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In this paper the effect of herbivory on the seed production of Moricandia moricandioides (Cruciferae), an annual species living in arid habitats of southeastern Spain, is analysed. Firstly, the flowering and fruiting phenology and the composition and structure of the pollinator guild is described, in order to compare the overall effect of mutualistic species vs. that of antagonistic species on M. moricandioides seed production. The loss of female reproductive success due to each herbivore species attacking the plant is then quantified, in an attempt to differentiate the effects on plant seed production of each herbivorous species. The results indicate that only antagonistic organisms interacting with M. moricandioides influenced the female fitness of this plant species. In fact, pollinator abundance or activity did not correlate with the number of seeds dispersed by the plants. In addition, of all the herbivore species, only sheep activity significantly influenced seed production of M. moricandioides individuals, the effect of the remaining crucivorous herbivores being cancelled by the stronger herbivory of sheep. The results of this study suggest that herbivory by sheep, in addition to decreasing the seed production of M. moricandioides, could be an important determinant of the current distribution pattern of this crucifer species on the ramblas of the Baza basin. (C) 1996 Academic Press Limited