Functional response of fish communities in a multistressed freshwater world

• Published in: The Science of the total environment 2020-10, Vol.740, p.139902-139902, Article 139902
• Main Authors: Stefani, Fabrizio, Schiavon, Alfredo, Tirozzi, Pietro, Gomarasca, Stefano, Marziali, Laura
• Format: Article
• Language: English
• Subjects: Climate change; Exotic species; Fish; Functional diversity; Po plain; Redundancy
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.139902

Freshwater fish communities are impacted by multiple pressures, determining loss of functional diversity and redundancy. Our aim was to disentangle the roles and relevancies of different pressures in shaping fish communities in small streams of the Po plain (North Italy). Long term trend (1998–2018) of functional diversity of 31 fish communities was assessed and modeled in respect to three potential pressures: temperature increase, intensity of exotic fish invasion, and habitat quality degradation. Ecological traits mostly influenced by the pressures were also identified. Reduction of functional richness mostly due to local extinction or contraction of cold adapted predators, such as salmonids, was linked to increasing temperatures. Warming probably also led to a shift of generalist and dominant species, which became more abundant in streams hosting mixed communities of salmonids and cyprinids, and determined the increase of functional dispersion and uniqueness. Reduction of functional redundancy and increasing functional dispersion were both also related to the introduction of new ecological traits brought by expanding exotic species. Low functional overlap was found among native and exotic species, indicating that the invasion process was mainly controlled by competitive interactions and/or resource opportunism. Functional response to habitat quality was not clearly evident. In conclusion, the impact of temperature increase and exotic species on fish functional diversity was effective, idiosyncratic and mediated by the scale of analysis and by the intensity of pressures. [Display omitted] •Fish functional diversity in north Italy lowland streams changed in the last 20 years•Functional richness, dispersion and redundancy were affected by warming.•Top predators reduction and a shift of generalist fish was associated to warming.•Mild exotic fish invasion increased functional dispersion by introducing novel traits•Exotic fish decreased redundancy by competitive interactions or resource opportunism