Do introduced honeybees affect seed set and seed quality in a plant adapted for bird pollination?
Aims Worldwide, evidence suggests that exotic pollinators can disrupt plant mating patterns. However, few studies have determined if pollination by the honeybee Apis mellifera (the world's most widely introduced pollinator) reduces offspring quality when compared with pollination by native birds. The Australian Proteaceae provides an excellent opportunity to test the impact of honeybees in pollination systems that are adapted to birds and non flying mammals. Methods We compared the frequency of flower visitation and foraging behaviour of birds and insects within seven populations of Banksia ericifolia. Banksia ericifolia is hermaphroditic and has large nectar rich, orange inflorescences typical of bird and mammal pollinated species. For a subset of the study populations, we compared the quality of seed produced via an exclusion treatment (that only allowed invertebrates to access flowers) with an open pollination treatment (potentially visited by mammals, birds and invertebrates) by measuring seed weight, germination rates (T50) percent germination, seedling height after 14 days since the emergence of the cotyledon and time to emergence of the cotyledon. Important Findings Apis mellifera was the only apparent insect pollinator and the most frequent flower visitor, while the open treatment inflorescences were also frequently visited by avian pollinators, primarily honeyeater species. The foraging behaviour of honeybees and honeyeaters showed striking differences that potentially affect patterns of pollen transfer. Honeybees made significantly greater proportions of within cf. among plant movements and only 30% (n 48) of honeybees foraged for pollen (nectar foragers carried no pollen) whilst all birds were observed to contact both stigmas and anthers when foraging for nectar. Despite these fundamental differences in behaviour, there was little effect of treatment on seed set or quality. Our data show that while honeybees appear to alter patterns of pollen transfer within B. ericifolia populations, they do not impact reproductive rates or performance of early life stages.