Parthenocarpy (the production of seedless fruits) and abortion of reproductive structures at different developmental stages are important processes limiting female fecundity in Pistacia lentiscus (Anacardiaceae), a Mediterranean endozoochorous dioecious shrub. This paper tests (i) the effects of water and pollen as the ecological causes of abortion and parthenocarpy, (ii) the function of abortion and parthenocarpy regarding the uncertainty on resources and predispersal seed predation, and (iii) reviews the evolution of parthenocarpy across the phylogeny of the genusPistacia and the family Anacardiaceae. Using experimental manipulations, we examined the effects of pollen and water availability on female fecundity. The components of female fecundity were the four sequential developmental stages in the reproductive cycle: (i) flower survival after pollination, (ii) latent ovary survival, (iii) final-sized fruit survival, and (iv) seed viability. The survival of reproductive structures along the four developmental stages in response to pollination was highly variable. The survival of pollen-excluded flowers was negligible. Water addition increased the survival of reproductive structures in the first two developmental stages but this effect was lost in the other two stages. However, irrigation had a delayed effect, significantly increasing the number of viable seeds per number of flowers at the following reproductive season. The irrigated females significantly increased the percentage of viable seeds, whereas nonirrigated females did not. These data support the hypothesis that the adjustment of progeny size to the available resources is an individual feature inherent to the life history of each individual and therefore independent on the present resource level. This adjustment may have an adaptive value in relation to uncertainty of water availability. An advantage for parthenocarpy in terms of reducing seed predation was not found and it may be a nonadaptive plesiomorphic character within the genus Pistacia and within the family Anacardiaceae. A significant negative relationship was found between the rate of seed abortion and predispersal seed predation by wasps, suggesting that abortion reduces insect predation. In support of this hypothesis, we found that fruits with aborted seeds abscised in a lower proportion than expected, while fruits with seeds parasitized by wasps fell in a greater proportion than expected. Key words: abortion, parthenocarpy, predispersal seed predation, seed production.
Predispersal Seed Predation, Postdispersal Seed Predation and Competition in the Recruitment of Seedlings of a Native Thistle in Sandhills Prairie
