In Eastern Africa contrasting ecological zones within relatively short distances encourage economic specialisations which are reliant upon one another. Connections between different economic groups are facilitated by a variety of institutionalised networks that encourage the movement of both goods and people across boundaries. The role of livestock as essential capital ensures a strong impetus to increase agricultural production for exchange while, at the same time, the need to acquire livestock through ties to the pastoral community ensures that certain agriculturalists are confined to relatively limited areas at the margins of pastoral zones. In contrast to traditional models of agricultural development, the shift to intensive techniques may not be a radical departure from earlier practices, but rather much less labour intensive and gradually developed, aimed at expanding and improving natural zones of high productivity. This situation may have been exasperated by climatic fluctuations while lineage systems of social organisation encourage the localised marginalisation of politically unified descent groups and the development and expansion of large-scale agricultural works.