| Summary: | Recent policies on the ban of fishing discards and the closure of open-air landfills are expected to reduce amount of predictable anthropogenic food subsidies (PAFS) for seabirds. To forecast the ecological consequences of these policies, it is necessary to understand the influence that each of these resources has on ecological parameters and how this can be mediated by density-dependent mechanisms. Besides, for those species exploiting both types of resources, it is important to consider whether or not their effects act synergistically. Finally, it is also important to understand how the ecological interactions between seabirds and PAFS can be influenced by other potentially important environmental factors, such as for example, the abundance of natural prey or the one of foraging conditions. In the first chapter of this thesis, I reviewed the current knowledge on the ecological interactions between seabirds and fishery discards, with the aim of identifying the main knowledge gaps and to propose new challenges to improve our understanding of the ecological role of PAFS availability to seabirds. In the second chapter, I assessed the relative role of fishery discards and open-air landfills in the breeding investment of a generalist seabird, investigating the possible interplay with density-dependent mechanisms. In the third chapter I collaborated to investigate the role of PAFS in buffering environmental stochasticity and disrupting the natural synchronous dynamics between two seabirds. Finally, in the last chapter, I assessed the importance of several environmental factors in the breeding investment of three seabirds with contrasting life-history strategies. In particular, I considered local environmental variables (food abundance, competition and sea state) during breeding as well as the influence of winter conditions summarized by a large-scale climatic index, the North Atlantic Oscillation (NAO). Considering these variables simultaneously allowed me to assess the relative importance of natural and ...
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