Fruit losses and fruit removal in Olea europaea var. sylvestris Brot. (Oleaceae)

摘要

We analyzed several aspects of the reproductive biology of wild olive ( Olea europaea var. sylvestris . Brot.) related to seed dispersal. The importance of several fruit fates (the way and condition in which fruits leave the tree) is considered in two different habitats, one of which was surveyed in two consecutive years. We distinguished the following fruit fates: (a) consumption by avian seed dispersers (fruit removal), (b) loss due to different biotic (e.g. birds and insects), abiotic (e.g. weather) and plant-controlled factors (e.g. abscission), and (c) fruits remaining on the tree by the end of the season. The ranking of importance of each fruit fate did not differ between habitats, and was similar among individual trees, although the net valúes of each fate were highly variable among trees. On the average, in the two habitats and seasons the plant investment in fruit crop yielded a low reward in terms of fruit removal success (between 16 and 33 % of the total fruit crop). This was attributable to different factors in the two habitats; in one of them, wild olive fruit crop satiated the scarce avian seed dispersers, whereas in the other, interspecific competition for avian seed dispersers with Phyllirea latifolia probably diminished wild olive removal success. Total fruit losses increased during the second season (from 8 to 40 % of the total fruit crop). However, it did not set a limit to the total amount of seeds being dispersed. Fruit losses were mainly caused by abiotic factors rather than by biotic ones. The percentage of fruits (both unripe and ripe) falling apparently healthy from the branches was higher than the percentage damaged by climatic factors (desiccated and frozen fruits). Among damaging biotic agents (pests and birds), the most frequent one was the larvae of the fly Dacus oleae , followed by birds (both dispersers that drop the fruit while handling and fruit predators) and, accounting for a negligible percentage, the larvae of the moth Prays oleae . By the end of the season, in both plots, a high percentage of the fruit crop remained on the trees (up to 75 % in the first year in one plot). This, together with the high variability between individuals in removal success, suggests a strong intraspecific competition for avian seed dispersers. In conclusion, although removal success in the studied populations was low, our results indicate an important role for dispersers in the success of the fruiting phase as part of the wild olive reproductive cycle.