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

Abstract

We analysed two potential effects of post‐dispersal seed predation on recruitment of the wild olive tree (Olea europaea var. sylvestris), a Mediterranean bird‐dispersed tree: (a) the limitation of abundance and distribution of seedlings after dispersal, and (b) the selection of certain seed characteristics of the recruited plants. An observational approach was used to compare seed rain among microhabitats, and how it was affected by seed predation. The relation of microhabitat, scrub density, and seed size with predation risk was explored by a field experiment. Seed density ranged from 0 seeds/m2 in open places to 93.2 seeds/m2 under O. europaea. The overall predation rate was low, as shown in the observational approach (35%). The mean percentage of predation in the experimental approach was 51%, ranging across 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 medium and small ones (57% and 55%, respectively). Finally, seed density near seed depots did not increase their probability of being detected by rodents or the predation rate. Although predation rates were low, wild olive seeds could be frequently found by rodents due to their spatial ubiquity and local abundance. Together with the efficient foraging strategy of predators (92% of experimental seed depots were found), this allowed a widespread post‐dispersal predation, but it did not modify the relative distribution of seeds 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 and (2) mice did not seem to limit the number of recruits. Finally, our results indicate that, as a consequence of seed size preferences of rodents, large seeds have a higher probability to survive post‐dispersal predation. Thus, seed size may be a key trait to determine the identity of the future recruits in the wild olive tree, at least affecting the characteristics of the seeds that reach the soil seed bank.