Effects of Vegetation Loss on a Sand Dune Lizard

Habitat degradation in the form of vegetation loss often decreases the abundance of various species of reptiles (Fleischner 1994, Smith et al. 1996). Several reasons have been proposed for why vegetation loss should decrease abundance, including reduction of thermoregulatory patches, decreased prey availability, and increased predation from being in more exposed areas (Jones 1981, Norbury 2001). Vegetation loss could adversely affect lizards because they might be unable to escape lethal substrate temperatures (Adolph 1990, Carrascal et al. 1992). Vegetation loss may also decrease food availability, which could affect reptile abundance either directly or indirectly by affecting behavior. Individuals might compensate for reduced food availability by moving farther in search of prey or spending more time foraging, which might increase their susceptibility to predators (MacArthur and Pianka 1966, Hinsley 2000). Vegetation loss might additionally increase predation risk because fewer refuges are available. We examined the effects of vegetation loss by livestock grazing and agricultural practices on the abundance of the lizard Acanthodactylus longipes. To investigate the differences in abundance we found, we next compared body condition, thermoregulatory behavior, and activity patterns of lizards from unprotected and protected habitats. To test the hypothesis that vegetation loss affected thermoregulatory behavior, we compared the time that A. longipes spent thermoregulating by postural changes in unprotected and protected habitats. We expected that lizards in habitats with less vegetation might spend more time thermoregulating at higher temperatures by postural changes, while lizards in protected habitats might use vegetation more frequently. To test whether vegetation loss affected food availability or susceptibility to predation, we examined whether lizards in habitats experiencing vegetation loss moved greater distances or spent more time moving than in protected habitats. We assumed that if food availability were decreased, lizards would compensate by moving greater distances while foraging or spending more time foraging. This analysis also assumes that more active lizards are at higher risk of predation due to greater visibility. To provide an additional assessment of predation risk, we examined the distance from vegetation at which the lizard was observed. A. longipes is a common diurnal lizard that inhabits the sand dune deserts of North Africa and the Middle East; it thermoregulates by postural changes and by using vegetation (Attum 2004). A. longipes is ecologically and morphologically specialized for psammophile environments (Arnold 1981, Baha El Din 2001).