a1 Instituto de Ecología, Universidad Nacional Autónoma de México. Apartado Postal 70-275, C.P. 04510, Ciudad Universitaria, México DF, México
a2 Instituto de Biología, Universidad Nacional Autónoma de México. Apartado Postal 70-367, C.P. 04510, Ciudad Universitaria, México DF, México
a3 Centro de Investigaciones en Ecosistemas, Universidad Nacional Autónoma de México. Antigua Carretera a Pátzcuaro no. 8701, Ex-Hacienda de San José de la Huerta, C.P. 59180, Morelia, Michoacán, México
This study tested whether the reduction in the number of large-bodied seed dispersers is correlated with shifts in the taxonomic and functional (e.g. dispersal mode and seed size) traits of the seeding communities within small fragments of semi-deciduous forest, southern Mexico. In five fragments (2.3–640 ha) and one continuous forest site we sampled tree and seedling species in 40 (20 × 20 m) and 120 (3 × 3 m) plots respectively, and recorded the incidence (presence/absence) of the disperser fauna (three common large-birds and >500-g mammals). Tree and seedling species were categorized according to dispersal mode, seed size and whether they originated from local (i.e. from dropped) or immigrant (i.e. from actively dispersed) seeds. Fragment size negatively correlated with number of species of medium to large vertebrate seed-dispersers and number of seedlings of large-seeded species, but had no influence on functional traits of the adult-tree community. Between 41% and 61% of all seedlings were considered as immigrants and the proportion of immigrant seedlings of large-seeded tree species was negatively correlated with forest size. The results suggest that biased defaunation in small forest fragments may seriously reduce recruitment of large-seeded tree species (>1.4 cm length) dispersed by vertebrates, negatively affecting successional trajectories of small forest fragments.
(Accepted September 19 2009)