PARENT SESSION
Poster Session # 9: Herbivory.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Facilitation vs. apparent competition and the establishment of tree seedlings beneath nurse shrubs in northern Patagonian.
Mazia, Noemi1, Chaneton, Enrique*,1, Kitzberger, Thomas2, 1 Facultad de Agronomía, Universidad de Buenos Aires, Buenos Aires, Buenos Aires, Argentina2 Universidad Nacional del Comahue, Bariloche, Rio Negro, Argentina
ABSTRACT- Facilitative interactions play a major role in plant recruitment in stressful environments. Yet, negative indirect effects mediated by herbivorous consumers can potentially mask the effects of facilitation between neighbouring plants. Our objective was to evaluate how seedling predation by tenebrionid beetles affects the likelihood of tree establishment in a xeric forest-steppe ecotone in northern Patagonia, Argentina. We hypothesized that apparent competition arising from incidental predation of newly emerged seedlings by omnivorous beetles would decrease Austrocedrus chilensis recruitment under "nurse" shrubs, a process otherwise facilitated by shrub-canopy shading. Seedlings of A. chilensis were transplanted into each of three microsites (beneath shrub, off-shrub sheltered and off-shrub open), both within enclosures having natural or elevated beetle densities and in unenclosed areas. Desiccation was the main source of seedling mortality (90%) in open microsites. Beetle addition increased seedling predation from 15 to 60% beneath shrubs, and from 3 to 20% in off-shrub sheltered microsites. Pitfall trapping confirmed that beetles numerically aggregated in shrub patches, while litter removal/addition indicated that shrubs provided both food and microhabitat to tenebrionids. Laboratory trials showed that tree seedlings were most vulnerable to beetle attack within one month from emergence. Thus, early seedling mortality due to beetle predation reduced the strength of, but did not completely eliminate, tree facilitation by shrubs. Our results suggest that the balance between facilitation and apparent competition may influence the long-term structure of this ecotonal plant community.
Key words: herbivory, Patagonia, indirect interactions, plant recruitment