Ecological imbalance as floral resource supply outstrips pollinator demand: half the pollen and nectar produced by the main autumn food source, Hedera helix, is uncollected by flower-visiting insects

1. Declines in floral resources, pollen and nectar, are considered one cause of pollinator decline. However, the supply and demand of floral resources can vary temporally. In Britain, autumn has been suggested as a period of relative resource abundance due to the flowering of ivy (Hedera helix), a common native plant, combined with fewer insects active during this season. Here we directly quantified the proportion of pollen and nectar produced by ivy, the primary autumn food source, which is uncollected by the flower-visiting insect community.
2. We quantified the proportion of nectar produced but uncollected by comparing the mass of nectar sugar accumulated in insect-accessible versus inaccessible ivy flowers and by surveying the presence of wasted, crystalised, nectar on flowers. Pollen wastage was quantified by comparing pollen counts on anthers at the start of anthesis versus anthers dropped from ivy flowers.
3. Approximately half the floral resources, 59% nectar and 44% pollen, were uncollected by the flower-visiting insect community in autumn. As ivy flowers supply most of the available nectar and pollen in autumn, our results show that a large proportion of all floral resources are wasted in autumn.
4. Our results are the first to show that a season can be characterised by a large surplus of floral resources relative to collection by flower-visiting insects. These results demonstrate the importance of considering seasonal variation in floral resources in the conservation of bees and other flower-visiting insects.

1. 花卉资源的减少，包括花粉和花蜜的短缺，被认为是传粉者数量下降的一个原因。然而，花卉资源的供需在时间上可能存在波动。在英国，由于常绿植物常春藤（Hedera helix）的盛开，秋季被认为是一个相对资源丰富的时期，这一现象与该季节昆虫活动减少的现象相伴随。在本研究中，我们直接量化了常春藤产生的花粉和花蜜的比例，常春藤是该季节的主要食物来源，而访问花朵的昆虫群落并未收集这些资源。
2. 通过比较昆虫可接触与不可接触的常春藤花朵中积累的花蜜糖质量，以及调查花朵上浪费的、结晶化的花蜜存在情况，我们量化了未被收集的花蜜比例。通过比较花药在花蕾初现时的花粉计数与从常春藤花朵中落下的花药数量，我们量化了花粉的浪费情况。
3. 在秋季，约有一半的花卉资源，即59%的花蜜和44%的花粉，未被访问花朵的昆虫群落所收集。鉴于常春藤花朵提供了秋季大部分可用的花蜜和花粉，我们的结果表明，在秋季，大量花卉资源被浪费。
4. 我们的研究首次表明，一个季节可以以其相对花蜜资源过剩相对于昆虫访问者的收集量为特征。这些结果证明了在保护蜜蜂和其他访问花朵的昆虫时，考虑花卉资源的季节性变化的重要性。