Diel activity patterns of two syntopic range-restricted geckos suggest idiosyncratic responses to climate change

Abstract

Measures of activity patterns in relation to environmental conditions provide insights into ecologically driven requirements and climate preferences of species, particularly for ectotherms, due to the strong relationship between body temperature (T_b) and environmental temperatures. Lygodactylus incognitus (cryptic dwarf gecko) and Lygodactylus soutpansbergensis (Soutpansberg dwarf gecko) are range-restricted endemics to the Soutpansberg Mountains, South Africa, and have recently been shown to be potentially vulnerable to the effects of climate change. This prompted us to study the relationship between the thermoregulatory characteristics and environmental temperatures for these syntopic species. Active geckos (i.e. those outside of a refuge) and environmental variables were recorded during scan surveys across two seasons. Binomial logistic regressions were used to predict and explain activity based on presence/absence measures and environmental variables for each species. Of the variables measured, air temperature (T_a) was the main predictor of activity for both species. Cryptic dwarf geckos were active in cooler T_a than warmer temperatures in comparison to Soutpansberg dwarf geckos. Cryptic dwarf geckos are thus well adapted to temperate conditions. Soutpansberg dwarf geckos appear well adapted for warmer conditions, as they were more likely to be active at higher T_a. Our findings suggest that both species will alter their daily activity times in response to changing climate, but that the cryptic dwarf gecko is likely to be more negatively impacted than the Soutpansberg dwarf gecko, due to their affinity for cooler temperatures and avoidance of the hottest temperatures exhibited during the study period. Therefore, although these broadly sympatric, syntopic, range-restricted species are closely related and have similar life histories, they occupy different thermal niches and are likely to respond to climate change idiosyncratically. Our findings caution against the overuse of proxy species in predicting species geographic distribution changes in response to climate change.