Programma della conferenza

The ongoing and predicted loss of biodiversity due to anthropogenic stressors, including climate change, pose significant threats to ecosystem functioning, and ultimately to ecosystem services upon which humans depend. The potential ecosystem functions in natural systems are given by the biological diversity within it, since the functional traits and main ecological attributes of the species within it are responsible for most of the ecosystem processes. Particularly in marine environments, these impacts can be profound, altering from small scale biogeochemical cycles to the overall resilience of an ecosystem. This research will contribute to the understanding of the intricate relationships between biodiversity and ecosystem functioning, by studying the mechanisms linking biodiversity change/loss in marine environment multifunctionality. We employ the novel Aquatic Eddy Covariance (AEC) technique (Berg et al., 2003) to measure vertical turbulent fluxes of oxygen that are widely used proxy for benthic mineralization and primary production, and from which we can derive daily metabolic rates of respiration (R), gross primary production (GPP), and net ecosystem metabolism (NEM). AEC provides a in situ non-invasive approach, minimizing ecosystem disturbance while integrating the flux over a large benthic surface area with strong spatial heterogeneity. In this context, AEC can be used to measure ecosystem functioning related to primary production and carbon sequestration. These functions measured together with other such as those for nutrient cycling, can then be studied in relationship with the associated biodiversity (ideally across different trophic levels and in varying temporal and/or spatial scales). The relationships found between these two components of ecosystems, could provide a good picture of how the biodiversity present is contributing and shaping the functions independently, or together simultaneously (multifunctionality). Preliminary results are presented from a case study on Mediterranean seagrasses and mixed macroalgae communities in the Stagnone di Marsala coastal lagoon, in Western Sicily.

Climate warming is expected to affect nutrient transfer in food webs, with pronounced effects in the Arctic due to warming amplification and nutrient-limited conditions. Arctic lake ecosystems represent biodiversity hotspots and carbon sinks of global value. Declining snow coverage is increasing primary productivity and herbivore abundance in lake catchment areas, which represent key drivers of nutrient input. However, predicting climate change effects on Arctic lake food webs remains challenging, hindering the conservation of these fragile ecosystems and their services.

This study examines the effect of snow coverage and consequent migratory bird density (Branta leucopsis) on lake food webs. We analyzed nine shallow lakes along a gradient from the coastline to glaciers on the Brøgger Peninsula, Svalbard. Using gas-flow measurements and C and N isotopic analysis, we assessed nutrient sources, CO₂ emissions, and trophic interactions. Bayesian mixing models were employed to investigate the diet of Lepidurus arcticus, a key omnivorous species in lake food webs.

Decreased snow coverage led to an increase in primary productivity and geese abundance around lakes. In turn, organic inputs from geese increased N concentration in sediments and improved the stoichiometric quality of aquatic vegetation. This led to two primary effects: (i) a fourfold increase in CO₂ emissions from sediments, and (ii) a dietary shift in L. arcticus towards greater consumption of sediments, which store long-term C, and aquatic vegetation, containing newly fixed C, thereby reducing its intake of animal prey. These changes resulted in a 12-17 gC m^-2 year^-1 increase in C flow from basal resources to upper trophic levels, reducing potential long-term C accumulation.

By linking CO₂ emissions and C transfer in food webs to variations in snow coverage, vegetation, and geese abundance, this study advances our mechanistic understanding of the cascading effects of climate change on Tundra ecosystems and their capacity as carbon sinks.

Herbivory shapes the structure and functioning of forest ecosystems worldwide. However, little is known about its potential environmental drivers such as water availability and multi-scale effects of herbivore population density in Mediterranean forests, where water availability is becoming scarcer and further predicted to drop over the next decades.
During 4 years (2019-2023), we investigated the factors affecting browsing pressure by wild deer (roe deer Capreolus capreolus and fallow deer Dama dama) on the woody vegetation belonging to the Natura 2000 EU Habitat 9340 ‘Quercus ilex and Q. rotundifolia forests’, within a Mediterranean protected area (central Italy).
Browsing impact increased with increasing fallow deer densities at multiple scales, but was not affected by roe deer densities. This occurred at the whole habitat patch scale and separately for both the most dominant typical species/genera of Habitat 9340 in our study area (Quercus ilex; Phillyrea spp.). Greater population density, larger body size, more generalist diet, and higher gregariousness likely underpin the major impact of fallow deer. During our study, the ~25% decline in fallow deer density matched the increased numbers of wolves, whose diet included fallow deer (~25%). This result may support consumptive effects of predation leading to the top-down control of deer impact on vegetation.
Herbaceous cover in forest patches diluted browsing pressure, indicating how the availability of alternative resources may mitigate deer impacts on woody vegetation. Contrary to expectations, higher rainfall increased browsing, suggesting resprouting of woody plants with enhanced palatability/nutrient content, increasing attractiveness to deer. This finding implies that browsing impact on Mediterranean forests would occur even when water availability increases, if herbivore density remains high.
Our work emphasises the critical roles of spatiotemporal variations in population densities of wild herbivores in driving their browsing impact on natural habitats, offering valuable insights into the conservation of Mediterranean forests.