Highlighting potential effects of microsite distributions in predictions of lizard vulnerability to climate change

Behaviour is one of the principal mechanisms that ectotherms use to buffer climate variation, including extreme events that can negatively impact their survivorship. In addition to behaviour, several other mechanisms can play a role in buffering these climatic changes, including plasticity of physiological traits, the ability to quickly adapt to rapid changes and the potential to disperse. Therefore, given the multitude of potential organismal responses, predicting population persistence and extinction risks in future climate scenarios, both at regional and global scales, remains a challenging task.

A basking cape girdled lizard is shown next to two copper models with differing reflectance

In lizards, microsite or operative temperatures are typically measured with copper models that resemble the species investigated by matching the shape, size, body posture and skin reflectance of the animal. Here, a basking cape girdled lizard Cordylus cordylus is shown next to two copper models with differing reflectance, to record operative temperatures in the field.

Sinervo and colleagues (2010, Science 328) recently undertook an unprecedented documentation of lizard population extinctions across the globe and devised a model that predicts lizard extinctions. Briefly, the model incorporates body temperature of lizards in the field and mean maximum environmental temperature during key energetically demanding periods (reproductive seasons) to predict the cumulative hours during which lizards cannot maintain activity, named ‘the hours of restriction’ (hr). This parameter hr was strongly correlated with reported population extinctions regionally in Mexico, and globally, across five different continents with additional adjustments made to account for differences among lizard families.

In a recent technical article published in the journal Science, C·I·B core team members Susana Clusella-Trullas and Steven L. Chown commented on the approach used by Sinervo and colleagues. The C·I·B team pinpointed some drawbacks originating from using a variable such as hours of restriction that is based on the mean maximum environmental temperature when extrapolating the model at global scales and in future climate scenarios. In particular, their comment addresses the availability of microsites (or more typically called operative temperatures) in space and time in the environment used by lizards and how the frequency distribution of operative temperatures may change dramatically depending on the habitat-type and species studied, ultimately affecting the hours of restriction. These effects are depicted by using hypothetical shapes and heights of frequency distributions and are relevant for models of extinction in current and future climate scenarios.

This technical comment highlights the importance of accounting for potential temporal and spatial variability of species-relevant microsites when modelling ectotherm thermoregulatory constraints and will likely influence future forecasts of reptile vulnerability in face of climate change.

Read the article:

Clusella-Trullas, S., Chown, S.L. 2011. Comment on “Erosion of lizard diversity by climate change and altered thermal niches”. Science 332: 537.