Living on the edge: thermoregulation at the niche margin in the Bedriaga’s rock lizard

Thermoregulation is essential for ectotherms but its relative cost, especially under ongoing climate change, depends on the thermal quality of habitats. Populations at the warm margin of a thermal niche could be negatively affected by environmental temperatures that approach the limits of a species’ thermoregulation capacity. This study aims to define the thermal niche of the Bedriaga’s rock lizard, Archaeolacerta bedriagae, a rock-dwelling species endemic to the Corsica and Sardinia islands (western Mediterranean Sea), and to investigate its thermoregulation effectiveness at the warm edge of its niche. We collected data on climate, body temperature, and microhabitat temperature throughout the species’ range to characterize its thermal niche. We found that A. bedriagae does not occupy the entire climatic space available across its distribution range; rather, it selects temperate climates. Remarkably, thermoregulation effort increases when the habitat thermal quality decreases towards warmer sites. Populations at the warm edge of the thermal niche show the best thermoregulation effectiveness, but they are also more sensitive to the effects of climate change as they may already be at (or beyond) the species’ maximum thermal capacity under the current conditions. We observed such a pattern at the extreme hot side of the thermal niche. This study provides key information on the thermoregulatory response of A. bedriagae to ongoing climate change that can be useful to identify populations facing a higher extinction risk either currently or in the near future.