Woodrats and Cholla: Dependence of a Small Mammal Population on the Density of Cacti

Abstract

In the deserts of Southern California, stands of jumping cholla cactus (Opuntia bigelovii) are usually inhabited by desert woodrats (Neotoma lepida). The density of woodrats is obviously correlated with the density of cacti. On our study area, an alluvia fan in Joshua Tree National Monument, 80% of the variability in the density of woodrats could be attributed to variation in the density of cacti. The turnover of the woodrat population (mortality and replacement) apparently was greatest in areas of low density of cacti. The dependence of woodrat populations on the density of cholla may be attributed to the fact that the cacti provide most resources required by the woodrats; food, water, materials, for den construction, and a means of avoiding predation. Woodrats also are abundant in some habits where there is little or no cactus of any king, so that their dependence on cholla is not obligate.