THE ECOLOGY OF THE SKINK MABUYA FRENATA IN AN AREA OF ROCK OUTCROPS IN SOUTHEASTERN BRAZIL

-Mabuya frenata is a relatively common skink in the region of Valinhos, Sao Paulo State, Southeastern Brazil, an area with a highly seasonal climate. The activity, thermal ecology, habitat use, and diet of this species were studied in the vincinity of Valinhos. Lizards were active throughout daylight periods, but the activity pattern differed among seasons, being more uniform in the rainy season than in the dry season. The mean body temperature of active M. frenata was 31.6 + 3.2 C and was correlated with air and substrate temperatures, although direct insolation may also be an important heat source for this lizard. Unlike environmental temperatures, the mean activity temperature of M. frenata did not differ among seasons, which, combined with field observations, suggests that this lizard thermoregulates. The microhabitat preferred for M. frenata was granitic boulders. The diet included a great variety of arthropods, although termites were the dominant items. The diet of M. frenata did not differ between sexes nor among seasons and was related to prey availability in the environment urnal of Herpetology, Vol. 32, No. 2, pp. 229-237, 1998 pyright 1998 Society for he Study of Amphibians and Reptiles e Ec logy of the Skink Mabuy frenata in an Area of Rock tcrops in South aste n Brazil Despite the fact that the scincid genus Mabuya contains about 13 South American species, most of which are abundant and widely distributed, few ecological studies have been carried out on these skinks in South America. Among the most recent of these are the autecological studies of Vitt and Blackburn (1991), and Vrcibradic and Rocha (1995, 1996) and those of Vitt and Blackburn (1983) and Blackburn and Vitt (1992) on reproductive patterns. Several other studies conCorresponding Author: E-mail: cfdrocha@uerj.br t in miscellaneous comments on the ecology of different South American Mabuya species (e.g. Fitch, 1968; Gallardo, 1968; Vanzolini and Rebouqas-Spieker, 1973, 1976; Vitt, 1991, 1995; Sazima and Haddad, 1992; Avila-Pires, 1995; Rocha and Vrcibradic, 1996; Vitt and Zani, 1996). The great majority of these studies have been carried out in Brazil, where most of the South American Mabuya species occur. Some aspects of the ecology of Brazilian Mabuya are fairly conservative among species: they usually have similar activity patterns (Vitt and Blackburn, 1991; Vrcibradic and Rocha, 1995, 1996), thermal ecol229 This content downloaded from 207.46. 13.160 on Mon, 17 Oct 2016 05:19:36 UTC All use subject to http://about.jstor. org/terms D. VRCIBRADIC AND C. F. D. ROCHA ogies, and body temperatures (Vitt and Blackbur, 1991; Vrcibradic and Rocha, 1995; Rocha and Vrcibradic, 1996) and consume a wide spectrum of prey (Vitt and Blackburn, 1991; Vitt, 1995; Vrcibradic and Rocha, 1995, 1996), although there is considerable interspecific variation in microhabitat preferences (Vrcibradic and Rocha, 1996). Mabuya frenata, the subject of this study, reaches an adult snout-vent length of 75-90 mm and occurs in open areas of South America, from central-western and southeastern Brazil to Bolivia, Paraguay, and Argentina (Peters and Donoso-Barros, 1986; Norman and Naylor, 1994). In spite of its wide distribution, published information on its ecology is scarce and mostly anecqdotal (Gallardo, 1968; Vitt, 1991; Sazima and Haddad, 1992). Apart from this fact, we chose to study this species because it is characteristic of "cerrado" habitats and, while there is some information available on the ecologies of Mabuya species from the Amazonian rainforest (Vitt and Blackburn, 1991), caatinga (Vitt and Blackbur, 1983; Vitt, 1995) and from coastal open sand-dune habitats (restingas) (Vanzolini and Reboucas-Spieker, 1976; Vrcibradic and Rocha, 1995; Rocha and Vrcibradic, 1996), there is a lack of ecological data on Mabuya species in cerrado areas [except for some few data on M. frenata in a cerrado area of central Brazil, in the context of the local lizard community (Vitt, 1991)]. Although our study area is an altered environment, it is located within the "cerrado" morphoclimatic domain and it houses a fairly large population of M. frenata. In this study, we investigate the thermal ecology, activity patterns, microhabitat use, and diet of M. frenata in an area where it is relatively abundant, and make comparisons with other Mabuya species. MATERIAL AND METHODS Study Area. -This study was conducted in a grassland area in Valinhos municipality (22? 56'S, 47? 55'W), Sao Paulo state, southeastern Brazil. The climate of the region is markedly seasonal, with a warm and rainy season from October to March and a cold and dry season from April to September (Van Sluys et al., 1994). The mean annual temperature is 20.7 ? 2.2 C and the total annual rainfall is 1300-1400 mm (Van Sluys, 1991; Van Sluys et al., 1994). This area has been used for some time as pasture and little is known about its original vegetation, which has been greatly altered during successive years of anthropic disturbance (Van Sluys, 1991). Vegetation of the area is presently dominated by species in the Malvaceae, Compositae, and Verbenaceae. There are numerous gr nitic boulders in the area, scattered along the surface of the hills. Collecting Methods and Analysis. -Lizards were collected monthly from December 1993 to December 1994 with an air rifle. Within 30 sec of capture, each lizard's body temperature (Tb) and the temperatures of the air (Ta; at 1 cm above the point where the lizard was originally sighte ) and of the substrate (T) on which it was sighted, were recorded. Body and air temperatures were measured with a Schultheis quickreading thermometer (read to the nearest 0.2 C); substrate temperatures were taken with a Schultheis bi-metal surface thermometer (read to the nearest 1.0 C). The time of collection of each lizard was recorded. Monthly observations of lizard activity were mad during 15-min periods within each hourly interval from 0700 to 1800 h. The number of active lizards counted during each interval was used to estimate daily activity patterns. Those observations were conducted in a sub-area adjacent to that where collections were made, but separated from it by about 100 m. No collections were made in that sub-area, because the continuous removal of lizards could affect the results of ou observations on their daily patterns of ac-