Postdispersal Seed Predation on Sisyrinchium arenarium (Iridaceae) at Two Elevations in the Central Chilean Andes

Abstract

Postdispersal seed predation in alpine communities has received surprisingly little attention. We evaluate the magnitude of seed predation by ants and avian granivores in the perennial herb Sisyrinchium arenarium through a field experiment at two different elevations (2700 and 2000 m) in the central Chilean Andes. A total of 96 pots, containing 50 seeds each, were placed at each elevation and randomly assigned to one of four treatments: control, bird exclusion, ant exclusion, and total exclusion (wind control). We also compare the activity of ants and avian granivores at the two elevations. Mean percentage seed removal by wind was 23 and 21% at 2700 and 2000 m elevation, respectively. Overall, after subtracting seed loss by wind, seed removal by granivores was low at both sites (2–14%), although it was significantly greater at the higher elevation (2700 m). This was concordant with the greater activity of ants and granivorous birds there. Seed removal by ants was greater than by birds at the higher site (14 vs. 4%, respectively), but did not differ at the lower elevation (3 vs. 2%, respectively). Results contrast with those reported for central Chilean mediterranean-type climate shrublands at lower elevations where avian and rodent granivory is important, while that by ants is low. Future studies considering plant species with different seed characteristics (e.g., size, shape, energetic value) and taxonomic affiliation will be necessary to assess the general importance of this ecological process in the central Chilean Andes and alpine areas in general.