The pollination network of a native Hawaiian coastal plant community is dominated by non-native insects
Little is known regarding pollination webs involving island coastal plants and pollinators, and the roles that non-native flower visitors may play in these interaction networks. Plant-pollinator observations collected in March 2008 and 2009 were used to describe the pollination network for Ka’ena Point, one of Hawaii’s best-conserved coastal communities.
The network includes 15 native plant species, 2 native insect species, and 27 non-native insect taxa, forming 121 interactions. Network connectance is 28.8% and weighted nestedness is 31.0, which is similar to other dry habitat, island networks. The network’s structure has a compartment of generalized pollinators followed by a gradient pattern of more specialized pollinators. Nearly all plant species interact with two or more generalist pollinators and a variable number of specialists. Small, non-native bees (Lassioglossum, Ceratina), wasps (Proconura), and flies (Tachinidae) were responsible for 81.7% of the flower visits and visit five plant species not visited by native bees. The two native visitors, Hylaeus anthracinus and H. longiceps, (both proposed as threatened/endangered) belong to a radiation of > 60 endemic species in Hawaii’s only genus of native bees. Hylaeus spp. (especially females) provided 18.3% of the flower visits, foraging on many species and at high frequencies, including the endangered Scaevola coriacea and Sesbania tomentosa. In Hawaii’s coastal habitat, non-native insects provide most of the flower visitation to native plants. However, the two remaining native Hylaeus species are still important pollinators to many native plants on which they rely for nectar and pollen resources.