The future of the savannah ecosystems: ecological islands or faunal enclaves?

Abstract

Summary

Various savannah reserves are examined to determine whether they are likely to lose substantial numbers of large herbivores if they become isolated. The relationship between the number of ungulate species and the size of each reserve is examined and compared to predictions established from existing island biogeographic studies. In the case of the savannah reserves, no significant relationship was found. However, when the data were re-analysed for reserves of similar habitat, significant though low z-values of 0.04 and 0.08 were established. For discrete ecosystems rather than reserves a steeper z-value of 0.14 was found.

It is suggested that the z-value for the savannah ecosystems is lower than the typical value of 0.22 for other land mass islands because of the ubiquitous distribution of most large herbivore species and their long history of co-evolution.

The significance of island biogeographic theory to the design of nature reserves is limited, at least in the savannahs. Most of the variation in the number of species in areas which can be practically established as reserves can be explained by habitat and landscape diversity. Whether the savannah reserves became faunal islands will be decided by political and economic policies and practices rather than the principles of ecological design. The design of reserves in the past is considered to have been based on sound ecological principles in most cases, even though these were not recognized at the time.