Abstract

We determined group composition and foraging mode in a wild population of rupicolous rainbow skinks (Mabuya margaritifer) on rocky outcrops in a humid savannah of South Africa and examined diet, sexual dimorphism, and life-history traits in museum material. We also field-tested lizards for prey chemical discrimination. Males were larger than females in both body and head size. Both sexes reached maturity at 68 mm SVL, and females produced clutches of 2–9 eggs. Males excluded other males from their home range but shared overnight crevices with 1–4 females and 1–6 juveniles. Mabuya margaritifer were ambush foragers when only the amount of time spent moving (8%) was considered; however, other variables such as moves per minute (1.3) and average speed (0.01 m/s) suggest an intermediate foraging mode between active and ambush foraging for the population studied. Lizards spent most time on rock (81.5%) but also moved into vegetation (7.9%) and along the rock-vegetation interface (10.6%). Both sexes spent similar amounts of time in these microhabitats and were observed feeding in all three. Diet was dominated by termites, and overlap in prey types between sexes was high. In experimental tests for prey chemical discrimination, lizards tongue-flicked rarely, giving no indication of an ability to discriminate prey chemicals. Also, lizards observed in the field during focal observations performed few tongue-flicks. Based on these results, sexual dimorphism is best explained by sexual selection via male contest competition and not by ecological niche divergence.