Indirect negative influence of dwarf bamboo on survival of Quercus acorn by hoarding behavior of wood mice.

摘要

To clarify the influence of dwarf bamboo (Sasa spp.) on patterns of seed dispersal by wood mice, the destinations of 480 magnet-inserted acorns (Quercus mongolica var. grosseserrata) were tracked with a magnetic locator from autumn to the following spring at two adjoining sites in a broad-leaved deciduous forest, a Sasa-removed site and a Sasa-growing site. The disappearance speed of acorns placed at the Sasa-growing site was higher than at the Sasa-removed site. Of the 480 acorns, 285 (59.4%) were located in the spring. At the Sasa-removed site, acorns that were placed at 5 m and 15 m from the border of Sasa coverage tended to be transported to the adjoining Sasa-growing site. Meanwhile, the acorns placed at the Sasa-growing site tended to remain there. The details of transported site and the depth frequency distribution of acorns differed between the sites. The percent of surviving acorns found at the Sasa-growing site (1.1%) was significantly lower than that of acorns found at the Sasa-removed site (15.9%). These different patterns of seed dispersal by wood mice seemed to be caused by the strong habitat preference of wood mice for a site with rich forest floor vegetation. These results suggest that dense Sasa coverage not only directly inhibits regeneration of Quercus trees by shading their seedlings, but also indirectly inhibits their regeneration by providing a suitable habitat for wood mice and thereby causing high predation pressure for acorns at post-dispersal. Furthermore, this predation pressure of mice on acorns may operate even 15 m outside the Sasa coverage, showing rather negative consequences for directed dispersal.