Floral attraction and flower visitors of a subcanopy, tropical rainforest tree, Fontainea picrosperma

Abstract

Flowering plants in tropical rainforests rely heavily on pollen vectors for successful reproduction. Research into pollination systems in tropical rainforests is dominated by canopy species, while subcanopy plant–pollinator interactions remain under-represented. The microclimate beneath the rainforest canopy is characterized by low light levels and is markedly different from the canopy environment that receives more light energy. We studied the floral attractants and floral visitors of a dioecious, subcanopy tree, Fontainea picrosperma (Euphorbiaceae), in the Wet Tropics bioregion of northern Queensland, Australia. We found that wind pollination is rare and male and female flowers do not produce nectar. Female flowers are likely pollinated due to their perceptual similarity to pollen-offering male flowers. Female flowers had the same scent profile as male flowers, and floral scent was an important floral attractant that acted to regulate pollinator behavior. The two most abundant scent compounds present in the floral bouquet were benzyl alcohol and 4-oxoisophorone. These compounds are ubiquitous in nature and are known to attract a wide variety of insects. Both day-time and night-time pollinators contributed to successful pollen deposition on the stigma, and diurnal flower visitors were identified from several orders of insects including beetles, flies, predatory wasps, and thrips. Fontainea picrosperma is therefore likely to be pollinated by a diverse array of small insects. Synthesis. Our data indicate that F. picrosperma has a generalist, entomophilous pollination syndrome. The rainforest subcanopy is a distinctive environment characterized by low light levels, low or turbulent wind speeds, and relatively high humidity. Female flowers of F. picrosperma exhibit cost-saving strategies by not producing nectar and mimicking the smell of reward-offering male flowers. Insects opportunistically forage on or inhabit flowers, and pollination occurs from a pool of small insects with low energy requirements that are found beneath the rainforest canopy.