Variation in speed, gait characteristics and microhabitat use in lacertid lizards.

We quantified four gait characteristics (stride length, stride frequency, step length and floating distance) over a range of running speeds in 11 lacertid lizard species known to vary in maximal sprint speed and microhabitat use. For each species, we measured snout-vent length (SVL), body mass and hindlimb length. We tested which variables determine sprint speed, how each species modulates sprint speed and whether species occurring in different microhabitats differ in speed modulation strategy. In doing so, we aimed to test the assumption that sprint speed is correlated with hindlimb length through its effect on stride length. Variation in maximal sprint speed is determined by variation in both stride length and frequency, but those species that modulate their sprint speed mainly by altering stride length appear to attain the highest maximal speeds. At maximal sprint speed, long-limbed species take larger strides because of the positive effect of hindlimb length on step length and floating distance. However, when hindlimb length is statistically controlled for, mass has a negative effect on step length. None of the three morphological variables explained the interspecific variation in stride frequency at maximal sprint speed. Possibly, differences in physiological properties (e.g. muscle contraction speed) underlie the variation in stride frequency. The 11 species modulate their speed in different ways. Lacertids often seen in vertical microhabitats do not seem to be either pronounced stride length or frequency modulators. These species alter their speed by combining the two strategies. However, species occurring mostly in open and vegetated microhabitats are, respectively, stride length and stride frequency modulators. This difference in running style is substantiated by interspecific morphological differences.