GAZELLE HERBIVORY AND INTERPOPULATION DIFFERENCES IN CALCIUM-OXALATE CONTENT OF LEAVES OF A DESERT LILY

We investigated the abundance and distribution of calcium oxalate crys tals in the leaves of wild populations of a Negev desert lily, Pancrat ium sickenbergeri, in relation to herbivory. Three species of herbivor es are known to eat the leaves of this lily: a small antelope, the dor cas gazelle Gazella dorcas, a moth larva Polytella cliens, and a land snail Eremina desertorum. All three species eat only those parts of th e leaves where calcium oxalate raphides are absent, suggesting that it is an effective defensive chemical. We compared the abundance of raph ides in three isolated lily populations that differed only in the amou nt of gazelle herbivory. Within lily populations, we found neither siz e-related differences in raphide abundance nor differences in raphide abundance between plants that had previously been partially consumed a nd those that had not. We found significant differences among lily pop ulations in the amount of calcium oxalate crystals in their leaves, wi th the most raphides being found in the population suffering most herb ivory, fewer in a population with intermediate herbivory, and the leas t in a population without gazelle herbivory. Additionally, sand sample s showed no differences among populations in two major nutrients (nitr ogen and phosphorus) but significantly more calcium in the sand in the population without herbivory. Thus, calcium oxalate abundance in the leaves of Pancratium sickenbergeri is not constrained by resource avai lability but rather appears to have been selected for by gazelle herbi vory. This is the first study to show the effects of selection on calc ium oxalate production in a wild plant by a wild herbivore.