Early effects of rodent post-dispersal seed predation on the outcome of the plant-seed disperser interaction

We analysed two potential effects of post-dispersal seed predation on recru itment of the wild olive tree (Olea europaea var. sylvestris), a Mediterran ean bird-dispersed tree: (a) the limitation of abundance and distribution o f seedlings after dispersal, and (b) the selection of certain seed characte ristics of the recruited plants. An observational approach was used to comp are seed rain among microhabitats, and how it was affected by seed predatio n. The relation of microhabitat, scrub density, and seed size with predatio n risk uas explored by a field experiment. Seed density ranged from 0 seeds /m(2) in open places to 93.2 seeds/m(2) under O. europaea. The overall pred ation rate was low, as shown in the observational approach (35%). The mean percentage of predation in the experimental approach was 51%, ranging acros s microhabitats between 28% and 88%. It was higher in dense scrub patches ( 67%) than in sparse ones (33%), and lower for large seeds (42%) than for me dium and small ones (57% and 55%, respectively). Finally, seed density near seed depots did not increase their probability of being detected by rodent s or the predation rate. Although predation rates were low, wild olive seed s could be frequently found by rodents due to their spatial ubiquity and lo cal abundance. Together with the efficient foraging strategy of predators ( 92% of experimental seed depots a ere found), this allowed a widespread pos t-dispersal predation, but it did not modify the relative distribution of s eeds among microhabitats. Thus? in our study, the seed dispersal pattern of the wild olive tree was not reshaped by post-dispersal predation. because (1) rodents did not alter significantly its initial spatial distribution an d (2) mice did not seem to limit the number of recruits. Finally, our resul ts indicate that, as a consequence of seed size preferences of rodents, lar ge seeds have a higher probability to survive post-dispersal predation. Thu s. seed size may be a key trait to determine the identity of the future rec ruits in the wild olive tree, ai least affecting the characteristics of the seeds that reach the soil seed bank.