Pollination structures plant and nectar-feeding bird communities in Cape fynbos, South Africa: implications for the conservation of plant–bird mutualisms

Abstract

With the current global concerns about pollinators, relationships between species interactions and diversity are pivotal. If pollinator communities depend strongly on the diversity of flowering plants and vice versa, anthropogenic influences—whether positive or negative—on one partner will cause changes in the other. Here we ask whether nectarivorous bird communities are structured by resource abundance (Proteaceae nectar) or Proteaceae diversity at different spatial scales in the Cape fynbos of South Africa. On a small spatial scale, we sampled 34 one-hectare plots across the Cape Floristic Region (CFR) for flowering Proteaceae species, number of inflorescences, nectar volume, vegetation age, nectar-feeding bird abundance and species richness. At small scale, nectar—rather than vegetation structure or plant community composition—was the most strongly correlated to nectar-feeding bird diversity and abundance. On a landscape scale we investigated the spatio-temporal flowering patterns of ornithophilous Proteaceae throughout the CFR. Similar flowering patterns—with a winter floral abundance peak—were found throughout the region, but Protea, Leucospermum and Mimetes showed complementary flowering periods. At large spatial scales ornithophilous Proteaceae species richness is strongly correlated—more so than plant or floral abundance—to the nectar-feeding bird community. At large spatial scales resource diversity—and at a smaller scale resource abundance, shapes nectar-feeding bird communities. Providing high volumes of nectar sugar throughout the year is key to restore the nectar-feeding bird communities in small conservation areas.