Effects of habitat fragmentation on frugivorous birds and on seed removal from Pistacia lentiscus in two contrasting fruiting seasons

Abstract

Successful animal seed dispersal is the result of the interaction between frugivore behavior and the distribution of food resources, which can vary over space and time. We evaluated the interaction between avian frugivores and the masting shrub Pistacia lentiscus in both connected and isolated forest fragments along the Guadalquivir valley (south Iberian Peninsula) in two contrasting fruiting seasons (mast and non-mast). We compared the abundance and composition of avian dispersers and seed predators, recorded fruit removal rates by dispersers and predators, and investigated potential changes in the arrival of seeds to forest fragments. Our results showed that there was a greater abundance of dispersers in connected than in isolated fragments in the mast season (i.e. high fruit availability) but the opposite pattern in the non-mast season (i.e. low fruit availability). The effects of habitat fragmentation were more noticeable on medium-sized than small bird dispersers. Medium-sized birds were more abundant in isolated forest fragments but their abundance was highly dependent on the season, while small bird dispersers were apparently unaffected by fragmentation. Seed removal rates were higher in isolated than in connected fragments in the mast season but not in the non-mast season; predation rates were negligible in both seasons. Seed arrival was consistent between seasons and microhabitat where the dispersed seeds were deposited, most seeds being dispersed under the canopy of female Pistacia plants. We highlight the influence of the interplay between seasonality and landscape configuration on patterns of frugivore-mediated seed dispersal. Thus, despite its direct link to plant–frugivore interaction, the effects of habitat fragmentation on frugivores and plants were decoupled in our study system. These decoupled responses seemed to be chiefly due to the high feeding dependence of dispersers on P. lentiscus fruits.