| Summary: | Global environmental changes, e.g. fragmentation of habitats and climate warming, are disrupting ecosystems worldwide. These man-induced environmental changes have caused a strong decline in biodiversity, which is hampering the provisioning of ecosystem services. For instance, flying insects and pollinators have declined, especially in industrialized countries, with potentially devastating consequences. However, the impacts of these changes are not easy to predict, since we are missing essential information on how the structure of plant-pollinator networks is actually related to their functioning. In this thesis, I examine such relations in the context of pollination services in the Arctic. The thesis work was mainly conducted in Zackenberg valley within the North-East Greenland national park with also a large scale study involving pollinator samples across the Arctic. In the absence of bees, muscid flies were found as the main pollinators of the Arctic and their presence increased the seed set of the flowers. Even though Arctic areas are generally species poor, the flower-visiting communities were surprisingly diverse. This is because majority of the Arctic insects are attracted by flowers and, thus, involved in the pollinator networks. In Zackenberg two thirds of the insects ever encountered in the area were found to be attracted by sticky flower mimics of a single flower species, mountain avens (Dryas octopetala×integrifolia). As Dryas also received majority of all the flower visits and its pollen contributed for 90% of the pollen carried by muscid flies, it could be considered a key species of the Arctic pollination networks. The flowering in the Arctic is concentrated on a short period after the snowmelt. The high flower densities during the early season cause strong competition on the pollinators and not all the flowers get pollinated. The abundant and attractive plant species, Dryas, gets practically all the flower visits which causes reduced seed set in the rare and less attractive species. During the ...
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