Aims The 50th anniversary of the publication of the seminal book, The Theory of Island Biogeography, by Robert H. MacArthur and Edward O. Wilson, is a timely moment to review and identify key research foci that could advance island biology. Here, we take a collaborative horizon‐scanning approach to identify 50 fundamental questions for the continued development of the field. Location Worldwide. Methods We adapted a well‐established methodology of horizon scanning to identify priority research questions in island biology, and initiated it during the Island Biology 2016 conference held in the Azores. A multidisciplinary working group prepared an initial pool of 187 questions. A series of online surveys was then used to refine a list of the 50 top priority questions. The final shortlist was restricted to questions with a broad conceptual scope, and which should be answerable through achievable research approaches. Results Questions were structured around four broad and partially overlapping island topics, including: (Macro)Ecology and Biogeography, (Macro)Evolution, Community Ecology, and Conservation and Management. These topics were then subdivided according to the following subject areas: global diversity patterns (five questions in total); island ontogeny and past climate change (4); island rules and syndromes (3); island biogeography theory (4); immigration–speciation–extinction dynamics (5); speciation and diversification (4); dispersal and colonization (3); community assembly (6); biotic interactions (2); global change (5); conservation and management policies (5); and invasive alien species (4). Main conclusions Collectively, this cross‐disciplinary set of topics covering the 50 fundamental questions has the potential to stimulate and guide future research in island biology. By covering fields ranging from biogeography, community ecology and evolution to global change, this horizon scan may help to foster the formation of interdisciplinary research networks, enhancing joint efforts to better understand the past, present and future of island biotas.

Aim Four long‐distance dispersal (LDD) modes have generally been considered to play central roles in the colonization of islands by plants: anemochory (dispersal by wind), thalassochory (dispersal by oceanic currents), endozoochory (internal dispersal by animals) and epizoochory (external dispersal by animals). However, seeds can also be transported by vectors different from those to which they are best suited (non‐standard dispersal), meaning that the actual vector of colonization cannot be inferred based on diaspore traits alone. We propose an alternative approach to explore the relative contribution of LDD syndromes to island colonization. Location Europe and the Azores. Methods We scored the presence of syndromes relevant for LDD in the native flora of Europe (c. 10,000 species) and the Azores (148 species). We then contrasted the importance of each syndrome in the recipient flora (Azores) and the source floras (Europe and mainland Portugal) to estimate which, if any, syndrome was particularly successful for overseas colonization. We further investigated whether particular LDD syndromes increased plant distribution within the Azores archipelago. Results Most native species in Europe (63%), mainland Portugal (67%) and the Azores (63%) produce unspecialized diaspores. Only species adapted to sea dispersal were overrepresented in the Azores, while those adapted to wind dispersal were underrepresented. The presence of LDD syndromes did not significantly improve the distribution of plant species across the archipelago, except for the moderate advantage of endozoochorous diaspores. Differences in the importance of LDD syndromes across plant families at least partially explain the floristic disharmony of the Azorean flora. Main conclusions Only thalassochory appeared to have significantly favoured the colonization of the Azores. The high proportion of unspecialized diaspores, the unexceptional representation of most specialized LDD syndromes and the dissociation between syndromes and inter‐island plant distribution in the Azores suggest that non‐standard events are more common than previously believed in the colonization of islands by plants.

The unique biodiversity of most oceanic archipelagos is currently threatened by the introduction of alien species that can displace native biota, disrupt native ecological interactions, and profoundly affect community structure and stability. We investigated the threat of aliens on pollination networks in the species-rich lowlands of five Galápagos Islands. Twenty per cent of all species (60 plants and 220 pollinators) in the pooled network were aliens, being involved in 38 per cent of the interactions. Most aliens were insects, especially dipterans (36%), hymenopterans (30%) and lepidopterans (14%). These alien insects had more links than either endemic pollinators or non-endemic natives, some even acting as island hubs. Aliens linked mostly to generalized species, increasing nestedness and thus network stability. Moreover, they infiltrated all seven connected modules (determined by geographical and phylogenetic constraints) of the overall network, representing around 30 per cent of species in two of them. An astonishingly high proportion (38%) of connectors, which enhance network cohesiveness, was also alien. Results indicate that the structure of these emergent novel communities might become more resistant to certain type of disturbances (e.g. species loss), while being more vulnerable to others (e.g. spread of a disease). Such notable changes in network structure as invasions progress are expected to have important consequences for native biodiversity maintenance.