Competition between foragers and food producers on the Botletli River, Botswana

The immigration of food-producing groups into areas occupied by hunters and gatherers must have been a common occurrence in prehistory. How were the hunter-gatherers affected by this? I describe here two groups of Kalahari Basarwa ('Bushmen'), one living along the flood plain of the lower Botletli river, the other occupying the savanna a short distance away from the river. These two groups differed in subsistence and social organisation and were affected by immigrant herders and farmers in strikingly different ways. Today the Basarwa of the flood plain are wealthy cattle owners, whereas those of the savanna are poor and have few or no cattle. How and why did the two groups respond so differently to the same competitive threat?