PREDATION BY RODENTS AND THE DISTRIBUTION AND ABUNDANCE OF THE SNAIL TROCHOIDEA-SEETZENII IN THE CENTRAL NEGEV DESERT OF ISRAEL

Trochoidea seetzenii exhibits a regular pattern of spatial distribution in the C Negev drainage basin: high density at the Wadi bottom, gradually decreased density toward the top, and very low density at the hill tops. Rocky hill sides often have feeding tables, recognized by accumulation of many broken snail shells. Rodents bring snails to the feeding tables where they crack and eat them in the relative safety of shrub or rock cover. Feeding tables are concentrated at the upper rocky part of the slopes, which also provide natural burrows for the rodents, ie low risk areas for the rodents against their own predators. The authors constructed artificial shelters along an entire slope. Predation pressure on snails in these experimental plots increased gradually along the slope being highest at the top of the hill. They also collected data from a long term manipulation of shelters (27 yr) are found that the snail density is significantly and drastically reduced relative to a control plot. Snail density along the hillside is also correlated with number of shrubs and availability of egg laying sites. Predation, shrubs, and laying sites determine the basic distribution pattern of the snails in the area. -from Authors