Flowering Phenology and Diversity in Tropical Bignoniaceae

Abstract

Central American Bignoniaceae show five distinct patterns of flowering phenology. Four of these phenol6gical types characterize different bee-pollinated species. Only the generalized cornucopia strategy is employed by temperate Bignoniaceae. In the tropics this strategy is also prevalent and is often associated with a seasonal sequence of flowering by related species. The more specialized phenological strategies employed by many tropical species of Bignoniaceae are viewed as making possible differential and essentially contemporaneous attraction of similar pollinators from the same limited pollinator resource. The high diversity of tropical Bignoniaceae appears to be facilitated by use of a variety of phenological strategies by the different species. It is suggested that such mechanisms may be an important factor in maintaining increased tropical diversity in other groups of plants. DIFFERENCES IN flowering phenology among Central American Bignoniaceae illustrate an overlooked mechanism for maintenance of high species diversity in tropical plant communities. The ecological importance of these differences in phenology is in making possible effective and often contemporaneous sharing by numerous plant species of a limited pollinator resource. Evolutionary diversification of floral morphology in the Bignoniaceae has, of course, given rise to genera employing most of the potential pollen vectors available in a tropical community (Gentry 1972, 1973). But although bats (in Parmentiera, Crescentia, Dendrosicus), hummingbirds (in Mawrtinella), hawkmoths (in Tanaecium), and butterflies and small bees (in Tynnanthus and Arrabidaea florida) are the principal pollinators of some Bignoniaceae, the majority of the 76 species occurring naturally in Costa Rica and Panama are pollinated by large and medium-sized bees, especially female euglossines. In some bee-pollinated species additional morphologic specializations further restrict potential pollen vectors as in Amphilophium where pseudocleistogamous flowers which never open spontaneously can be entered only by the strongest members of the apifauna (Megachile, large anthophorids, presumably xylocopids). However, most bee-pollinated species of Bignoniaceae secure their requisite pollinators by different strategies of flower production rather than morphologic differentiation.