Evol Ecol Res 6: 63-75 (2004)     Full PDF if your library subscribes.

The race goes to the swift: fitness consequences of variation in sprint performance in juvenile lizards

Donald B. Miles*

Department of Biological Sciences, Ohio University, Irvine Hall, Athens, OH 45701, USA

e-mail: dmiles2@ohio.edu


Locomotor performance is a fundamental link between an animal and its environment. Considerable evidence has accumulated about the biomechanical, physiological and morphological causes of variation in sprint speed and endurance in animals. Yet little information is available about the ecological role of locomotion and its relationship to fitness. This is largely due to the difficulty of acquiring survivorship data in known demographic populations. To address the selective significance of locomotor performance, I estimated the covariation between sprint speed and survivorship of juveniles in a population of the lizard, Urosaurus ornatus. Selection analyses based on mark–recapture data revealed significant directional selection for burst velocity and stride length. Faster lizards with longer stride lengths realized a survival advantage over slower lizards regardless of size. Significant non-linear selection was detected on initial velocity and mean velocity. The selection surface for initial velocity was concave up, hence juveniles with intermediate values for initial velocity had lower fitness. Conversely, the selection surface for mean velocity was concave down, thus juveniles with intermediate values for mean velocity had higher survivorship. I hypothesize that the differences in sprint performance influence prey capture and predator escape. Faster lizards may also select warmer microhabitats during favourable conditions, which may enhance growth rates but entail higher risks of predation.

Keywords: body size, fitness, lizard, locomotor performance, survivorship, Urosaurus ornatus.

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