Noriko Tamura, Mutsumi Ito, and Fumio Hayashi (2021) Different Responses of Endemic and Alien Tree Squirrels to Tree Seed Chemicals. Mammal Study 46 (3): 237-250.

　This study used feeding experiments to evaluate differences in the tolerance of Japanese squirrels (Sciurus lis) and two alien tree squirrels, the Eurasian red squirrel (S. vulgaris) and Pallas’s squirrel (Callosciurus erythraeus), to tannins, a defensive chemical found in Quercus acorns, and terpenes in coniferous cones. The experiments revealed that both alien species had higher tolerances for tannins and could utilize most Quercus acorns. In comparison, the Japanese squirrel was less tolerant of tannins, but could consume a diet with high concentrations of terpenes, suggesting that it had adapted to the coniferous forest environment that has persisted since the Pleistocene. The feeding experiments in this study were well designed, controlling not only the concentrations of the defense chemicals but also the lipid contents, which could affect food consumption, and the experiments were repeated appropriately. This study provides an excellent model for future similar experiments in this field. This study should be regarded as significant, since it made a novel finding of how an endemic species has adapted to a unique environment, and could explain the expansion of alien species in the light of the chemical properties of their diets. This study is likely to have high social value because it shows the need to maintain a favorable environment to conserve endemic species and to construct guidelines for dealing with alien species based on valid scientific evidence.