Investigating species associations and pollination networks for the wild heathers of Great Britain

On the backdrop of drastic declines in both heathland habitats and insect volumes, this study identifies wild heather and bumblebee co-occurrences and wild heather-pollinator interaction networks within current heathland habitats in Great Britain. Many wild heather-bumblebee mutualisms have been identified, which provide insights into which species which may be most at risk of decline and extinction in the event of continued environmental and anthropogenic pressures. Ecosystem network keystone heather species are identified as Calluna vulgaris, Erica cinerea and Erica tetralix. Keystone Bombus species are identified as Bombus jonellus, Bombus terrestris, Bombus vestalis, Bombus lapidarius and Bombus hypnorum. Of the keystone species, Bombus jonellus and Erica tetralix are considered most at threat of extinction. In the case of Bombus jonellus this is due to the reliance on nectar and pollen within heathland environments and in the case of Erica tetralix this is due to a limited range of pollinators which provide a clear non-incidental pollination service to the dwarf shrub. In wild heather-pollinator networks, Erica ciliaris is also considered at risk due to its strong reliance on Bombus terrestris / Bombus lucorum agg. and limited pollinator network size, which partly may be due to a general requirement for a relatively long proboscis to access nectar in the deep corolla of that species. The natural hybrids Erica x watsonii and Erica x williamsii are already rare and may become extinct if their parent plants distributions were subject to further contractions. Andrena fuscipes and Colletes succinctus, due to their oligolectic preference for ericaceous dwarf shrub pollen, may also be at higher risk of extinction than more generalist pollinator species. It is recommended that further research is undertaken on the degree of decline of the range of wild heather species and their associated pollinators in order to best target emerging conservation needs with a view to pr