Noble savages: human-independent Rattus rats in Japan

ABSTRACT

Brown (Rattus norvegicus) and black (R. rattus sensu lato) rats are among the world’s most widespread and important invasive animals; however, there are very few studies of their natural history in natural habitats within their native ranges. Both taxa are native to Japan and still occur in natural habitats there, but have been traditionally treated by zoologists working in the country as invasive pests limited to cities and agricultural lands. We used thermal imaging and snow tracking to conduct the first study of status, distribution and behavioural ecology of remnant human-independent populations of these species in Japan. We found both species still living in natural habitats away from human settlements: brown rat is a rare species in wetlands on the main islands and in upland forests on Hokkaido, while the native taxon of R. rattus species complex, the Asian house rat (R. tanezumi sensu stricto) inhabits remnant deciduous old-growth forests, as well as evergreen subtropical forests, in the south of the country. Such knowledge is critically important for understanding the rats’ evolutionary history, invasion biology and behaviour. Future molecular studies should aim to clarify the origin of these populations: possibly they are Pleistocene relicts threatened by hybridisation with rats of related non-native taxa.

KEYWORDS:

• black rat
• brown rat
• habitat
• invasive species
• Oriental field rat
• origin

Acknowledgements

We thank Alexei Abramov, Wenbo Chen, Hiroshi Dewa, Evan Economo, Nicholas R. Friedman, Anna Gritsuk, Noritaka Ichida, Anastasia Kadetova, Lyudmila Khlyap, Mikhail Kosoy, Yoshimura Masashi, Shawn Miller, Jason Munshi-South, Masako Ogasawara, Yuka Ozaki, Jason Preble, Vladimir Shkurov, and numerous residents of the Japanese Islands for help with various aspects of field research, data gathering and manuscript preparation.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research was funded by subsidy funds from Okinawa Institute of Science and Technology and conducted under OIST permits FWP-2017-034 and FWP-2018-024.