Population response of Hemilepistus reaumuri to soil moisture patchiness

In an attempt to understand the factors affecting the distribution of the d esert isopod Hemilepistus reaumuri among patches with different soil moistu re, we studied its density and distribution in two patch types in relation to soil moisture. One patch type received natural rainfall, while the other was enriched by additional irrigation. We hypothesized that isopod densiti es in the two patch types would conform to the "ideal free distribution" mo del. Our results show that (1) the number of settlers are higher in the irr igated patches; (2) isopods demonstrate ideal free distributions only in lo w rainfall years; and (3) the overall effect of water-enriched patches is a decrease in population fluctuations. These results allow us to regard isop ods as patch selectors at the scale of the experimental patchiness. The imp lication of this study is that in fragmented areas, e.g., due to human dist urbance, water enrichment of the landscape in patches can create high quali ty patches with high abundance of isopods. These patches may stabilize popu lation size.