北草蜥种群间生活史变异的成因分析:热环境、食物可利用性和体温的岛屿间差异

The causal analysis of inter-population variation in life histories of the northern grass lizard Takydromus septentrionalis: between-island differences in thermal environment, food availability and body temperature

比较浙江温州北麂岛与洞头岛的热环境、食物可利用性以及动物体温,以辨析北草蜥岛屿种群间生活史特征差异中环境因子的作用。通过测定岛屿上北草蜥栖息地植被和环境温度,比较岛屿热环境的差异。野外测定活动蜥蜴的体温、环境温度和活动规律,实验室温梯板中测定动物喜好体温。用陷阱法测定无脊椎动物多样性和丰度,以比较岛屿蜥蜴种群的食物可利用性。岛屿植被存在差异导致热环境的差异。洞头岛植被高于北麂岛,地表层光线透入率则低于北麂岛。因而,洞头岛郁闭地表的平均温度和最高温度显著低于北麂岛,但两岛裸露地面的温度无显著差异。热环境的岛屿间差异进而影响北草蜥的野外体温。在春季,洞头岛的野外有效温度和基底温度显著大于北麂岛,而两岛北草蜥的体温无显著差异;在夏季,洞头岛的北草蜥体温、有效温度和基质温度均显著高于北麂岛;到秋季,北麂岛蜥蜴体温和环境温度高于洞头岛。地面无脊椎动物多样性和丰度的岛屿间差异表明北麂岛食物可利用性大于洞头岛。岛屿间北草蜥日活动规律和喜好体温无显著差异。本研究表明:(1)温度和食物可利用性存在岛屿间差异,岛屿种群间生活史特征差异可能与之有关;(2)两岛屿北草蜥主要采取行为调节对策来适应自然界的热环境变化,尚未发现热生理学特征的进化性漂移[动物学报51(5):797-805,2005]。

In order to identify the environmental causes of inter-population variation in life histories of a Chinese lacertid lizard Takydromus septentrionalis, we determined the thermal environment, lizard body temperature and food availability on the Beiji and Dongtou islands in Zhejiang Province, of eastern China. We compared the thermal environments of the two islands by evaluating the vegetation in May, 2004 and recording the environmental temperatures in the habitat of the lizard from April to September, 2004. We also measured the field active body temperatures of the lizards and associated operative temperatures and substrate temperatures with a quick-reading thermometer in spring, summer and autumn respectively. Meanwhile, the activity patterns of lizards from the two islands were analyzed using the data from the investigation of field body temperature. We calculated the number of lizards captured per hour as the index of activity. In April, 2004, we captured 30 adult lizards from each island, and determined the preferred body temperatures of the lizards in a thermal gradient. The diversity and abundance of ground-dwelling invertebrates were used as the indicators of food avail- ability and were determined using traps in the two islands in May, 2004. The investigation of habitats indicated that the lizard＇ s habitats differed remarkably in vegetation and thus in thermal features between the two islands. The average vegetation height was significantly higher in the Dongtou island than in the Beiji island, whereas the incident light on ground was significantly less in the Dongtou island than in the Beiji island. As a result, environmental temperatures in full shade were substantially higher in the Beiji island than in the Dongtou island, although the temperatures did not differ in open ground between the two islands. The northern grass lizards distributed in the two thermally different islands also varied in field active body temperatures. In spring, field active body temperatures were not different in spite of the existed significant differences in operative temperatures and substrate temperatures between the lizard populations from two islands. In summer, field active body temperatures along with operative temperatures and substrate temperatures were all higher in the Dongtou island than in the Beiji island. In autumn, however, the field active body temperature and the associated operative temperature and substrate temperature were higher in the Beiji island than in the Dongtou island. The diversity and abundance of ground-dwelling invertebrates and therefore the food availability in Beiji island were greater than those in the Dongtou island. By contrast, activity pattern and preferred body temperature did not differ between the lizards from the two islands. Therefore, this study indicates that： （1） between-island differences are evident in temperature and food availability, which may partly account for the between-population differences in life histories of this species; （2） T. septentrionalis in these islands adopt behavioral thermoregulation rather than evolutionary shift in physiology to accumulate the seasonal and daily variations in thermal environments [Acta Zoologica Sinica 51 （5）： 797- 805, 2005].