VARIATION IN MORPHOLOGY, GAIT CHARACTERISTICS AND SPEED OF LOCOMOTIONIN 2 POPULATIONS OF LIZARDS

Locomotor behaviour varies between two subspecies of the Spanish wall lizard Podarcis hispanica. One subspecies inhabits the Columbretes isl ands, the other lives on the Spanish mainland. Size standardized volun tary speeds (as measured in unrestrained laboratory conditions) are lo wer in the island population (P h. atrata) than in the mainland popula tion (P h. hispanica). Maximal running performance (when chased) is mu ch higher in the mainland population than in the island population. Hi gh speed video recordings show that subspecies differ in gait characte ristics: individuals from the mainland modulate running velocity prima rily by modifying stride length, individuals from the island primarily by altering stride frequency. P h. hispanica's strategy for modulatin g speed probably allows this mainland subspecies to attain higher maxi mal speeds than the island subspecies P h, atrata. Theoretical conside rations suggest that at high speeds, P h. hispanica's running style is energetically more favourable, but this hypothesis awaits experimenta l verification. We suggest that the differences in locomotion efficien cy between the subspecies result from differences in predation pressur e between the mainland and the island. The mainland study site has a h igher predator diversity and offers less hiding opportunities to the l izards. (C) 1998 The Linnean Society of London.