Sand grain size composition influences subsurface oxygen diffusion and distribution of an endemic, psammophilic lizard

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AbstractReptile species endemic to dune ecosystems worldwide possess morphological and behavioral adaptations for burying in sand. Specializations for burying and subsurface breathing among these animals are advantageous only where sand conditions permit. The patchy distributions of many psammophilic species are presumably due to the occurrence of suitable areas where attributes of the sand facilitate locomotion, burying, subsurface breathing and nesting. The endemic, dune‐dwelling Sceloporus arenicolus does not occur in areas where sand grain size composition is relatively fine, and the distribution of the species appears limited to areas with coarse‐grained sand. However, the exact mechanism by which this occurs is unknown. We hypothesized that subsurface breathing is inhibited in fine sand, and tested the prediction that fine sand restricts diffusion of oxygen. We compared oxygen diffusion rates in sand with grain size compositions matching sites where S. arenicolus was present (coarse sand) to diffusion rates in samples from sites where it was absent (fine sand). We found that samples with relatively coarse sand from sites where S. arenicolus was present had higher oxygen diffusion rates than samples with finer sand where S. arenicolus was absent. These results corroborated our prediction and support the hypothesis that subsurface breathing by S. arenicolus is constrained by fine sand. This is the first step in a line of research on the role of sand grain size composition in the life history of dune‐dwelling reptiles and more experiments can build on this study. Our results have broad implications for the conservation of all strictly psammophilic species by improving our understanding of the habitat elements necessary for their survival and persistence.