COMMUNITY STUDIES IN POLLINATION ECOLOGY IN THE HIGH TEMPERATE ANDES OF CENTRAL CHILE. I. POLLINATION MECHANISMS AND ALTITUDINAL VARIATION

Pollination mechanisms and pollinators are reported for a total of 137 species (75% of the non-abiotically pollinated flora) as they occur at three altitudinal levels (subandean scrub: 2,200-2,600 m; cushion-plant zone: 2,700-3,100 m; subnival feldfield: 3,200-3,600 m) in the Andean (alpine) zone on the Cord6n del Cepo (33? 17'S) in central Chile as part of community oriented research in reproductive biology in the high temperate Andes of South America. Only around 4% of the species studied failed to be visited by potential pollinators. Hymenopterans (principally bees) are important pollinators of 50% of the biotically pollinated flora, butterflies of 24% and flies of 46%. Other vectors include beetles, moths, and hummingbirds. An estimated 17% of the flora is anemophilous. Bee species-richness, specialist feeding, and melittophily reach maxima in the subandean scrub; thereafter, bees diminish rapidly in number, with bees pollinating only 13% of the subnival flora as contrasted with 68% of the subandean flora. Although fly and butterfly species-richness also decline with increasing altitude, the proportions of species pollinated by these vectors actually increases. High-altitude populations of melittophilous species with broad altitudinal ranges are invariably serviced by fewer bee species as compared with lower populations. The rich bee fauna at the lower end of the Andean zone in central Chile appears to have resulted from upward colonization from that of the subtending lowland Mediterranean sclerophyllous woodland vegetation. Altitudinal variation in pollination spectra is discussed in relation to contrasting life history characteristics and different modes of thermoregulation in the insect groups involved. RECENT STUDIES on the energetics of foraging (e.g., Heinrich, 1974), nectar and pollen con'Received for publication 22 September 1980; revision accepted 4 December 1980. 2 Departamento de Biologia, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile. 3Department of Botany, Boston University, Boston, Massachusetts, USA. Many students, but especially Paulina Uslar and Michaelangelo Trevalli, are thanked for their collaboration with field work. Hymenopterans were identified by Dr. H. Toro, Depto. de Zoologia, Universidad Catolica, Valparaiso, lepidopterans by Dr. J. Herrera, Fac. de Ciencias, U. de Chile, Santiago and dipterans by Dr. M. Etcheverry, Fac. de Ciencias, U. de Chile, Dr. Raul Cortes, Universidad del Norte, and Dr. Jorge Artigas, Secci6n de Entomologia, Depto. de Zoologia, Universidad de Concepci6n, all in Chile and without whose collaboration this research would have been impossible. We are especially grateful to SDCACI, U. de Chile for providing a special travel grant to R. Primack and to Dr. P. H. Raven, Missouri Botanical Garden, who provided much unavailable literature, and with whom many useful discussions were held during the writing of this paper. The Club Deportivo, Universidad de Chile provided logistic support and Hoteles Portillo granted permission to circulate on high Andean access routes, for which we are most appreciative. This research was supported by Grant No. B388/803 to M.T. K.A. by SDCACI, Universidad de Chile and forms part of MAB-6 (UNESCO/UNEP 1105-77-01). stituents (e.g., Baker and Baker, 1979) and relationships with flowering phenology (e.g., Stiles, 1978; Whelan and Burbidge, 1980) have added new dimensions to research in pollination biology. The implications of these studies, nevertheless, have yet to be thoroughly explored at a community level, and as Faegri and van der Pijl (1979) recently stated in reviewing progress in pollination ecology, "until now the evolution of community pollination spectra has only been touched on. " In high-mountain plant communities above timberline, opportunities for growth are restricted to the spring and summer months, and, in temperate regions, prevented during the remainder of the year by low temperatures and associated snow cover. Flowering as a consequence must be limited to a relatively short period of the year, which tends to decrease in length as the upper vegetational limit is approached. Increased low-temperature stress with altitude also affects the distribution and abundance of insects (Mani, 1962). Thus predictably, plant-pollinator relationships might change both quantitatively and qualitatively with altitude. From the work of early naturalists (e.g., Muller, 1880), and more recently that