HERBIVOROUS MAMMALS AS SEED DISPERSERS IN A MEDITERRANEAN DEHESA

Endozoochorous seed dispersal by herbivorous mammals has been verified repeatedly and its possible influence on the structure and function o f herbaceous communities has been suggested. Quantitative studies, how ever, are lacking in the field of seed dispersal via the dung of herbi vore guilds in little-altered environments. The present paper analyses seed dispersal via rabbit, fallow deer, red deer and cow dung in a Me diterranean dehesa (open woodland used for hunting and ranching) durin g the seeding season. Dung seed content was determined by the glasshou se cultivation of eight dung samples from each herbivore, collected fo rtnightly between February and August. The four herbivores disperse ma ny seeds (spring averages are 6-15 seeds per gram of dry dung and maxi ma of 25-70) from a large number of species (totals between 52 and 78) . Dispersal seems to be mainly determined by seed production of the pl ant community. This is reflected in (i) the dissemination of a high pe rcentage of the species present in the dehesa, (ii) great seasonal var iability, related to seed production, in the amount of seeds and numbe r of species dispersed, and (iii) a high semi-quantitative similarity of seed content in the four types of herbivore dung throughout the yea r. There is also important quantitative variation that depends on anim al traits and feeding habits. These results and the characteristics of species found in dung suggest the adaptation of plant species to the dispersal of their seeds via herbivore gut. This process may well have profound implications for vegetation dynamics and the evolution of pl ant traits.