RESEARCH PAPER Pollination ecology of Disterigma stereophyllum (Ericaceae) in south-western Colombia L. Navarro 1 , P. Guitia´n 2 & G. Ayensa 1 1 Departamento de Biologı´a Vegetal, Facultad de Ciencias, Universidad de Vigo, Vigo, Spain 2 Departamento de Bota´ nica, Facultad de Farmacia, Universidad de Santiago de Compostela, Santiago de Compostela, Spain INTRODUCTION In the understorey of neotropical forests, hummingbird pollination is as frequent as that by medium to large bees (Bawa 1990). Although species of Ericaceae are prominent in tropical montane forests throughout the world, sur- prisingly little is known about their biology and ecology (Luteyn 1989). There have been relatively few studies of the breeding systems and pollination biology of neotropi- cal Ericaceae (Melampy 1987; Murray et al. 1987; Murcia & Feinsinger 1996; Navarro 1999, 2001; Busby 2000; Kra- emer 2001; Navarro et al. 2007). Within this family, many species show floral traits apparently adapted to humming- bird pollination (i.e. brightly coloured, long tubular flow- ers with inferior ovaries and abundant dilute nectar). Several studies of Ericaceae in Colombian montane forest have shown that species of this type are indeed mainly pollinated by hummingbirds (Snow & Snow 1980; Navar- ro 1999; Busby 2000). Other neotropical ericads show flo- ral traits apparently adapted to bee pollination (i.e. shorter, urceolate, white or light-coloured corollas) but, in spite of the commonness of such ‘bee pollination syn- drome’ species, their pollination has received little atten- tion (although see Snow & Snow 1980; Busby 2000). Within the genus Disterigma there are species that appear to conform to the bee pollination syndrome, hummingbird pollination syndrome, or both. However, floral characteristics do not always correspond well to the observed pollinator spectrum. For example, Disterigma alaternoides has small, white flowers that produce small Keywords Colombia; Ericaceae; hummingbird pollination; mixed pollination systems; pollination syndromes; pollinator efficiency. Correspondence L. Navarro, Departamento de Biologı ´a Vegetal, Facultad de Ciencias, Campus As Lagoas-Marcosende, Universidad de Vigo, 36200-Vigo, Spain. E-mail: lnavarro@uvigo.es Editor M. Ayasse Received: 21 November 2007; Accepted: 21 December 2007 doi:10.1111/j.1438-8677.2008.00059.x ABSTRACT Several authors have recently expressed doubts that the ‘pollination syn- dromes’ as usually expressed are an adequate description of correlated suites of floral characters, or that they adequately describe evolutionary or ecologi- cal associations of plants with pollinators. Disterigma stereophyllum is a neotropical Ericaceae with floral characteristics intermediate between the ‘entomophilous’ syndrome and the ‘ornithophilous’ syndrome: the corolla is short, white and urceolate, but flowers produce large amounts of dilute nec- tar. We studied the pollination ecology of this species in south-western Colombia, and found it to be pollinated almost exclusively by humming- birds at our study site. Two hummingbird species were responsible for about 75 of visits. Despite the fact that nectar standing crop remained more or less constant throughout the day, visit frequencies were highest in the morning and declined throughout the day. Pollinator efficiency, measured as the number of pollen grains deposited on a virgin stigma by each visitor after one visit, did not differ among the species of hummingbirds, but was lower for a nectar-robbing bird, Diglossa albilatera. This species does not contact the surface of the stigma during nectar robbing, but can produce some self-pollination indirectly because it shakes branches vigorously while piercing the flower. These findings indicate a need for further studies of neotropical Ericaceae in order to elucidate whether floral visitors of species like D. stereophyllum fluctuate through time or space, and whether floral characteristics reflect a compromise between such different visitors, or a transitional stage between pollination syndromes, or some other possibility. Plant Biology ISSN 1435-8603 512 Plant Biology 10 (2008) 512–518 ª 2008 German Botanical Society and The Royal Botanical Society of the Netherlands