Extreme spatial confinement and high site fidelity in a crevice-dwelling lizard with a minimal home range

Body size has traditionally been regarded as a key predictor of home-range extent. However, it remains unclear whether habitat specialisation can alter the expected allometric relationship between body size and home range. Crevice-dwelling lizards of the genus Xenosaurus provide an excellent system for addressing this question due to their extremely restricted habitat use. Using Bayesian generalised linear models-which allow explicit comparison of alternative hypotheses-we focused on (I) characterising the spatial behaviour of X. platyceps, (II) testing whether the home range of X. platyceps deviates from allometric expectations within a comparative dataset of 100 lizard species, and (III) evaluating whether the thermal environment helps explain its reduced movement.

We report one of the smallest and most temporally consistent home ranges documented for an adult lizard. It was observed in a female X. platyceps that remained in the same crevice for more than 43 months, with an estimated minimum home range of 0.014 m². Bayesian allometric analyses showed that the observed value was over two orders of magnitude smaller than predictions based on body-size allometry. Thermal modelling revealed no differences between body, ambient and crevice temperatures. Moreover, body temperature was best explained by crevice temperature. These results indicate a thermally homogeneous microhabitat and thermoconforming behaviour. This pattern may help explain the reduced movement observed in X. platyceps.

Our findings suggest that, in species with extreme habitat specialisation, home-range extent may be better explained by environmental stability and foraging strategy than by the classical body-size relationship. These results highlight the potential for tight microhabitat coupling to decouple spatial use from allometric expectations. Moreover, because microhabitat specialists are particularly vulnerable to habitat fragmentation and refuge loss, it is essential to consider spatial use patterns when assessing conservation status and designing management strategies.