Meeting Abstract
Animals are faced with diverse substrates that they must negotiate during locomotion to effectively evade predators, forage, and find mates. Granular substrates, such as sand, are extremely common in nature, and represent a locomotor challenge because their particles move when a force is exerted on them. We studied how variation in substrate particle size and shape affects locomotion in a terrestrial generalist, the Steppe Runner Lizard (Eremias arguta), in the context of several ecologically-relevant material properties of the substrates. In particular, we studied the packing density, angle of repose, and load-bearing capacity of the substrates. We compared a series of six substrates composed of glass beads, which varied in particle size but had a uniform shape, and six natural rock substrates (sand and gravel), which varied in both particle size and shape. We found non-linear patterns in material properties relative to particle size, with density being greatest, angle of repose lowest, and load-bearing capacity greatest at intermediate particle sizes. We also found some evidence that gravel behaves differently from sand in natural, but not glass bead substrates. This was also evident in some of the locomotor performance and kinematic variables that we studied. Maximum velocity and acceleration was greatest at intermediate particle sizes, as were stride frequencies. Duty factor tended to decrease with increasing particle size or was lowest at intermediate particle sizes. Stride length and limb angles were unaffected by particle size. Hence, substrates with very fine or very coarse particle sizes appear to represent particularly large challenges to running lizards. This may be a result of ease of displacement of small particles and an uneven running surface associated with large particles.
