The tall, annual grass Sorghum intrans is a dominant component of the understorey of the eucalypt savannas in the seasonally wetdry tropics of north-west Australia. Its seeds provide a large potential seed-fall resource for granivores at the end of the rainy season (April) until the first storms of the next rainy season (September-November), when all remaining viable seeds germinate. I measured the proportion of viable seeds of S. intrans removed from the soil seed-bank during the dry season. In addition, experimental seed caches were exposed for 18-24 hr at four times during the dry season under various treatments to estimate the proportion of seeds removed by invertebrates, and to examine the preferences for different classes of seeds (sound, empty, scorched). Almost all of the granivory of S. intrans was due to an ant, Meranoplus sp., which was not observed to harvest seed of any other species. Meranoplus sp. acted as a seed predator, rather than a disperser. Birds and mammals were insignificant granivores of S. intrans. On average, the viable seed bank was depleted by ca 60 percent over the dry season through death and predation, and I estimate that at least half of this loss was due to granivory by Meranoplus sp. The activity of Meranoplus sp. appeared to be patchy both in space and time. The ants preferentially removed sound seeds as compared with empty seeds which looked superficially similar but which lacked a well-formed grain; there was no selection for viable seeds within the sound seed category. I infer that this level of depletion of the seed-bank is not normally detrimental to the persistence of S. intrans because of compensatory, density-dependent seed production. However, Meranoplus sp. has the potential to remove, locally, the entire viable seed-bank of S. intrans. SEED PREDATORS CAN STRONGLY INFLUENCE THE population dynamics of a species by depleting its seedbank significantly, and thus restricting opportunities for recruitment. Examples from the literature cover a range of life-forms, from trees (Boucher 1981, Pickard 1982, De Steven & Putz 1984, O'Dowd & Gill 1984, Wellington & Noble 1985), shrubs (Heithaus et al. 1982, Louda 1982), a biennial forb (Grieg-Smith & Sagar 1981), and grasses and forbs (Campbell 1982, Carroll & Risch 1984, Davidson, et al. 1984). The importance of seed predation is likely to be greatest for annual plants which lack any seeds with a long-term dormancy and thus have purely transient seedbanks. The indigenous annual Sorghum spp. which dominate the understorey of large areas of the tropical savannas of northern Australia possess this characteristic-their entire seed-banks germinate during each rainy season (Andrew & Mott 1983). These species abruptly and synchronously shed their large, awned seeds (ca 0.013 g, 2.3 x 11.2 mm, excluding the 72 mm awn) at the end of the annual rainy season (March-May), thus providing a substantial food resource for granivores over the ensuing dry season (ca 100-900 seed m-2) (Andrew & Mott 1983). Ants commonly can be seen harvesting this seed, although this activity has been little studied (Mott & McKeon 1977). How significant is this seed removal for the population dynamics of these annual species which have transient seedbanks? This paper reports a study into the granivory of seeds of Sorghum intrans at a site near Darwin, Northern Territory. The study's aim was to assess the proportion of the seed-bank of S. intrans removed by granivores, to discover the proportion of granivory due to invertebrates, and to examine their preference for different classes of seeds. MATERIALS AND METHODS STUDY SITE.-This study was conducted at Thorak (12025'S, 130058'E), 10 km E of Darwin, N.T. (Andrew and Mott 1983) at a site where harvester ants were observed to be active. The site lies in the semi-arid tropics, and has a single 4-month rainy season from December through March, followed by a rain-free dry season from May-September. Its mean annual rainfall is 1634 mm. The site has gravelly yellow earths supporting a woodland community, much depleted by cyclone 'Tracy' in 1974, of Eucalyptus tetrodonta and E. miniata with a herbage layer comprising mainly the grasses Sorghum intrans (dominant), Aristida browniana, and Plectrachne pun-