The impact of floral parasitism in two neotropical hummingbird-pollinated plant species [Aphelandra golfodulcensis and Justicia aurea]

Flowers of two neotropical wet lowland forest species, Aphelandra golfodulcensis and Justicia aurea (both Acanthaceae), were visited by both pollinators and floral parasites. Both species were pollinated by the larger hermit hummingbirds and pierced by other bird species and insects (bees and ants). In addition, Trigona sp. bees took pollen from Aphelandra flowers without effecting pollination. The effect of parasitism depends upon a number of factors including frequency of parasitism, impact of parasites on the availability of floral rewards and the response of pollinators to parasitized flowers. Nectar and pollen parasites affected the vast majority of flowers produced in the two study populations: over 90% of flowers of both species had been pierced by noon and more than 90% of Aphelandra flowers had been visited by pollen collecting bees by mid-morning. Pollen parasites frequently caused severe damage to the style as well: about 40% of Aphelandra flowers daily were damaged in this way. Flowers which had been pierced contained less nectar than flowers which had been visited only by pollinators if at all. Visits by nectar parasites left an average 3.5 μ l of nectar more than visits by long-billed hummingbird pollinators. Nectar removed by flower visitors was never fully replaced nor did nectar depletion stimulate subsequent production. Pierced flowers subsequently produced less nectar than legitimately visited flowers such that visits by nectar parasites had the two-fold effect of removing nectar and reducing total nectar secretion. In response to decreased nectar availability due to parasitism, pollinators may partially or completely avoid visits to these populations or may visit more such nectar-poor flowers in order to satisfy their energy requirements. These two very different responses would result in decreased or increased reproductive success, respectively Pollen parasitism of Aphelandra flowers may be of particular significance since if pollen is limiting, even increased visits by pollinators would not result in greater reproductive success. Circumstantial evidence suggests that in both populations floral parasitism has adverse effects on fruit and seed set levels. A result of the explosion of successional communities due to human disturbance may be rather significant changes in the biotic interactions which are especially important in animal-pollinated plant species.