Abstract
Following the southward shift of rainfall isolines in the Sahel at the end of the 1960s. Gerbillus nigeriae appeared in northern Senegal in the mid-1990s, and two resident Gerbillidae (Taterillus pygargus and Taterillus gracilis) subsequently declined. We investigated the causal role of the capacity to conserve water in such climate-related shifts in the distribution of these Gerbillidae by comparing the effects of a water-poor diet on the water-efflux rate (W-out) of freshly trapped adults pre-acclimatized to a water-rich diet. During the 12-day period of water restriction in all species, 30-50% of individuals became hyperactive and showed greater weight loss and higher W-out than the remaining inactive individuals. Such emergence of migratory strategists within populations could accelerate the expansion of G. nigeriae. On a water-poor diet, T. gracilis showed a lower capacity to conserve water (higher W-out) than T. pygargus and G. nigeriae, in both inactive (W-out = 44.5 +/- 1.8 vs 29.6 +/- 0.8 vs 27.4 +/- 0.7 ml kg(-0.82).day(-1), respectively) and hyperactive individuals (W-out = 60.4 +/- 1 vs 45.4 +/- 0.7 vs 44 +/- 0.8 ml kg(-0.82).day(-1), respectively). We propose that the capacity to conserve water accounted for both expansion of G. nigeriae and decline of T. gracilis, whereas competition between T. pygargus and G. nigeriae could account for the decline of T. pygargus. (C) 2011 Elsevier Ltd. All rights reserved.