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Abstract: It has been suggested that lower rates of granivory
in South American warm deserts compared to their North 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.
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