Dottorato in BIOLOGIA AMBIENTALE ED EVOLUZIONISTICA

Titolo della tesi: Variation in the structure of food webs related to climate change and anthropogenic disturbance

Climate change and anthropogenic pressure are deeply altering the global environments dramatically threating the persistence of biodiversity and ecosystems processes including the primary production, matter cycling and energy flux. However, the still scarce knowledge on the biodiversity organization in the food web structure, and not only on the species number, limits our power to predict the effects of environmental change and the possible response mechanism of biological community to environmental variations. This work aims to understand the mechanism underlying the community structure and its stability under different natural or anthropogenic pressures conditions. The food web structure and its metrics, the main carbon pathways and the taxa that play a key role in the community organisation in aquatic ecosystems were identified and quantified. The extensive field sampling and stable isotope analysis of each individual collected in the study ecosystems allowed to reconstruct and compare highly detailed food webs and trophic niche at both spatio-temporal and hierarchical scale (from individuals to community). In addition, the new consideration of trophic specie based on restricted interval of two elements isotopic signals, proved to be an efficient approach to overcome the current limits of the classical food web reconstruction, that occur when the biodiversity and the possible trophic interactions between species within an ecosystem are particularly complex. Our results highlight that modifications in the availability and quality of basal resources alters the interactions among organisms at different hierarchal scale with cascade effects on the entire food web structure, complexity, and stability. In accordance with optimal foraging theory, the availability of food sources has imposed change of link density already starting from single individuals with important variation of recurring patterns in the food web structure. Specifically, the consumers diet breadth decreased when the per capita availability and quality of resources increase. This, in turn, led to a relatively simpler food web characterized by lower link density affects the stability of the community against biodiversity loss and biological invasions. Our results are of particular relevance for ecology and for methodology, providing the key information for understanding the mechanisms that structure the community and its possible response to the different disturbance conditions. The results support that the expected changes in the habitat physical conditions could be reflected in food web architecture and organisms with greater generalism and trophic plasticity may be able to persist after a disturb playing a key role in community stability. The structure and function of food webs could be an efficient measure to predict and mitigate the effect of induced both physical and biological change on natural communities, both in the short and medium-long term (including climate change).