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The Fascinating Relationship Between Mice and a Plant Species That Blooms Once Every Century
Researchers have discovered several factors that influence the behavior of field mice, using seeds from dwarf bamboo plants, a species that blooms only once every hundred years. Their findings not only point to the previously undervalued role of mice in the forest ecosystem but also show that they store small sasa seeds for later use. This challenges a previously held model of mouse behavior.
Research on Mouse Behavior
Researchers at Nagoya University in Japan have gained new insights into the interaction between mast-seeding plants and the animals that consume their seeds. Hanami Suzuki and Professor Hisashi Kajimura studied the behavior of field mice using seeds from the once-in-a-century-blooming sasa bamboo plants in central Japan.
They discovered that the seed usage patterns of field mice varied by species (large Japanese field mouse, Apodemus speciosus, and small Japanese field mouse, A. argenteus), the presence or absence of understory vegetation, tree species (broadleaf forest or coniferous forest), and season (summer or fall). These findings underscore the importance of understanding the needs of both plants and animals to ensure the health of local ecosystems. They also undermine a previously held belief about how mice store seeds.
Mast-Seeding and Mouse Foraging Behavior
Dwarf bamboo (Sasa borealis) exhibits mast-seeding behavior over wide areas. This means that a plant collectively blooms and seeds at regular intervals to overwhelm predators and maximize pollination rates. However, mast-seeding events are rare, with intervals of up to 120 years. When they do occur, the resulting abundance of seeds in the forest provides easily available food for various animals, especially rodents like field mice.
To understand more about the behavior of field mice during mast-seeding events, the researchers placed seeds in shallow mesh baskets to simulate mass blooming and seed production. They then used an automatic camera to record the foraging behavior of field mice in different forest environments and in different seasons.
Initially, as expected, some mice ate seeds on the spot. However, others exhibited "dispersal behavior," carrying seeds away and burying them for later use. This is an example of a behavior known as "removal and caching."
Differences in Behavior Between Mouse Species
The two mouse species also behaved differently. The large Japanese field mouse consumed seeds in places where plants and bushes provided protection from predators. They also carried seeds away from areas where they were more vulnerable, such as open areas without vegetation. The small Japanese field mouse, on the other hand, was more likely to carry seeds to another location, even when protective vegetation was present. The researchers suspect that differences in body size probably explain this behavior. Larger mice are less concerned about other rodents stealing their food.
Seasonality and tree species also appeared to affect how frequently the mice ate the seeds. The rodents were more likely to consume seeds immediately in summer than in fall, probably due to the availability of food. They were also more likely to consume seeds on the spot in coniferous forests than in broadleaf forests, again probably because of the availability of other food stores. Since alternative food sources for later consumption, especially acorns, are more abundant in broadleaf forests, a mouse can afford to consume seeds right away.
The Role of Mice in the Ecosystem
Mice were also more likely to consume their food immediately in broadleaf forests during the fall. This behavior plays an important role in spreading seeds throughout the forest. According to Suzuki: "Forest-dwelling field mice play an important role in the distribution and renewal of trees because they act as seed dispersers that transport and store seeds. This suggests that we need to reconsider the relationship between the simultaneous seed production of S. borealis and field mice. It may also influence food selection with other tree seeds and the prediction of forest renewal and vegetation succession connected to it."
Suzuki explained that "the simultaneous seed production of sasa species is known worldwide to cause large outbreaks of field mice, which are typical seed-eaters. It has been studied as a prominent example of the effects of plants on animals. As seed predators, the choices and behaviors of mice, such as feeding or 'removal and caching,' can lead to inhibition of certain plants or enhance their ability to regenerate. When I learned about this, I became really interested in field mice as an important species for the future of forest ecosystems."
Conclusion
Many studies have been conducted on the relationship between field mice and seeds. The established theory states that larger seeds, such as chestnuts and acorns, are subject to removal and caching, while smaller seeds are consumed more quickly. However, our results revealed that even much smaller seeds, such as those of Sasa borealis, which weigh as little as about 0.025 g per seed, are also a target for mice. Therefore, the dispersal and storage behavior of field mice for seeds as small as sassafras suggests that the established theory needs to be revised.
Kajimura concludes: "Our experiments showed that field mice consider the surrounding environment and flexibly utilize Sasa seeds. Since this kind of behavior affects tree regeneration, as well as understory vegetation, our findings show the influence of mice on the complexity of the forest ecosystem."
Professor Hisashi Kajimura (he) and doctoral student Hanami Suzuki (she) are researchers at the Graduate School of Bioagricultural Sciences at Nagoya University, Japan. Their findings were published in the journal Frontiers in Ecology and Evolution.
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