The discussion about the impact of pastoralists on ecosystems has been profoundly shaped by Hardin's tragedy of the commons that held pastoralists responsible for overgrazing the range. Research has shown that grazing ecosystems are much more complex and dynamic than was previously assumed and that they can be managed adaptively as commons. However, proponents and critics of Hardin's thesis continue to argue that open access to common-pool resources inevitably leads to a tragedy of the commons. A longitudinal study that we conducted of pastoral mobility and primary production in the Logone floodplain in the Far North Region of Cameroon suggest that open access does not have to lead to a tragedy of the commons. We argue that this pastoral system is best conceptualized as an open system, in which a combination of individual decision-making and coordination of movements leads to an ideal-free type of distribution of mobile pastoralists. We explain how this selforganizing system of open access works and its implications for theories of management of common-pool resources and our understanding of pastoral systems.

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A raft of recent studies has highlighted a major decline in large mammal populations in many of Africa's protected areas. A recent continent-wide assessment represented a major step forward also in terms of quantifying the decline on a regional basis, but fell short in its sampling and analysis. In this paper, a way out of the “black box” of large mammal declines in Africa's protected areas is formulated, with the aim of assisting in the preparation of further assessments in the future. First, large mammal assessments are categorized, highlighting the importance of using and sometimes juxtaposing peer-reviewed sources. The importance of the length of time series of large mammal counts is stressed, allowing one to distinguish between natural variation (especially rainfall) and human-induced changes. Setting reference dates, such as 1970, often gives biased results, showing the need to interpret large mammal population assessments in a historic context as well. This holds true particularly for West-Central Africa, which has experienced a considerable decline in rainfall since 1970. Building on a framework that connects herbivore physiology and behavior with environmental gradients, examples are given to explain some striking observed changes. The declines in Africa's protected areas are not limited to large mammals, but have also been observed for large birds of prey. Assessments of large mammal populations should be accompanied by the identification of proximate drivers of change, for which a framework is suggested in this paper. To conclude, some suggestions for countering the declines in large mammal populations are presented.