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In this project, we thus aim at implementing this network approach by focusing on islets (i.e. islands lower than 3 km2), which can be considered sanctuaries of biodiversity as many species and interactions can only survive in them given that they tend to suffer less anthropogenic disturbances than larger islands. Such islets may indeed be considered potential reservoirs for future translocations and re-introductions of locally extinct species to larger, more species-poor neighbouring islands, functioning as effective safe havens for vulnerable interactions. By studying the food web structure (including both mutualistic and antagonistic interactions) in a total of six islets from six different archipelagos in three climatic zones (Balearics, Berlengas in the temperate zone;

Selvagens and Cape Verde in the subtropical zone; and Galápagos and Seychelles in the tropical zone), we aim at identifying the tipping point beyond which ecosystem functioning can collapse due to a disturbance, such as the loss of a keystone species due to the introduction of alien species. We will also evaluate the role of marine species (mostly seabirds) as connectors at the sea-land interface and how their nutrient transport to land influences the terrestrial food webs (regarding biomass, species richness and community composition of plants, and abundance, body size and dietary composition of animals). The reconstruction of the natural history of each islet community and the knowledge on its functioning will surely allow to foresee the fragility of the islets’ ecosystems to different types of disturbances and will thus be useful to environmental managers to elaborate better strategies for their conservation. A comparison between the diverse set of archipelagoes is only possible because each team member contributes complementary methodological tools and critical knowledge on a range of taxa at different locations. The set of skills provides us with a unique opportunity to address fundamental questions on the state of island biodiversity, its functioning and vulnerability to the effect of global change. The study of biotic interactions on islands is much biased towards a few emblematic archipelagos and, thus, this project will contribute to find general patterns in this aspect of island biology and to construct -hopefully in the near future- a global, generic model of island functioning and vulnerability.

Despite their much lower land extension compared to continental areas, islands harbor much of the world’s threatened biodiversity, mostly due to habitat degradation and loss, exploitation of natural resources and the introduction of alien invasive species. Understanding how island communities are assembled and function may help preventing the loss of such valuable biodiversity which consists not only of species but also of the interactions between them. With the advent of new theories and analytical tools, such as critical transition theory and complex network analysis, it is now possible to explore the architecture depicted as complex networks of interacting nodes as well as the functioning of communities.

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