Results suggest that the balance between natural selection for stealth and sexual selection for conspicuousness may vary among lizard populations. In SL, the habitat is mostly gray rock, so the SL collared lizard population has a small chance of hiding. For this reason, male SL lizards are a dull greenish-brown color that resembles that of females and rocks. In GM, the context is more complicated, so that male lizards are more visible than rock lizards and females (Macédoine et al. 2004). More than twice the number of models was exploited in SL compared to GM, showing that natural selection more effectively constrains sexual selection for colored males in SL than in GM. This reveals why SL males are duller than GM collared lizards. This appears to be different for the WM population. These MW male populations are more visible than GM and SL males; however, MW experiences the greatest predation pressure among the three sites. Investigators have suggested that WM males may appear conspicuous outside of their environment, but may actually be enigmatic within its complex environment (Baird et al. 1997; McCoy et al. 1997). When this idea was tested, mixed support was found. They found that some areas of the site made MW lizards conspicuous (flowers, lichens, and vegetation) and other areas made the lizards more inconspicuous (rocks and other vegetation) (Macédoine et al. 2004). Another reason why MW male lizards may be more visible even though the population is under high predation pressure in the tall grass zone of the MW. These tall grasses provide excellent concealment from visually hunting snakes, such as the whip. Because WM collared lizards may appear...... middle of paper ......JM, Husak, JF, Brandt, YM, Lappin, AK & Baird, TA 2004: Sexual dichromatism and color sharpness in three populations of collared lizards (Crotaphytus Collaris) from Oklahoma, USA. J. Herpetol. 38, 343—357. Marshall, NJ 2001. Adjustable color vision in a mantis shrimp. Nature, 411, 547.McCoy, JK, Fox, SF & Baird, TA 1994: Geographic variation in sexual dimorphism of Crotaphytus Collaris. Southwest Nat. 39, 328—335. Endler, JA 1990: On the measurement and classification of colors in studies of animal color patterns. Biol. J. Linn. Soc. 41, 315-352.McCoy, JK, Harmon, HJ, Baird, TA & Fox, SF 1997: Geographic variation in sexual dichromatism of Crotaphytus Collaris. Copeia 1997, 565—571. Pocklington, R. & Dill, LM 1995: Predation on females or males: who pays for bright male traits? Lively. Behavior. 49, 1122—1124.