Habitat selection along an environmental gradient: Theoretical models withan example of Negev Desert rodents

We present a set of models of density-dependent habitat selection along an environmental gradient. The models are based on the assumption of ideal-fre e distribution and use an approach similar to Morris' isodar analysis techn ique. It was assumed that habitats along a gradient differ either qualitati vely (efficiency of resource acquisition) or quantitatively (resource abund ance) or in both parameters. Depending on the distribution of resource abun dance and habitat quality along a gradient, the models predict density-inde pendent or density-dependent habitat distribution with or without density-d ependent habitat shifts The models were tested using data on a desert roden t community of the central Negev Desert, Israel. In six of the nine rodent species (Gerbillus dasyurus, G. gerbillus, G. henleyi, Meriones crassus, Ac omys cahirinus and A. russatus), direct estimations of habitat breadth and position fit well the predictions of one of the models based on density rel ationships. Of these nine species, four (Jaculus jaculus, Gerbillus dasyuru s, G. gerbillus and Mus musculus) were found to be density-independent habi tat selectors, four (Meriones crassus, Psammomys obesus, Acomys cahirinus a nd A. russatus) were density-dependent habitat selectors and one (Gerbillus henleyi) was a density-independent habitat selector in winter and a densit y-dependent habitat selector in summer.