Heterochrony and Evolution of Sexual Dimorphism in the fasciatus Group of the Scincid Genus Eumeces

Abstract

-We studied diet composition of Lacerta lepida in a sample of 325 specimens from central Spain. This large lacertid lizard feeds predominantly on Coleoptera, but also consumes other arthropods, snails, small vertebrates, and some plant material. Composition of the animal fraction of the diet and trophic diversity were virtually identical in adult males and females. Juveniles fed upon a restricted number of prey types which were small in size, whereas adults consumed a large number of prey taxa, covering a wider range of prey sizes. Trophic segregation among individual lizards was highest in the smaller size classes. The incidence of plant material increased with lizard size and was highest in males, but it never represented a substantial fraction of the total diet. The contribution of small vertebrates to total prey numbers also increased with lizard body size. Our results indicate that vertebrates are of marginal numerical importance to the diet of L. lepida. Most lizards feed primarily on arthropods, although some species have adopted a diet consisting mainly of molluscs, plant material or small vertebrates (see Greene, 1982). Insectivorous lizards are often opportunistic feeders, eating any suitable sized arthropods. Hence, diet composition has been shown to exhibit seasonal or (micro)geographic variation, in response to a shift in prey availability which is either presumed (e.g., Avery, 1966; Mou and Barbault, 1986; Arnold, 1987) or documented (e.g., Ballinger and Ballinger, 1979; Stamps et al., 1981; 4 Present Address: University of Antwerp (U.I.A.), Department of Biology, Universiteitsplein 1, B-2610 Wilrijk, Belgium. Mou, 1987). Body size is another factor that influences prey choice and diet composition (Pough, 1973). Although most evidence for a relation between body size and dietary composition derives from interspecific comparisons, ontogenetic changes in prey choice within single lizard species have been described (see Pough, 1973; Greene, 1982). European lizards of the family Lacertidae are basically insectivorous, although some forms occasionally eat other invertebrates, small vertebrates or plants (see Arnold, 1987). Lacerta lepida, the largest European lacertid (adult snoutvent-length 140-220 mm), is a diurnal, heliothermic, ground-dwelling lizard that is found in a variety of mediterranean habitats throughout most of Spain and Portugal, in southern 30 This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 07:29:21 UTC All use subject to http://about.jstor.org/terms