Climate change and human activities are causing insect pollinator declines in many parts of the world. This has direct consequences for human food production, since many crop species require insect pollination to produce seeds_ and fruits (termed “pollinator dependence”). Pollination can also improve the quality of crop harvests, such as larger and/or more nutritious fruits. However, declining pollinator populations can negatively impact food chains in nature too. Many wild flowering plants also rely on insect pollination to produce fruits, which feed other animals. In the UK, ivy fruits feed some of our best-loved birds, including song thrushes and winter visitors like the fieldfare. Previous research suggests that ivy shows pollinator dependence – if this is true, then pollinator declines can reduce the food supply for many fruit-eating animals. However, the extent of such dependence and whether pollination affects the quality of fruit remains unknown.
To address this missing knowledge, we investigated the importance of pollination to ivy fruit production in terms of quantity and quality, as well as how that can affect the feeding choices of animals. We conducted this study in a mixed woodland-meadows nature reserve and a botanical garden in Cambridge. We manipulated the level of pollination received by ivy plants and found that the quantity and quality of fruit depends strongly on insect pollination. Without the help of insect pollinators, the production of fruits in ivy dropped dramatically by 90%, and the fruits were also smaller. Monitoring the survival of ivy fruits revealed that animals can prefer well-pollinated fruits. At the woodland site, over 99% of fruits which received extra pollen were eaten, whereas over half of the unpollinated fruits remained untouched. Hence, the initial level of pollination also influences animal feeding choices.