ANT DISPERSAL OF CALATHEA (MARANTACEAE) SEEDS BY CARNIVOROUS PONERINES (FORMICIDAE) IN A TROPICAL RAIN FOREST

Two tropical herbaceous plant species, Calathea microcephala and Calathea ovandensis, exhibit morphological adaptations for seed dispersal by ants. In the field, 21 ant species are attracted to the arils of the seeds. Previously known as predatory carnivores, the ponerine ants Odontomachus laticeps, 0. minutus, Pachycondyla harpax, and P. apicalis carry the seeds toward their nests, behaving as though they were carrying prey. These ants remove the aril in the nest, and seeds without arils germinate more readily than seeds with arils. Ant foraging distances can account for seedling distributions. Myrmecochory may be far more common in tropical rain forests than has been previously suspected. THIS iS the first well-documented case of myrmecochory, seed dispersal by ants, for wet tropical rain forest floor herbs. Many cases of myrmecochory have been reported from temperate latitude mesic forests (see reviews in Ridley, 1930; van der Pijl, 1971; see examples Handel, 1976; Culver and Beattie, 1978). Only a few scattered reports come from the tropical latitudes, and, of these, the majority refer to ant-garden epiphytes high in the branches of trees (Ule, 1905, 1908; Bequaert, 1922; van Leeuwen, 1929; van Steenis and van Steenis, 1934; van der Pijl, 1951, 1955; Kleinfeldt, 1978). In subtropical Australia, a large number of myrmecochores have recently been found, but these were from dry sclerophyllous shrub vegetation, not from mesic forest herbs (Berg, 1976). The study of myrmecochory in a tropical forest bears on three evolutionary questions: 1) Does a mutualism such a myrmecochory imply an equivalent amount of evolutionary 1 Received for publication 15 May 1979; revision accepted 11 September 1979. We thank the following: Refugio Cedillo Trigos, Xavier Ramirez, Gabino Perez Garcia and other staff of the Estaci6n de Biologia Tropical de Los Tuxtlas, M6xico; Enrique Gonzalez, Dr. Jos6 Sarukhan, Dra. Ana Luisa Anaya, of the Instituto de Biologia, UNAM, M6xico; Diane L. Marshall and Dr. L. E. Gilbert, of the University of Texas, Austin; Dr. Stephen Bullock, of La Jolla, California; Dr. David C. Culver and Dr. E. Raymond Heithaus, of Northwestern University. Travel funds were provided by Special Dissertation Research Grant Committee, Northwestern University, awarded to C. C. Horvitz, and by a grant to A. J. Beattie and D. C. Culver (NSF DEB 76-02227). A pilot trip leading to this project was supported by a grant to Dr. L. I. Nevling, Field Museum of Natural History (NSF BMS 73-07061 A02). We thank him for his encouragement and Dr. Arturo G6mez-Pompa and field assistant Juan Ismael Calzada, of INIREB, Xalapa. adaptation for all species involved in the interaction (Vandermeer and Boucher, 1978; Gilbert, 1978)? 2) What are the effects of ant seed dispersal systems on germination and seedling distributions of plant populations (Grant, 1958; Sarukhan, 1974; McKey, 1975)? 3) What is the frequency of seed-ant interactions in tropical rain forests and how might such inconspicuous plant-animal interactions affect tropical ecosystem diversity (Farnsworth and Golley, 1973; Baker, 1973; GomezPompa et al., 1976; Howe, 1977; Gilbert, 1980)? This work is part of a study of the demographic consequences of myrmecochory in two herbaceous perennial plant species, Calathea microcephala (P. & E.) Koernicke sens. lat. and C. ovandensis Matuda (Marantaceae).2 These plants occur in primary high evergreen tropical rain forests (Gomez-Pompa, 1973) and in secondary forests in the region of Los Tuxtlas, Veracruz, Mexico. MATERIALS AND METHODS-Morphological adaptations for myrmecochory-Two hundred fifty individuals of C. microcephala and 150 individuals of C. ovandensis in permanent quadrats were monitored during the fruiting season, May-October, 1977-1978, in the field. The C. microcephala study site was in the Biological Reserve of the Universidad Nacional Autonoma de Mexico at Los Tuxtlas at an elevation of 160 m. There were two study sites for C. ovandensis, one at Los Chorros approaching Cerro Amarillo and the other at 2 Voucher specimens deposited at the Field Museum of Natural History, and the National Herbarium of Mexico (UNAM). Generous determinations and advice were provided by Dr. Helen Kennedy, Lyon Arboretum, University of Hawaii.