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It has been suggested that lower rates of granivory in South American warm deserts compared to their Noah American counterparts arose from a reduction of seed reserves in the former owing to the extinction of argyrolagid marsupials. We measured seed reserves in two habitats of the central Monte Desert in an attempt to detect such seed decline, but to no avail. After moderate rainfall, maximum seed standing crops reached 16,000 and 23,000 seeds m(-2) in shrublands and open forests, respectively. Under the canopy of trees and shrubs there were 19,000 and 37,000 seeds m(-2); whereas in exposed areas there were c. 10,000 seeds m(-2) in both habitats. Seed banks in other South American semi-arid areas showed similar values. Total grass seeds as well as those presumably preferred by ants also seem to be similar in both continents. Hence, granivory in South America, as has been already reported for Australia, is lower than in North America in spite of the great similarity of seed bank sizes. Moreover, argyrolagids were unlikely seed-hoarding granivores, therefore some other reason than argyrolagid extinction should be sought to explain the lack of specialized seed-eating mammals, and the smaller overall seed consumption rates in South American deserts. (C) 1997 Academic Press Limited.