Herbivory in rocks and the weathering of a desert.

Two species of snail, Euchondrus albulus and Euchondrus desertorum, eat endolithic lichens growing under the surface of limestone rocks in the Negev Desert, Israel. This unusual type of herbivory has the unexpected and major impact of weathering this rocky desert at a rate of 0.7 to 1.1 metric tons per hectare per year. The biotic weathering contributes to the process of soil formation at a rate that is similar to wind-borne dust deposition. These findings demonstrate that herbivores can have a significant regulatory impact on ecosystem processes, even in cases where the total amount of primary production consumed is small.