Getting Up to Speed: Acceleration Strategies in the Florida Scrub Lizard, Sceloporus woodi

Small animals typically rely on quick bursts and intermittent pauses when moving in the wild. Hence, the study of acceleration capacity is important for understanding the ecology and evolution of locomotor performance. In this study, we investigate intraspecific variation in the acceleration capacity of a small lizard (Sceloporus woodi). To quantify animal acceleration performance, the momentum-impulse theorem is applied to data collected from high-speed video recordings of individuals accelerating from a standstill and over a subsequent distance of 0.4 m. Unlike earlier studies, the momentumimpulse approach allows one to directly and precisely quantify the per step contribution to acceleration capacity. Like other small vertebrates, we show that S. woodi is capable of accelerating to near maximum speeds (∼2 m s^-1) within ∼0.4 m and needs only a few steps (at least five) to achieve maximum speed. However, considerable intraspecific variation in acceleration capacity exists; individuals take different numbers of steps (two to five steps) over the first 0.4 m, and only some individuals (10 of 19) reach their maximum speed over the first 0.4 m. Only acceleration performance in steps 1 and 2 is predictive of running speed at 0.4 m; accelerations in steps 3, 4, and 5 are not related to individual differences in speed. Individual variation in acceleration strategy is considerable, with individuals using one of three strategies to reach maximum speed. Muscle mass-specific power during acceleration approaches the maximum power output measured for lizard hindlimb musculature (∼900 W kg ^-1), suggesting that S. woodi accelerations approach the limit of their musculoskeletal system. This study highlights the utility of the momentum-impulse approach to study acceleration performance and the importance of elucidating the per step contribution to acceleration capacity.