Effects of hoarding activity of Apodemus mice on the regeneration and spreading of acorn-producing tree species.

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To clarify the effects of the hoarding activity of Apodemus mice on the regeneration and spreading of acorn-producing tree species, I studied the population dynamics and hoarding behavior of Apodemus mice, the acorn production of Pasania edulis, and its mortalities from acorn-production to seedling-establishment. A.speciosus and A.argenteus showed the same seasonal changes in their numbers every year ; the population was largest in spring, decreased during summer and fall, and then increased from late fall. The annual changes in the number of resident mice during winter and the acorn production of P.edulis did not always correspond. The masting of P.edulis acorns was recorded every 3-4 years, and in the mast years, the percentage of empty acorns was low. Apodemus mice transported dropped acorns 10-50m, on average, and hoarded them in the soil. The percentage of the transported acorns varied with the intensity of predation by middle- and large-sized mammals such as wild bores. About 60% of cached acorns were recovered by their hoarders and about 40% of them were stolen by mice other than the hoarders. In both cases, the recovered acorns were transported farther from their mother trees. I made the life tables of the acorns produced from 1995 to 2008, and conducted a key-factor analysis. The annual changes in the total mortality of acorns during the period from acorn-production on the trees to seedling-establishment (Total K) was determined by the intensity of the predation of dropped acorn by Apodemus mice (k21). The density relationships of Total K and k21 were inversely-density dependent. Out of the 14 years, Apodemus mice could act as seed-dispersers and contribute to the regeneration and spreading of acorn-producing tree species only in three mast years with a low mice population ; 1999, 2003, and 2007, and in the other 11 years, mice seemed to act as seed-predators.