1. The thermal biology of ectotherms largely determines their abundance and distributions. In general, tropical species inhabiting warm and stable thermal environments tend to have low tolerance to cold and variable environments, which may restrict their expansion into temperate climates. However, the distribution of some tropical species does extend into cooler areas such as tropical borders and high elevation tropical mountains. Behavioural and morphological differences may therefore play important roles in facilitating tropical species to cope with cold and variable climates at tropical edges.

2. We used field-validated biophysical models to estimate body temperatures of butterflies across elevational gradients at three sites in southern China and assessed the contribution of behavioural and morphological differences in facilitating their persistence in tropical and temperate climates. We investigated the effects of temperature on the activity of 4,844 individuals of 144 butterfly species along thermal gradients and tested whether species of different climatic affinities -- tropical and widespread (distributed in both temperate and tropical regions) -- differed in their thermoregulatory strategies (i.e. basking). In addition, we tested whether thermally-related morphology, or the strength of solar radiation (when butterflies were recorded) were related to such differences.

3. We found that activities of tropical species were restricted (low abundance) at low air temperatures compared to widespread species. Active tropical species were also more likely to bask at cooler body temperatures than widespread species. Heat gain from behavioural thermoregulation was higher for tropical species (when accounting for species abundance), and heat gain correlated with larger thorax widths but not with measured solar radiation.

4. Our results indicate that physiological intolerance to cold temperatures in tropical species may be compensated through behavioural and morphological responses in thermoregulation in variable sub-tropical environments. Increasing climatic variability with climate change may render tropical species more vulnerable to cold weather extremes compared to widespread species that are more physiologically suited to variable environments.

We collected the dataset from butterfly transect walks in southern and southwest China. We collected butterfly behaviours by field observation. We logged the air temperature and solar radiation during the butterfly surveys. We used these environmental variables and morphological features of butterfly to build biophysical models to predict butterfly body temperature during basking in the sun. More details please see our assocaited paper.

Please check our paper and Readme file for the limitation of the data collected.