Pollinator conservation in the Anthropocene

Pollinators play a key role in ecosystems, ensuring the reproduction of most cultivated and wild flowering plant species. However, recent studies showed that pollinator communities are rapidly changing due to multiple causes, with potential effects also on the fundamental ecosystem service they provide. Through the chapters of my thesis, I will analyse how the factors shaping the abundance, diversity and distribution of pollinators in landscapes, and thus determine their thriving or decline, affect both managed and wild pollinators. After a brief introduction (Chapter 1), I investigated the effects of landscape composition and seasonality on the properties of pollen collected by managed honey bees, in particular on pollen diversity (Chapter 2) and pollen contamination by pesticides (Chapter 3). We highlighted how landscape composition strongly affected both pollen features and in particular how a high amount of semi-natural habitats in landscapes helped both to increase the heterogeneity of pollen collected by honey bees and to minimise contamination by pesticides. In the next chapter, I focused on managed pollinators, which can negatively impact wild pollinator communities when introduced into new ecosystems (Chapter 4). We examined how potential competition between managed honey bees and wild pollinators was influenced by the functional traits of both pollinators and the plants they forage on. We highlighted that plant communities characterised by high functional richness could help mitigate potential competition between managed and wild pollinators by providing alternative resources on which wild pollinators can forage and that pollinators characterised by functional traits similar to those of the honey bee were more prone to potential competition. I then focused on the effects of climate on pollinators (Chapter 5). Using a space-for-time substitution approach, we explored how increasing temperatures affected wild bee communities in an urban environment. We found that higher temperatures were generally associated with a higher abundance and species richness of wild bees, but they also led to a homogenisation of wild bee community traits, favouring a few traits such as small body size and polylectic diet. Last, I analysed how two pollinator-friendly measures, i.e., habitat restoration and habitat enhancement for pollinators, affected pollinator diversity and ecosystem multi-functionality (Chapter 6). We sampled wild pollinators and a large number of ecosystem services, using which we calculated two indices of ecosystem multi-functionality, in sites belonging to three habitat types with a gradient of flower coverage. We found that while habitat restoration from intensive to semi-natural habitats benefited both pollinators and multiple ecosystem services, habitat enhancement for pollinators did not affect ecosystem multi-functionality. In conclusion, the results obtained from my thesis could help develop targeted strategies for the conservation of both wild and managed pollinators. We found that semi-natural areas play a key role in supporting pollinators, that honey bees may pose a threat to specific categories of pollinators, and that rising temperatures will lead to drastic changes in pollinator communities. We also showed how the functional traits of both plants and pollinators have a strong influence on pollinator responses to the factors that threaten their survival. Finally, we pointed out how conservation measures for pollinators may – or may not – also impact other fundamental ecosystem services. It is therefore clear that multiple factors must be considered in order to get a clear picture of how pollinator communities are changing and what we can do to slow, stop or reverse their decline. Species conservation is a complex science, and further studies are needed to investigate the potential effects of interactions between drivers threatening managed and wild pollinators in the Anthropocene.