www.oikosjournal.org OIKOS Oikos 1413 –––––––––––––––––––––––––––––––––––––––– © 2019 e Authors. Oikos © 2019 Nordic Society Oikos Subject Editor: Paulo Guimaraes Jr Editor-in-Chief: Dries Bonte Accepted 17 May 2019 128: 1413–1423, 2019 doi: 10.1111/oik.06053 e structure of pollination networks, particularly its nestedness, contain important information on network assemblages. However, there is still limited understanding of the mechanisms underlying nested pollination network structures. Here, we investigate the role of adaptive interaction switching (AIS), island area, isolation, age and sam- pling effort in explaining the nestedness of pollination networks across ten Galápagos Islands. e AIS algorithm is inspired by Wallace’s elimination of the unfit, where a species constantly replaces its least profitable mutualistic partner with a new partner selected at random. To explain network structures, we first use a dynamic model that includes functional response of pollination and AIS, with only species richness and binary connectance as input (hereafter the AIS model). ereafter, other explanatory variables (isolation, area, age and sampling effort) were added to the model. In four out of ten islands, the pollination network was significantly nested, and predictions from the AIS model correlated with observed structures, explaining 69% variation in nest- edness. Overall, in terms of independent contribution from hierarchical partitioning of variation in observed nestedness, the AIS model predictions contributed the most (37%), followed by sampling effort (28%) and island area (22%), with only trivial contributions from island isolation and age. erefore, adaptive switching of biotic interactions seems to be key to ensure network function, with island biogeographic factors being only secondary. Although large islands could harbour more diverse assemblages and thus foster more nested structures, sufficient sampling proves to be essential for detecting non-random network structures. Keywords: adaptive rewiring, island biogeography, mutualism, nestedness, pollination network, sampling effort Introduction Islands often harbour highly endemic community assemblages that are largely constrained by biogeographical factors such as island area, age and degree of isolation (MacArthur and Wilson 1967). Besides these physical constraints, climate and human Fine-tuning the nested structure of pollination networks by adaptive interaction switching, biogeography and sampling effect in the Galápagos Islands Chinenye A. Nnakenyi, Anna Traveset, Ruben Heleno, Henintsoa O. Minoarivelo and Cang Hui C. A. Nnakenyi (https://orcid.org/0000-0003-1009-5181) ✉ (assumpta@sun.ac.za, chui@sun.ac.za), H. O. Minoarivelo and C. Hui, Centre for Invasion Biology, Dept of Mathematical Sciences, Stellenbosch Univ., Matieland 7602, South Africa. CH also at: Mathematical Biosciences Group, African Inst. for Mathematical Sciences, Cape Town, South Africa. – A. Traveset, Mediterranean Inst. of Advanced Studies (CSIC-UIB), Global Change Research Group, Esporles, Mallorca, Balearic Islands, Spain. – R. Heleno, Centre for Functional Ecology, Dept of Life Sciences, Univ. of Coimbra, Coimbra, Portugal. Research