唐家河自然保护区高山姬鼠和中华姬鼠夏季生境选择的比较

为揭示影响高山姬鼠和中华姬鼠夏季空间分布的生态因素,采用样线法和样方取样法,于2009年6—8月在四川省唐家河国家级自然保护区内对两种姬鼠的生境选择进行了比较研究。结果表明:两种姬鼠主要利用坡度平缓,郁闭度、落叶层盖度、乔木胸径和高度较小,灌木、竹子和草本密度适中而草本盖度较大的生境;高山姬鼠频繁出现在海拔较低(1400 m左右)、草本植物较大(平均高度为16—30 cm)的生境中,而中华姬鼠频繁出现在海拔较高(1900 m左右)、草本植物较小(平均高度<15 cm)的生境中。此外,高山姬鼠频繁出现在竹林较矮(平均高度<1 m)、水源距离较近(<50 m)、植被演替阶段较低(小树林)的常绿-落叶阔叶混交林中,而中华姬鼠对这4种生态因子无明显的选择性。两种姬鼠在对生境的利用上虽具一定重叠性,但对诸多生境变量选择上的差异表明各自具有不同的生境利用模式。海拔、植被演替阶段、郁闭度和草本高度4个生境变量判别函数系数的绝对值明显大于其他变量,表明高山姬鼠和中华姬鼠在生境上的分割可能主要与这4个变量有关。生境利用模式的不同有助于两种姬鼠同域共存。

A comparison of summer habitats selected by sympatric Apodemus chevrieri and Apodemus draco in Tiangjiahe Nature Reserve, China

Habitat selection among allied species is one of the key supports for niche theory in ecology. Line transects and systematic sampling was used to study habitat selection by Chevrier's field mouse and the South China field mouse from June to August 2009. The two species are sympatric in the Tangjiahe Nature Reserve, Qingchuan County, Sichuan Province, China. We compared habitat plots used by both mammals and control plots reflecting the environment at large to investigate their habitat use patterns. 140 plots were measured totally. Of which, 49 were used by Chevrier's field mouse, 41 were used by South China field mouse and the rest 50 were control plots. 21 environmental variables potentially influencing their habitat selection were measured. In univariate analysis, 16 variables were significantly different between plot groups, indicating the two mammals both have a distinct significant habitat preference. In addition, their selected habitats overlapped to some extent: they both preferred for habitats with gentle slopes, lower canopy height, significant fallen leaf ground coverage, a relatively higher proportion of open land, larger tree diameter at breast height, greater tree height, moderate shrub bamboo and herb density, and larger herb coverage when compared with the control plots. Significant differences in habitats selected indicated the two species have distinct habitat selection patterns. Chevrier's field mouse occurred more frequently in habitats with lower elevations (about 1400 m) and taller herbs (about 16-30 cm), while South China field mouse occurred in habitats with higher elevations (about 1900 m) and shorter herbs (<15 cm). Moreover, Chevrier's field mouse preferred for habitats characteristic of evergreen and deciduous mixed broad-leaved forests, a shorter distance to water sources (<50 m), vegetation in earlier successional stage (a small growth of trees) and shorter bamboo height(<1 m). South China field proved to be more of a generalist with no prominent selectivity for the above ecological factors. This indicated the former's habitat is more decentralized while Chevrier's field mouse's habitat is more centralized or its habitat use is more specialized. Stepwise discriminant function analysis showed the four variables of elevation, vegetation stage of succession, canopy, and herb height contributed more to habitat separation between the two small mammals than others. The higher discriminant function coefficients indicated the two species could coexist sympatrically. Habitat-use strategies are often cited as the means by which sympatric species avoid competition. Occupying separate microhabitats is common among sympatric species. It seemed that these two small mammals can coexist and evolve in the same region contributing to their temporal and spatial separation in habitat use. Since they have similar body sizes and breeding dates and share the same food sources, we hypothesize habitat separation between the two species may not have resulted from differences in physiological and ecological requirements, but from ecological or evolutionary adjustment to reduce interspecific competition.Based on our findings, different habitat management strategies should be adopted for the two species.