Fruit Structure in Two Neotropical Mistletoes and Its Consequences for Seed Dispersal

This study tests the hypotheses that (1) mistletoes with hard exocarps have lower fruit predation levels than mistle toes with soft exocorps, and (2) fruits with hardExocarPS have higher seed dispersal success than fruits with softExocars.

Abstract

Many species of tropical mistletoes have fruits with either hard exocarps visited by a particular taxon of birds, like the New World euphonias and the Old World flowerpeckers, or soft exocarps visited by a greater diversity of bird species. A comparative study of two species of Neozropical mistletoes in the Republic of Panama suggests that predation might be important in selecting for these fruit characters. Fruits of Phoradendron quadrangulare with hard exocarps have minimal predispersal predation but suffer from postdispersal predation due to clumped deposition of seeds. Fruits of Oryctanthus alveolatus with soft exocarps suffer less postdispersal predation of seeds but have high predispersal fruit loss. HEMIPARASITIC MISTLETOES OCCURRING IN TROPICAL regions of the world are mostly dispersed by birds (Kuijt 1969). Often a single taxon of frugivorous birds are implicated in seed dispersal (Ali 1931; Docters van Leeuwen 1954; Davidar 1978, 1983). Observations in India and in Central America indicated that fruits dispersed only by specialist birds have hard exocarps that are discarded by the birds. The pulp and seed are swallowed, and the seeds are excreted in slimy masses by the bird (Davidar 1978, 1983). The seeds often stick onto a branch, the ideal substrate for these hemiparasitic plants. Other mistletoe species in these areas were dispersed by a wider variety of bird species (Davidar 1978, 1983). These species had fruits with soft exocarps, and the seeds were either discarded prior to ingesting the pulp or swallowed whole and excreted or regurgitated. The seeds were more often voided in smaller clumps by these birds (Davidar 1983). This study tests the hypotheses that (1) mistletoes with hard exocarps have lower fruit predation levels than mistletoes with soft exocarps, and (2) fruits with hard exocarps have higher seed dispersal success than fruits with soft