Cumulative Effects on the Reproductive Output of Pistacia terebinthus (Anacardiaceae)

This study identifies the factors that influence the reproductive output (number of viable seeds dispersed) of Pistacia terebinthus (Anacardiaceae), examines the magnitude and variability of their effects, and considers how plant traits affect the relative importance of each factor in reducing reproductive potential. Pre-dispersal reproductive losses were measured in a total of 28 individuals from anthesis to seed dispersal. Post-dispersal seed predation was estimated as well by placing seeds in different locations and checking them periodically. A total of eight factors were found to reduce plant reproductive potential during the pre-dispersal phase. Ordered according to the importance of their effects these factors were: abortion of flowers and latent ovaries, abortion of seeds, fruit dryness (mainly caused by hemipterans that suck the fruit pulp), parthenocarpy (production of empty seeds), consumption of viable fruits by non-legitimate seed dispersers, fruit damage by psyllids, seed damage by chalcidoid wasps, and fruit damage by fungi. There was much inter-individual variability in the effects of all those factors. That variation, however, was in most cases independent of the plant traits examined (plant size, fecundity, distance to males, flowering synchrony, peak date of fruit ripening). The most relevant associations were found between plant fecundity and (1) proportion of wasp-damaged seeds (larger fruit crops experienced greater seed predation by these insects) and (2) proportion of fruits removed by non-legitimate seed dispersers (smaller fruit crops with greater proportions of viable seeds had higher bird predation rates). Also, plants that had most fruits ripen in early September had more viable seeds removed by non-legitimate dispersers than those that had most fruits ripen in late September. A key factor analysis showed that factors intrinsic to the plant, such as flower and ovary abortion and seed inviability, accounted for low among-plant variation in total reproductive losses, even though their relative contribution to such losses was great. Extrinsic factors such as fruit or seed damage by animals accounted for a low reproductive loss but for great among-plant variation in the number of viable seeds dispersed, and appeared to act as selective agents on plant fecundity. Post-dispersal seed predators (mainly field mice, chaffinches, and ants) removed a significant proportion of the seeds placed in different locations where birds can drop them, indicating that seedling recruitment in a given site is largely determined by the abundance of these animals at that site.