Trophic Structure and Dietary Overlap in the Sympatric Skinks Trachylepis punctatissima and Trachylepis varia From Central South Africa

Abstract

Diet diversity and overlap was investigated in the sympatric skinks Trachylepis punctatissima and Trachylepis varia from central South Africa using stomach and intestinal contents of museum specimens. Simpson's Index and the Shannon–Wiener Index were used to determine their food niche breadths and Pianka's Index to determine the extent to which they shared the food resource. Food items were identified from head capsules, mouthparts and appendages to order level. The two species contained similar prey types with T. varia having the wider niche breadth. Females also had wider niche breadths than males and isopterans were present in significantly higher quantities than the rest of the food items in both species. Larvae were found in both, but arachnids only in T. varia. Trophic niche overlap between the two was fairly high (Pianka's Index, 0.6915) and therefore did not support the hypothesis that similar species sharing a food resource should have well differentiated diets to reduce competition. This finding however requires further verification as the two species may consume different species of the corresponding orders identified. Intraspecifically trophic niche overlap between the sexes was low (T. punctatissima, 0.3889; T. varia, 0.4633) suggesting strong competition for the food resource. Notably lower niche breadth in males compared to females may be due to morphological and behavioural differences and should be further investigated.