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Bipartite graph of the butterfly-plant network of Porto Santo.
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Porto Santo (Madeira Archipelago) is a relatively old (11.1 to 14.3 Ma) and small volcanic island in the Atlantic Ocean. The main part of the island is characterised by semiarid climate and xeric vegetation, while the higher altitudes show subhumid conditions. So far, 11 butterfly species (Papilionoidea) have been detected on Porto Santo. The occur...
Context in source publication
Context 1
... bipartite graph of the butterfly-plant network of Porto Santo (Fig. 2) shows the flower-visiting butterfly species on the left-hand side and the visited plant species on the right-hand side, both connected by interaction links. The butterfly-plant network is asymmetric: seven butterfly species versus 15 plant ...
Citations
... Previous investigations on the interactions between plants and their insect pollinators in Macaronesia have mostly been carried out in the Canary Islands, e.g., [14,27,28], with several other contributions from the Azores archipelago [28][29][30][31]. In the Madeiran archipelago, much fewer studies were carried out, usually being taxonomically biased and consisting mostly of lists of species associations resulting from unstandardized sampling [28,29,[32][33][34][35]. Following the study of pollination networks on five oceanic islands (including Flores in the Azores), Olesen et al. [36] identified the prevalence of endemic species with a very wide pollination niche, which were coined as super generalists. ...
The study of flower visitor behavior and pollen transport dynamics within and between plants can be of great importance, especially for threatened or rare plant species. In this work, we aim to assess the flower visitor assemblage of the Madeiran endemic Echium candicans and evaluate the performance of the most common visitors through the analysis of their foraging behavior and pollen loads. The flower visitor assemblage of E. candicans is diverse, including several insect groups and the endemic lizard Teira dugesii, but bees are the most common visitors. In general, large bees (Amegilla quadrifasciata, Apis mellifera, and Bombus spp.) had the highest average visitation rates (>18 flowers/min) and their pollen loads had higher percentages of homospecific pollen (>66%) when compared with butterflies and hoverflies. The honeybee (Apis mellifera) and two bumblebees (Bombus terrestris and B. ruderatus) were the most efficient flower visitors of E. candicans, but their foraging behavior seems to favor geitonogamy. Other visitors, such as butterflies and the small bee Lasioglossum wollastoni, may have a complementary role to the honeybee and bumblebee species, as their high mobility is associated with fewer flower visits on each plant and may promote xenogamy. Two non-native bees (A. mellifera and B. ruderatus) are important flower visitors of E. candicans and may contribute mostly to self-pollination rendering the endemic plant more vulnerable to inbreeding effects.
The aim of this study was to analyse wild bee-plant interactions in Madeira Island and construct a network structure covering the largest parts of the island and most altitudes and habitat types. The interaction data were sampled at 179 localities from 1989 to 2012 mainly by the authors; additionally, data from the collections of the Laboratório Agrícola da Madeira, Camacha (ICLAM) and the Museu de História Natural do Funchal, Madeira, Portugal, were used. Twelve wild-bee species (the complete species pool of permanently established Madeiran wild-bee species) were collected or observed on 81 plant taxa (belonging to 30 plant families). The total dataset from Madeira Island includes 637 data points of bee-plant interactions. We assigned the data set to the main thermotypes – infra- / thermo-Mediterranean zone as well as meso-Mediterranean / temperate zone – and constructed two networks. In contrast to most of the mainland networks of temperate and Mediterranean ecosystems with more wild-bee than plant species, the bee-plant networks demonstrate high asymmetry, with many more plant than bee species. This phenomenon has also been documented, e.g., in Porto Santo (Madeira Archipelago). Wild-bee species and plant species were highly interconnected within the network, showing that even under difficult and strong climatic conditions with unequal resource availabilities, there were enough alternatives for obtaining food resources. Ten of the wild-bee species are euryanthic, with only two species (the introduced Hylaeus pictipes and the endemic Andrena maderensis) showing stenanthy. The high individual numbers and euryanthic behaviour of most wild-bee species met the precondition for network stability. The plant families with the highest importance as food resources are in the orders Asteraceae (51%), Brassicaceae (14%), Fabaceae (8%) and Boraginaceae (8%). These offer different flower types (actinomorphic, zygomorphic, Asteroideae and Cichorioideae types) and a variability of flower types for wild-bee species of different body sizes and foraging behaviour. Similar to the results of the bee-plant network of Porto Santo, most of the foraged plant species were endemic or native species. Introduced and cultivated plant species mainly showed minor importance. We found no disturbances of the network by the introduced masked bee Hylaeus s. signatus and the probably introduced bumblebee Bombus r. ruderatus. Differences and similarities between the bee-plant networks of Madeira Island (infra- / thermo-Mediterranean zone) and the corresponding areas of the much older island Porto Santo (xeric- / infra-Mediterranean zone) are discussed in this paper.