With the rising threat to insect pollinators and the upcoming pollinator crisis, it is important to know how pollinators contribute to pollen transfer. The contributions of individual pollinator taxa to pollen transfer depend both on their abundance and on how much pollen each individual can carry, with overall importance being a multiplication of these two values. Here, we quantified pollen load across a diverse spectrum of insect pollinator taxa and variation in their abundance over 11 years. We found that, while variation in pollen load was relatively small among pollinator taxa (compared to relatively high variability among individuals within each insect taxon), the visitation levels changed significantly over the years, resulting in a high degree of variation in pollinator contributions to pollen transfer of each insect taxon at the community level. Thus, we conclude that the overall importance of pollinator taxa for pollen transfer is determined further by their abundances than by their taxon-specific capability for carrying various pollen loads. As the insect abundances vary over time and may change dramatically from year to year, our results highlight the importance of diverse and species-rich pollinator communities, as the population decline of one pollinator can be buffered by an increase in another pollinator taxa.

• Keywords
• conspecific pollen, pollen load, pollen transfer, pollination, pollinator abundance, pollinators,
• Publication type
• Journal Article MeSH

Species extinctions undermine ecosystem functioning, with the loss of a small subset of functionally important species having a disproportionate impact. However, little is known about the effects of species loss on plant-pollinator interactions. We addressed this issue in a field experiment by removing the plant species with the highest visitation frequency, then measuring the impact of plant removal on flower visitation, pollinator effectiveness and insect foraging in several sites. Our results show that total visitation decreased exponentially after removing 1-4 most visited plants, suggesting that these plants could benefit co-occurring ones by maintaining high flower visitor abundances. Although we found large variation among plant species, the redistribution of the pollinator guild affected mostly the other plants with high visitor richness. Also, the plant traits mediated the effect of removal on flower visitation; while visitation of plants which had smaller inflorescences and more sugar per flower increased after removal, flower visitors did not switch between flower shapes and visitation decreased mostly in plants visited by many morpho-species of flower visitors. Together, these results suggest that the potential adaptive foraging was constrained by flower traits. Moreover, pollinator effectiveness fluctuated but was not directly linked to changes of flower visitation. In conclusion, it seems that the loss of generalist plants alters plant-pollinator interactions by decreasing pollinator abundance with implications for pollination and insect foraging. Therefore, generalist plants have high conservation value because they sustain the complex pattern of plant-pollinator interactions.

• MeSH
• Plant Dispersal MeSH
• Species Specificity MeSH
• Extinction, Biological * MeSH
• Insecta physiology   MeSH
• Flowers MeSH
• Animal Migration physiology   MeSH
• Pollination physiology   MeSH
• Pilot Projects MeSH
• Food Chain * MeSH
• Feeding Behavior physiology   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Hoverflies (Diptera: Syrphidae) are among the most important pollinators, although they attract less attention than bees. They are usually thought to be rather opportunistic flower visitors, although previous studied demonstrated that they show colour preferences and their nectar feeding is affected by morphological constraints related to flower morphology. Despite the growing appreciation of hoverflies and other non-bee insects as pollinators, there is a lack of community-wide studies of flower visitation by syrphids. The aim of this paper is to provide a detailed analysis of flower visitation patterns in a species rich community of syrphids in a Central European grassland and to evaluate how species traits shape the structure of the plant-hoverfly flower visitation network. We found that different species varied in the level of specialisation, and while some species visited a similar spectre of flowers, others partitioned resources more strongly. There was a consistent difference in both specialisation and flower preferences between three syrphid subfamilies. Eristalinae and Pipizinae were more specialised than Syrphinae. Trait-based analyses showed that relative flower visitation (i) increased with plant height, but most strongly in Eristalinae; (ii) increased with inflorescence size in small species from all three subfamilies, but was independent of inflorescence size in large species of Eristalinae and Syrphinae; and (iii) depended on flower colour, but in a subfamily-specific way. Eristalinae showed the strongest flower colour preferences for white flowers, Pipizinae visited mostly white and yellow flowers, while Syrphinae were less affected by flower colour. Exploration of the structure of the plant-hoverfly flower visitation network showed that the network was both modular and nested. We also found that there were almost no differences in specialisation and relative visitation frequency between males and females. Overall, we showed that flower visitation in syrphids was affected by phylogenetic relatedness, body size of syrphids and several plant traits.

• Keywords
• Foraging, Hoverflies, Plant-pollinator interactions, Pollination, Pollination networks, Species traits,
• Publication type
• Journal Article MeSH