Mast seeding and predator-mediated indirect interactions in a forest community: evidence from post-dispersal fate of Rodent-generated caches.

Abstract

Abstract The impact of temporal variations in seed supply on rates of seed removal by rodents (Apodemus speciosus and Eothenomys andersoni) was examined to demonstrate that seed predation on Aesculus turbinata can depend on the seed abundance of other dominant tree species. The impact of seasonal variation in Fagus crenata seed fall was examined, in particular. Research was undertaken in two sites within the Kanumazawa Riparian Research Forest in Japan. Seed production of the three tree species (A. turbinata, F. crenata and Quercus mongolica) was recorded annually from 1992 to 1998 in the long-term monitoring plot. In each of the 3 years (1995-97), the fate of approximately 100 seeds of A. turbinata were monitored under each of the five mature trees in the short-term plot. The seed success of A. turbinata varied greatly among the 7 years of the study. Both A. turbinata seed survival and seedling emergence were particularly low during the F. crenata mast year and among the lowest in the 7-year observation period. No such trend was observed when Q. mongolica massively fruited. Only in 1996 were more seeds initially destroyed (60%) than cached. Seed predation was the predominantly source of seed mortality, accounting for between 93 and 100% of seed death. Although the fate of all seeds was not known, the proportion of seeds that germinated was low, ranging from only 1 to 3% with over 80% of seeds suffering predation in most years. In 1995, the rate of A. turbinata seed removal suddenly decreased in October despite an abundance of seeds. Rodents exhibited a strong, consistent preference to F, crenata seeds over A. turbinata and this preference increased as F. crenata seed became more abundant. results indicate that there was no clear relationship between rodent abundance and any of the seed fall measures, although their populations increased rapidly in the summer following F. crenata masting.