The separation of ecological niches in terms of food resource, activity pattern or space contributes to the coexistence of sympatric species. Spatiotemporal variations in resource availability affect foraging behavior, habitat selection and even the existence of species. To explore the coexistence mechanisms of sympatric rodents, variations in food habit, viscera organ and digestive tract morphology among different rodent species were investigated in Shennongjia, central China.
Studied rodents were trapped by snap-trap in October 2010. Upon capture, all rodents were carried to laboratory. The species, gender, age, reproductive status, body mass and length were recorded. Then the heart, lung, liver, spleen, kidney and the entire digestive tract were removed from the body and the carcass mass was weighted. The connective tissue and lipid was stripped and the digestive tract was extended to its full length. Fresh weights of all organs and lengths of digestive tract were weighted. After removing digestive tract contents, fresh weights without contents and food items in the stomach were recorded. Dry weights of all organs were measured after drying in the oven.
A total of 220 adult rodents, including 8 Niviventer andersonii, 167 N. confucianus, 5 Apodemus chevrieri, and 35 A. draco, 2 Leopoldamys edwardsi and 3 Typhlomys cinereus, were collected for analysis. L. edwardsi and T. cinereus were excluded for statistical tests due to insufficient samples. The analysis of food habit showed that N. andersoni, N. confucianus, A. chevrieri and A. draco were omnivorous but the Chi-square test detected significant variation in dietary biases. N. andersoni was primarily phyllophagous and seminivorous and the others were primarily seminivorous and carnivorous. The analysis of covariance of viscera organs showed that while fresh weights of heart, lung and spleen and dry weight of spleen did not differ between rodents, other indices did exhibit significant variation with the highest value found in N. andersoni. In the analysis of digestive tract morphology, while length, fresh and dry weight of caecum did not differ between rodents, fresh and dry weights of stomach and large intestine, fresh weights including stomach, caecum and large intestine contents, and length of large intestine did differ significantly with the highest value found in N. andersoni. Otherwise, the length, fresh and dry weight of small intestine, and fresh weight including small intestine contents also showed significant variations between species, with the highest value found in N. confucianus.
Variations in viscera organ morphology of N. andersoni compared to other species indicate that the segregation of food resources contributes to this species coexistence with other rodents. In order to adapt to different availability of food resources, the viscera organ and digestive tract morphology of N. andersoni show adaptable phenotypic plasticity. However, A. chevrieri and A. draco, both belonging to the genus Apodemus, do not exhibit differences in food habit, viscera organ and digestive tract morphology, which implied that their coexistence may result from other strategies than resource allocation, such as habitat selection.