Comparative Demography of Three Namib Desert Rodents: Responses to the Provision of Supplementary Water

Abstract

This study was designed to test the hypothesis that increased dietary water intake is a critical factor in desert rodent reproduction. Populations of three Namib Desert rodent species ( Desmodillus auricularis, Gerbillurus paeba , and Rhabdomys pumilio ) were monitored by mark-and-recapture live-trapping on two study areas, one of which served as a control. On the other, rodents were continuously provided with sources of drinking water. Populations of G. paeba and R. pumilio grew rapidly following rains in early 1974, and reached peak population sizes in September or October 1974. Reproduction in both of these species on the control area showed marked declines during the hot, dry months of September to December, January, or February. Both G. paeba and R. pumilio showed marked responses to the increased availability of water on the experimental area, as evidenced by a greater number of pregnancies and higher proportions of lactating females, and an extension of the breeding season longer into the hot, dry portions of the year. The effect of increased water availability on these species was most pronounced during times of the year when water stress might be expected to be greatest. Population growth in D. auricularis proceeded in a much less seasonally restricted manner than in the other two species, and peak population sizes were not reached until February or March 1975. Breeding intensity in this species on the control area declined only slightly during portions of the year when R. pumilio and G. paeba were relatively inactive reproductively. On the experimental area, D. auricularis showed no consistent reproductive or numerical response to increased water availability. The relationship between response to the experimental provision of water in these species and the seasonality of demographic patterns is discussed.