Fruit resource tracking by avian seed dispersers in a temperate forest of southern South America: a matter of spatial scale

GARCÍA, D; AMICO, GC

Chico, California, EE.UU.

Congreso; Botany 2006; 2006

Fleshy fruits are sessile and spatially aggregated resources for frugivores. Fruit clumpiness is, however, scale-dependent and therefore the outcome of seed dispersal depends on the ability of frugivores to track for fruits at multiple spatial scales. In a temperate forest of southern South America (TFSA, NW Patagonia, Argentina), we quantified the abundances of ripe fruits in the understory (mostly from Aristotelia chilensis), the structure of the forest (tree cover, understory cover and height, woody plant volume, branches abundance), and the abundance of frugivorous birds (Elaenia albiceps and Turdus falklandii) along a 1,500 m transect. We evaluated the spatial patchiness of fruit and bird abundances by Moran’s I correlograms. We disentangled the spatial variability of bird abundance by using Principal Coordinates of Neighbor Matrices analysis (PCNM). We checked for the relationship among the abundance of birds predicted by PCNM at three spatial scales and fruit abundance, tree cover, understory cover and branch abundance, with multiple regression analyses. The abundance of fruits and birds showed significant, but different, spatial structures along the transect. Fruits patchiness was hierarchical, with small patches nested in larger patches. Birds abundance distributed mostly in single patches of intermediate size. The PCNM explained ca. 60% of the observed variability in bird abundance, mostly at large (36%) and intermediate (22%) scales. At the largest scale, bird abundance was positively and significantly related with forest cover, and only marginally with fruit and branch abundances. At the intermediate scale, birds abundance responded positively and significantly only to fruit abundance. The abundance of frugivorous birds acting as seed dispersers in the TFSA depends on different ecological factors at different spatial scales. Fruit resource tracking only operates at particular small extents within large landscape units.