modular; in addition, it presented elevated beta diversity and random species assemblage. Environmental filtering superseded biotic interactions in determining species composition. Avian diversity was significantly favored by higher water levels, water-level fluctuations and water discharges, and disfavored by water diversion, salinity and tourism pressure. The knowledge concerning the particular structure of the avian metacommunity of the Sicilian wetlands can facilitate the implementation of conservation policies that could mitigate and compensate the effects of short- and mid-term risks.