Certain plants produce large seed crops, often in the form of masting, which in turn leads to an increase in the population of the animals that utilize them (Ogawa et al., 2017). These seed-utilizing animals are known to both predate and cache seeds for later use. Such interactions between seed predators and seeding plants have been widely studied in trees with masting seeds, such as acorns, at intervals of several years (Jensen and Nielsen, 1986; den Ouden et al., 2005; Saitoh et al., 2007). However, for plants that require decades or even centuries to produce seeds, such research has inevitably stalled. Moreover, the fauna that utilizes the seeds of such plants also remains largely unknown. For example, the mast seeding of Bambusoideae is associated with increased populations of several rodent species (Gonzalez et al., 2000; Bovendorp et al., 2020; Suzuki et al., 2022), but the causal relationship between them is speculative. Thus, the interaction between the rodents and the seeds (Klinger and Rejmánek, 2009), and whether Bambusoideae show a functional response to the rodents remain unknown. If the rodents act as both seed predators and seed dispersers, they may have a positive impact on the Bambusoideae. In contrast, the expansion of certain bamboo species such as the dwarf bamboo, Sasa borealis, seed dispersal could threaten other plants, since its leaves cover the forest floor and prevent the regeneration of other species (Nakashizuka, 1987), resulting in changes to the original vegetation and ecosystems over time. To elucidate these issues, we conducted a feeding test on S. borealis seeds, after the seeding event that occurred in plants that have been established in the site for 120 years. During the test period, the behaviors of animals that interacted with the seeds were recorded using trail cameras to observe how they handled the seeds, and to look out for novel behaviors such as seed removal and small-seed caching (Vander Wall, 2003). The forest floor conditions, and season are related factors that are known to alter seed foraging behavior in mice (Kikuzawa, 1988; Haugaasen et al., 2010; Best et al., 2022). By conducting the study in areas with different forest floor conditions and in different seasons, we aimed to determine whether this pattern of plant–animal interactions occurs with small seeds such as S. borealis. The findings from this experiment on the use patterns of S. borealis seeds by animals can provide a first step towards understanding the ecological role of Bambusoideae seeds supplied through interval masting over longer timescales.

This study revealed that the only animals that utilized S. borealis seeds, which were supplied in large quantities at the same time as a masting phenomenon, in central Japan were two species of Japanese mice. A study based in Chiloé, Chile, revealed that Bambusoideae seeds were consumed by rodents as well as birds (finch-like species and the large pigeon) (Willson and Armesto, 1996). Yet, we did not observe any squirrels and granivorous birds utilizing the seeds in our study. However, N. procyonoides was observed approaching and the possibility of foraging cannot be ruled out.

The seed utilization rate was found to change with season and the interaction between season and plot. Forget (1992) and Shimada (2001) showed experimentally that the behavior of rodents, whether or not they forage for the seeds, depends on the presence other foods at the same time. Therefore, the lack of other seeds to forage in summer may be the reason for the high utilization rate of S. borealis in both our plots. In fall, other seeds such as acorns of Q. crispula were potentially supplied inside and outside Plot-BF, resulting in the low utilization rate of S. borealis. Meanwhile, in Plot-CF, a coniferous forest, there was no such supply, and the high rate may be unchanged from summer.

Camera capture using trail cameras confirmed that mice not only predated and/or removed seeds with a high frequency but also often buried or cached them in the ground, thus providing novel evidence for small seeds being targeted for caching. Previous studies such as Vander Wall (2003) used trials on rodents as large as A. speciosus and revealed that small seeds (mean 8.7 mg) were predated upon but large seeds (>55 mg) were cached. Similarly, Wang et al. (2012) also reported that experiments conducted on the habitat of Apodemus sp. showed that larger seeds (mean 335 mg) were cached but smaller seeds (<28 mg) of several species were only predated upon. Thus, our study provides new insights that contradict the patterns of predation and caching observed in these previous studies and show that mice can cache small seeds and may have a role as a disperser of small S. borealis seeds.

Regarding seed handling patterns, A. specisus tended to have a higher percentage of predation at IN and removal at OUT. This is in accordance with general rodent behavior, which is the need to avoid natural enemies during feeding, and thus, their predation rate increases in safe places with adequate cover (Phelan and Baker, 1992; Kollmann and Buschor, 2003). The dead S. borealis culm cover in the IN group can function to reduce the predation risk on rodents compared with OUT. Furthermore, the seed predation time of the mouse was longer in IN than in OUT, suggesting that A. speciosus were eating the seeds without fear of predators in IN. In contrast, A. argenteus showed no clear trends in the results. The main reason for the lack of distinct trends may be because A. argenteus is smaller than A. speciosus in body size (Oka, 1992), and therefore cannot act freely to avoid A. speciosus in the coexisting habitat. In addition, based on the number of recordings, A. argenteus barely visited the Plot-BF in Summer-II, and yet this site was concurrently used freely by A. speciosus, suggesting the existence of interspecific competition between the two species. Moreover, the large difference in habitat use by both species in fall may be explained by their differential preference for Q. crispula acorns. Acorns are too large in size to be taken away by A. argenteus, and contain tannins, which act as a protective substance in A. argenteus but not in A. speciosus (Shimada et al., 2004; Saitoh et al., 2007). Therefore, A. speciosus appeared to change its primary food from S. borealis seeds to the available Q. crispula acorns, whereas A. argenteus maintained its prioritization of S. borealis seeds.

In conclusion, this study revealed that the small S. borealis seeds were consumed by mice and were a target for caching, and that the utilization pattern varied according to mouse species, location, and season. In relationships between plants, particularly acorns, and their animal predators, the animal plays an important role in seed dispersal (Klinger and Rejmánek, 2009). This contributes to forest regeneration, which is an important focus area in ecology and evolution. Our study reports on a novel research concept that integrates a very long-period masting event in dwarf bamboo, which produces very small seeds, with the plant’s relationships with other species. Therefore, further research is required to clarify how seeds produced by masting in species such as S. borealis may affect forest ecosystems, while considering other plant taxa in the ecosystem. In this context, future research should examine animal seed preferences among S. borealis and other plant taxa.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: https://figshare.com/s/7ac7a1e2bf34a12aeabd.

Ethical review and approval was not required for the animal study because the study is a contactless observation of the behavior of wild animals in the field.

HS and HK conceived the ideas and designed the study. HS collected field data, analyzed the data, and wrote the first draft of the manuscript. HK substantially contributed to revising the manuscript and supervised the study. All authors contributed to the article and approved the submitted version.