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.
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.