Diel activity patterns and overlap between Eurasian red squirrels and Siberian chipmunks in native and introduced ranges

Differential temporal behaviour promotes the coexistence of similar species, thus reducing interspecific competition. We investigated the overlap of activity patterns of invasive Siberian chipmunks <i>Eutamias sibiricus</i> and native Eurasian red squirrels <i>Sciurus vulgaris</i> in northeastern Italy; then, we compared our data with the activity of the same squirrel species in Mongolia, where both of them are native. Siberian chipmunks and Eurasian red squirrels resulted to be strictly diurnal species throughout their range. Both in the native and in the introduced range, the temporal activity of the Siberian chipmunk moderately overlapped with that of the larger Eurasian red squirrel, thus suggesting a limited temporal partitioning among these rodents. Levels of temporal overlap did not significantly differ between the native and the introduced range of the Siberian chipmunk. Our results provide further evidence that direct competitions may not occur between native Eurasian red squirrels and invasive Siberian chipmunks in Europe. This may be reflected by the different peaks of activity we found in spite of the general overlap in diel activity pattern, and/or by other unmeasured processes such as segregation in a spatial occurrence at the fine scale.

时间行为分化可促进近缘物种共存，进而降低种间竞争压力。本研究针对意大利东北部的入侵物种西伯利亚花栗鼠（*Eutamias sibiricus*）与本土物种欧亚红松鼠（*Sciurus vulgaris*）的活动模式重叠程度展开调查，并将所得数据与该两种松鼠在蒙古的活动数据进行对比——蒙古为二者的原生分布区域。研究结果显示，西伯利亚花栗鼠与欧亚红松鼠在其所有分布范围内均为严格的昼行性物种。无论是在原生分布区还是入侵分布区，西伯利亚花栗鼠的时间活动模式均与体型更大的欧亚红松鼠存在中等程度的重叠，这表明二者在啮齿类类群间仅存在有限的时间生态位分化。西伯利亚花栗鼠在原生分布区与入侵分布区的时间活动重叠度并无显著差异。本研究结果进一步佐证，在欧洲地区，本土欧亚红松鼠与入侵的西伯利亚花栗鼠之间可能不存在直接竞争。尽管二者的昼夜活动模式整体存在重叠，但本研究观测到二者的活动峰值存在差异，同时可能存在其他未被量化的过程（如精细尺度下的空间分布隔离），这或可解释上述研究结果。