Can sheep replace indigenous antelope as seed dispersers in the Kalahari?

The Southern Kalahari Duneveld is an arid savannah, which has been used for permanent stock farming since around 1900. Farming with high numbers of animals has led to changes in the vegetation which have been associated with excessive grazing and trampling. To determine whether altered seed dispersal could be an alternative or additional explanation, we investigated how replacing antelope with sheep affects seed dispersal. We determined the dispersal potentials of plant species by various vectors using standardized experiments and studied the variation of dispersal potential along a grazing intensity gradient and among different habitats. Wind dispersal potential was low, but diaspores of many plant species were well adapted to dispersal by water. Biotic long-distance dispersal potentials were relatively high and varied between sheep and antelope: the species of plants dispersed differed, as did the number of seeds transported and the time of year that seeds were dispersed in. The importance of zoochory and the differences found between antelope and sheep dispersal suggest that dispersal is affected by a change of animal type. Thus, sheep can not replace antelope as seed dispersers. Therefore, sustainable grazing management or restoration efforts should benefit from seed input of sensitive species where antelope are rare. (C) 2012 Elsevier Ltd. All rights reserved.