Australian Journal of Ecology (1982) 7,63-67 Seed dispersal in a cycad, Macrozamia riedlei ALLAN H. BURBIDGE* ROBERT J. WHELAN+ Botany Department and ^Zoology Department, University of Western Australia, Nedlands, Australia 6009 Abstract The influence of animals on patterns of seed dispersal has not been well explored, despite the importance of seed dispersal in plant population biology. Furthermore, the exploitation of animals as dispersal agents has been considered one reason for the replacement of gymnosperms by angiosperms in the Cretaceous. We studied seed dispersal in a cycad, Macrozamia riedlei, and showed that in the absence of animals, ripe seeds drop directly beneath the parent not more than 40 cm from the base. Several animak eat the fleshy outer integument of the seeds, and possums (Trichosurus vulpecula), transport seeds up to 24 m from the parent. The postdispersal positioning of seeds gave a log density-log distance relationship of ^ = 7,20 — 2.85\ fr^ = 0.96, N = 17). Effective local dispersal may have contributed to the persistence of cycads in the world flora for the last 200 million years. Introduction Apart from van der Pijl's (1957) report of bat dispersal of Cycas rumphii seeds, little is known of seed dispersal in cycads. Indeed, there are few studies on the influence of animals on seed dispersal patterns even in angiosperms (Harper 1977, p. 34). There is increasing interest in this "Present address: Rotamah Island Bird Observatory, Box 75, Paynesville, Australia 3880 ^Present address: Zoology Department, University of Horida, Gainesville, Florida 32611, USA. 0307-692X/82/0300-0063 $02.00 © 1982 Blackwell field, however, particularly in tropical areas (e.g. Howe 1980; Hubbell 1980). Attempts have been made to model seed dispersal patterns (e.g. Harper 1977; Hubbell 1980), but more studies are needed in a range of habitats before valid generalizations can be made. This study is a description of seed dispersal in Macrozamia riedlei (Gaud.) Gardner, a cycad with a widespread distribution in south-western Australia. Study site and methods Generally, Macrozamia riedlei has no above-ground stem, the strobili (cones) being borne just above the ground. Although the seeds are large and heavy (5 cm long, 40 g fresh weight), they are often found some distance from the nearest, mature, female plant. With or without their red, fleshy outer integument, seeds are readily seen on the sandy, coastal-plain soils. Observations were made at the University of Western Australia Marsupial Breeding Station, 25 km south of Perth (32° 10' S, 115° 50' E). This is an area of jarrah (Eucalyptus marginata) and Banksia woodland on sandplain (Seddon 1972) and includes a large, natural population of Macrozamia riediei. Densities of Macrozamia plants at the study site were quite variable, in some areas exceeding 200 plants/ha. Periodic fires are the only common disturbance and Macrozamia responds by reproducing in the second year after fire (Baird 1977). In order to determine the extent of seed dispersal in the absence of animals, a large, female Macrozamia with two unopened strobili was completely enclosed with 4 cm wire mesh. The enclosure had a diameter of about 1.5 m, ensuring that it did not interfere with the seeds. When all the seeds had fallen from the plant, their distances from the base were measured. Scientific Publications