Effects of asynchronous acorn production by co-occurring <i>Quercus</i> trees on resource utilization by acorn-feeding insects

Abstract

To clarify the effects of asynchronous seed production among tree species on the population of seed predators, we investigated the relationship between the annual variation in production of mature acorns and the insect damage in those acorns of two sympatric oak species, Quercus variabilis Blume and Quercus serrata Thunb. ex Murray, over 4 years at two study sites. The annual variation in acorn production was noticeable, with a coefficient of variation (CV) at the two sites of 1.05 and 0.80 for Q. variabilis and 0.87 and 0.73 for Q. serrata. Annual fluctuation in acorn production by Q. serrata was synchronized between the two sites. Since annual fluctuation in acorn production was not synchronized between the two species, the CVs for the total acorn production by both oak species (0.83 and 0.62 at the two sites) were lower than those for Q. variabilis and Q. serrata alone. The rate of predation by the specialist predators (Curculio weevils) on the acorns of both species was not related to the annual acorn crop size. Prolonged diapause of Curculio weevils might stabilize their populations. The rate of acorn predation by the generalist predators (tortricid moths) was also not related to the annual crop size. Asynchronous acorn production by the two oak species would help to stabilize the population.