Temperature is a primary factor affecting ectotherm’s physiology and their ecological performance. As ectotherms, most reptiles are distributed in warm climate regions, but some of them have physiological adaptions to cold climate and inhabit mountain areas. A challenge for mountain oviparous (egg-laying) reptiles is to ensure that early-life stages can complete their development within a short activity season. Here, we investigate the suitability of nesting sites and model the hatching time of a high-elevation lizard, Takydromus hsuehshanensis (distribution 1800 m-3500 m elevation) in Taroko National Park, Taiwan. We first investigated the temperature-dependence of embryogenesis, and then employed a modeling approach to evaluate the thermal suitability of two main land covers (open land and heavy forest) for nesting at two elevations (2000, 3000 m elevation). We measured the developmental time of eggs under six temperature regimes in the laboratory and used these data to formulate a non-linear equation for the temperature-dependence on the developmental rate. We used a biophysical model, Niche MapperTM, to simulate the soil temperatures in open and heavy forested sites, which were then used as inputs to estimate the duration of embryonic development, as well as the suitability of nesting site.
Results/Conclusions
The results showed that the landscape forest cover affects soil temperature, hence embryonic development rate and suitability of nesting sites. The open landscape is predicted to be thermally suitable for nesting, as the substrate receives sunlight and provides warm enough conditions for embryonic development. Assuming that egg laying occurs in June (early summer), embryos are predicted to complete development in early August in open landscape, which is consistent with our field observations on nesting sites and the hatching time. In contrast, heavy forest is predicted to be too cold for embryo to complete development by the end of October (the end of activity season). Since most areas are covered with dense forests except for the grasslands located above the tree line, these results suggest that forest cover forms a cold barrier that restricts this species from moving downslope from their mountain-top grasslands habitats. Our study provides quantitative data to explain the negative impact of heavy forest on nesting sites of high elevation reptiles. The methodology can also be applied on other reptiles to investigate the quality of nesting sites in different landscapes.