Climate change effects on biodiversity: impacts of increased overwinter temperatures on UK reptiles

A comprehensive understanding of climate change effects on biodiversity would require a combination of knowledge from the impacts of increased overwinter and summer temperatures. However, existing studies are biased towards the effects of warm season getting warmer, though winter temperatures are increasing at a faster rate. Indeed, species' vulnerability to winter climate change has been rarely studied. Despite being a recent research track, existing studies on warming-winter effects on ectotherms (i.e. cold-blooded animals) revealed detrimental physiological effects that are unlikely to be observed in endotherms and somehow proved the vulnerability of terrestrial ectotherms. Ectotherms rely on ambient temperatures remaining within certain ranges to maintain critical physiological processes including growth and reproduction. As such, they are expected to react strongly to the thermal constraints imposed by climate change. Among ectotherms, reptiles are particularly vulnerable to rapid changes in environmental conditions given their often-limited dispersal abilities. Therefore, they are more likely to suffer higher extinction rates than other taxa due to climatic change.
The aim of the study is to investigate how rising winter temperatures affect the physiology and induce shift in the phenology and distribution of temperate reptiles.
To accomplish this, we will use the invasive wall lizard (Podarcis muralis, which hibernates during winter), and collate long-term data on UK reptiles to examine:
1. Physiological and behavioural shift under experimental winter conditions: We will assess the physiological effects of warming winter on wall lizards by measuring their reproductive success and recording their hormonal and behavioural response under experimentally manipulated thermal conditions during hibernation. This will help us to understand the effects of this aspect of climate change on individual fitness.
2. Distribution shifts associated with historical patterns of winter warming: We will examine the association of past thermal shifts - focusing on periods of significant winter warming - with the distribution of reptiles in the UK, then model their distribution. This will help us understand how species populations will interact under future climate scenarios.
3. Phenological shift associated with historical patterns of winter warming: We will test the association of past winter-warming periods on changes in the hibernation period and breeding season of UK reptiles, and then develop phenology models. In conjunction with studying distribution shifts, this will help us identify species vulnerable to climate change and priority species that urgently require conservation action.
In broad terms, this study will contribute to bringing a comprehensive knowledge on how species may respond to climate change, with a strong focus on increased overwinter temperature. It will bring additional information on the physiological effects of winter-warming on reptiles as well as the first information on behavioural effects. Moreover, it will document for the first time the phenological and distribution shift undergone by reptiles under mild wintering conditions. Such information is not presently included in estimates of future biodiversity loss under climate change but could be an important aspect to consider in predictions.