Post-fire flowering enhances pollinator visitation and may reduce florivory and nectar robbing in sunbird-pollinated plants

Abstract

Tubular flowers optimize pollen placement and typically attract specialized pollinators. However, their unique shape also makes them susceptible to some insects and birds that either consume or damage flowers (florivory) or access nectar by damaging the floral tube without pollinating (nectar robbing), reducing visits from legitimate pollinators. However, in areas where vegetation has burned within two years, flowers may be less affected by florivory and nectar robbing due to reduced abundance or satiation of these exploiters after a fire. This study examined florivory and nectar robbing in three bird-pollinated plants (Watsonia pillansii, Erica cerinthoides, and Satyrium carneum) and their effects on sunbird visitation rates in early-stage and transitional-stage post-fire fynbos vegetation in the Cape Floristic Region, a Mediterranean-type ecosystem, South Africa. In 42 plots (10 × 10 m) in three nature reserves, we recorded the number of flowers with robber holes, florivory damage, and intact flowers. We also monitored insects, sunbirds, and their behaviour, and quantified pollinator visitation rates. Bird pollinator visits were significantly more frequent in early- than transitional-stage vegetation for all three species. Florivory was significantly lower in early-stage vegetation for W. pillansii and S. carneum, but did not differ for E. cerinthoides. Robbing rates were significantly lower in early-stage vegetation for W. pillansii and E. cerinthoides, but showed the opposite pattern in S. carneum. Bird pollinators tend to avoid plants with higher florivory across all species, but nectar robbing impacts on pollinator visits per flower per hour varied among plant species. These behaviours, varying among plant species, could be influenced by floral traits such as corolla stickiness. Furthermore, the differences observed in florivory rates could also be influenced by the floral display size in the study species. Future studies could elucidate how floral traits and display size influence florivory and nectar robbing rates, especially after a fire.