Summary1. Seed germination characteristics are often modified after seeds are ingested by frugivores. Factors that are intrinsic either to the plant or to the frugivore's digestive tract are responsible for the great variation observed in germination response. 2. Our objectives were to determine whether and how the seed germination patterns of five common western Mediterranean plant species are affected by seed passage through the guts of their major dispersers, and to elucidate the mechanism by which such patterns are changed. 3. We used captive birds ( Turdus merula and Sylvia melanocephala ) to obtain ingested seeds and compared their germination rate (speed) and germinability (final percent germination) with those of controls (uningested, pulp-removed seeds), controlling for seed age, size and source. Germination was monitored for 2 years in an experimental garden. We evaluated the possible changes in seed traits after ingestion by measuring weight and coat thickness, and by observing seed coat sculpture. 4. Rate of seed germination, but not germinability, changed in all species after gut treatment. The greatest effect was in Osyris , in which germination was much enhanced. A great acceleration of germination, which is likely to translate into a seedling size advantage, was also found in Asparagus . In the other three species tested, germination was slower for ingested than for control seeds. 5. For Rubus and Rubia seeds, we found a different germination response depending upon the frugivore species tested. A different degree of seed coat scarification caused by differences in gut retention time, chemical and/or mechanical abrasion probably account for such responses. 6. In three of the species ( Osyris , Rubia and Phillyrea ), seed weight decreased after gut treatment. Such weight loss was not caused by any change in coat thickness, but may have been because of the scarification and consequent alteration of the seed coat structure. 7. The five Mediterranean species studied germinate when rains are most likely to fall (mostly autumn and spring). The different speed of germination promoted by gut treatment within frugivores may increase the probability that seeds can recruit successfully at a given time and in a given place. 8. This study suggests that frugivores contribute to the heterogeneity in germination characteristics not only within plant populations but also within plant communities, each frugivore species having a particular effect on the seeds of each plant consumed.

Summary 1The fruit-colour polymorphism of Myrtus communis , a common Mediterranean shrub, is examined. We investigate whether frugivores affect the maintenance of the polymorphism, whether morphs differ in germination or seedling growth, and whether passage through frugivores' gut affects seed behaviour and seedling growth. 2 Blue berries are very similar in morphological traits and nutrient composition to the rarer white morph. Rates of fruit removal by birds, the main dispersers of this species, did not differ between morphs, suggesting that a colour preference is not involved in maintenance of the polymorphism. 3 Seeds of the two morphs showed the same germinability (final percentage germination) as well as similar rates of germination under controlled conditions (in growth chamber and greenhouse). Outdoors, seeds from blue berries tended to germinate slightly faster (which might give them an early advantage) but differences between morphs disappeared after several weeks of growth. 4 The germination of myrtle seeds is differently affected by passage through the digestive tract of birds, which appeared to significantly increase germinability, and of the carnivorous pine marten, Martes martes , which did not. The different seed retention time in the gut or the chemical composition of the food ingested along with the seeds may be responsible for such differences. 5 The detection of a positive effect of bird ingestion in outdoor conditions, but not in the growth chamber or in the greenhouse, demonstrates the importance of performing germination tests in the natural habitat. 6 Seed size, irrespective of morph, affects the response to passage through the bird gut. Large seeds, which are more rapidly ejected, and are thus less abraded, germinated at a similar speed to non-ingested controls. Variation in seed size within a single species should thus be considered in future studies.