Response of endemic afroalpine rodents to the removal of livestock grazing pressure

The Bale Mountains of Ethiopia represent the world’s largest continuous extent of afroalpine habitat. With a peak combined density of over 8000 individuals/km, the endemic giant mole rat Tachyoryctes macrocephalus, Blick's grass rat Arvicanthis blicki and the brush-furred mouse Lophuromys melanonyx are the dominant wild herbivores within this ecosystem and may be affected by the presence of high densities of domestic livestock. The purpose of this study was to establish whether these endemic rodent populations could respond to the removal of grazing pressure inside three 0.25 hectare livestock exclosures (paired with grazed control plots) and to determine whether such response was mediated through concomitant changes in the vegetation structure. We hypothesised that livestock grazing negatively affects endemic rodent populations through competition or increased predation risk and we predicted an increase in rodent biomass following the removal of grazing pressure. We found no evidence of rodent populations responding to the removal of livestock after fourteen months. The short-term nature of the experimental design, environmental fluctuations and the ecosystem’s inherent stochasticity may explain the apparent lack of a significant response. However, while this study is inconclusive, it emphasises the need for more long-term experimental investigations to assess the effects of domestic grazers on vegetation and on dependent communities. The effects of rapidly increasing livestock numbers in the Bale Mountains will require continued close monitoring of vegetation and endemic animal communities as the afroalpine is altered by external biotic and abiotic forces [Current Zoology 57 (6): 741–750, 2011].