Effects of recent feeding on locomotor performance of juvenile Psammodromus algirus lizards

1. The addition of mass to an animal may reduce its locomotory capabilities and thus increase the predation risk. The effects of recent feeding on locomotor and escape performance of juvenile Psammodromus algirus lizards were examined. The consequences of a full stomach on the movement rate and locomotor patterns of lizards when walking spontaneously, and on their escape response from a simulated predator, were specifically analysed to determine whether juvenile lizards were able to compensate through modifications of behaviour for the possible locomotory difficulties derived from a full stomach. 2. The results indicated that feeding did not significantly affect the rate of spontaneous movements. However, voluntary locomotor patterns were partially affected. Thus, after feeding, individuals moved to significantly slower burst speeds, and also decreased significantly the frequency of pauses. 3. The escape performance was also significantly affected by feeding. In an individual escape run, lizards decreased their initial speed, although their burst speed did not change, and escaped over longer periods, stopping at greater distances. The endurance of the escape response in a continuous predator attack also decreased significantly after feeding, and lizards ran on less occasions and for shorter periods before becoming exhausted and hiding. 4. The possible consequences of reduced locomotory abilities on fitness are discussed. It is proposed chat, by changing their behaviour, juveniles may reduce these costs. This may allow them to consume large amounts of food at a time without incurring a higher predation risk.