PREDATOR - PREY RELATIONSHIPS - RODENT - SNAIL INTERACTIONS IN THE CENTRAL-NEGEV DESERT OF ISRAEL

We investigated the effects of increasing rodent (Acomys cahirinus and Gerbillus dasyurus) predation efficiency on their population density and the population of their prey, the desert snail (Trochoidae seetzenii). The study was carried out on a rocky hillslope in the Central Negev Desert, Israel. Rodent predation on snails is limited by the number of shelters for rodents in the area. In most natural conditions, more shelters are found on the upper than on the lower slope. We introduced artificial shelters along the slope. We then censused the number of rodents, snails, and of eaten snails for five years. In the presence of artificial shelters the predation efficiency of rodents (number of snail eaten per rodent) increased. The number of rodents also increased and the number of snails decreased on the experimental plots relative to control plots. We suggest that the persistence of the snail-rodent system is due to spatial variation in the relative importance of direct prey-predator relations and the indirect effects of snail immigration to the slope and presence of protective shelters for the rodents. Our study supports recent work indicating that in a prey-predator system, in addition to direct predation, the heterogeneity of the environment and predation risk while foraging, affect both the behavior and the density of the predator and the prey.