Japan’s Ryukyu Islands, which include Okinawa, are home to two rare mammals, the Amami rabbit and the Ryukyu long-haired rat. These animals are difficult to observe, but conservationists want to understand specific details of their diets.
So researchers, including from the University of Tokyo, examined the teeth of deceased animals to see what the animals ate. Their results showed that the rabbits had a consistent diet, while the rats’ diet varied with the seasons. The study was published in the journal Mammal Research.
When you think of Japan’s islands, such as Okinawa, located in the Ryukyu Islands in southwestern Japan, you probably think of sun and surf, but hidden deep in the shady forests of these islands are many small mammals that have lived there for thousands of years.
Some species, like the Amami rabbit, are considered “living fossils” because their most recent mainland ancestors have long since gone extinct. Both the Amami rabbit and another local resident, the Ryukyu long-haired rat, are extremely rare. Efforts to protect these species are underway given the growing complexity and severity of climate change issues, as well as other human impacts that the region may be experiencing.
“Climate change and human activities can have adverse effects on the environments in which animals live. This can have adverse effects on their feeding patterns and food sources,” said Mugino Kubo, associate professor in the Department of Natural Environmental Studies.
“Therefore, to better understand the lives of these rare animals, our goal is to clarify the feeding habits of these species and gain insight into their ecological context to inform conservation strategies. Our latest research explores the diets of the Amami rabbit and the Ryukyu long-haired mouse, particularly their seasonal variations.”
Kubo and her team analyzed microscopic wear patterns, or microwear, on the tooth surfaces of the two species, using 3D texture analysis to determine what they eat year-round.
The teeth were taken from wild samples killed on the road, and the team compared them with teeth from laboratory-reared rodents with known feeding histories. This comparison can reveal what wild populations eat without the huge effort of monitoring them, which is essentially impossible.
“Our results show that Amami rabbits eat tough plants such as ferns year-round due to constant microwear, while Ryukyu long-haired rats change their diet with the seasons, eating soft foods such as fruits, slugs and eggs in the summer and hard foods such as seeds and acorns in the winter, depending on the different microwear,” Kubo said.
“This study shows that tooth microwear texture analysis can reveal the feeding habits of rare species that are difficult to directly observe in the wild. In addition, our results suggest that seasonal dietary differences should be more carefully considered in ecosystem management.”
The research team plans to conduct further studies to compare populations of the same species on different islands in the Ryukyu Archipelago. They also intend to use DNA analysis and other methods to gain a deeper understanding of the species’ dietary habits.
“While this study did not directly explore the impact of human activities, previous studies have shown that the unique ecosystems of the Ryukyu Islands are threatened by human activities, leading to their decline,” Kubo said. “Future comparisons with older specimens in museums may reveal dietary or ecological changes caused by recent human activities.”
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