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

摘要

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 availability 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].