PS 19-258 - Field mouse preference for dwarf bamboo and tree seeds: Long-period synchronized seeding and mortality of Sasa borealis may alter forest regeneration

Abstract: The Bambusoideae are a taxon of large-scale flowering seeding, and death plants with a long life cycle. Forest ecosystems are affected in various ways by these events; for example, a large supply of dwarf bamboo seeds increases the abundance of field mice, and mass defoliation improves the light conditions at the forest floor, likely promoting the germination of numerous plants. Field mice are seed predators and dispersers and thus strongly affect the survival and migration of the next generation of plants producing the seeds on which they feed. However, it is not entirely clear how field mice utilize dwarf bamboo seeds and whether they prefer these over tree seeds. Such information is important with regard to the fate of tree seeds, which coexist with dwarf bamboo seeds. Hence, the respective responses to dwarf bamboo seed should be examined using a comprehensive approach that includes tree seeds. Our objective was to clarify whether field mice exhibited different preferences for dwarf bamboo and tree seeds.
We examined two choices: one dwarf bamboo species (Sasa borealis) and one of four tree species with different acorn/fruit traits (Castanea crenata, Quercus crispula, Fugus crenata, and Lindera triloba). The seeds were placed in a container located in a forest where dead S. borealis culms remained, and they were monitored using an automatic camera. The species of visiting animals and the order in which they foraged on the examined seeds were confirmed using video recordings. The seed foraging rate was calculated by dividing the amount of the reduced seeds by the amount of the examined seeds. Seed preference was evaluated based on the respective rate and order.
The examined seeds were mainly foraged by two field mouse species, Apodemus speciosus and Apodemus argenteus. Their preference exhibited the order C. crenata, L. triloba, S. borealis, F. crenata, and Q. crispula. This suggested that the predation pressure on F. crenata and Q. crispula seeds can be considerably reduced in years of S. borealis mast seeding, if these trees coexist with S. borealis.
In conclusion, we found that mast seeding, a very rare phenomenon, can disrupt the normal pattern of survival (and even dispersal) of tree seeds, and may change the vegetation composition of forests in the future. We propose that the possibility of this vegetation change can be examined by verifying it together with the promoting effect of improved light conditions on germination after the death of S. borealis.