Dieta do lagarto Tropidurus torquatus (Wied, 1820) (Tropiduridae) na restinga de Grussaí, RJ: tamanho e sexo afetando a composição da dieta e importância de presas

Abstract

Species of the genus Tropidurus are heliophilous, oviparous and considered omnivorous. They frequently use ambush foraging strategies, being considered sedentary and opportunistic. Tropidurus torquatus presents sexual dimorphism in size, with males larger than females. It has a diet based on arthropods, mainly active preys, and plant material, however, the proportions varies amongst populations. In general, besides the environmental characteristics, one of the possible factors of variation in the diet is the age. Therefore, the body size, head and mouth increase with age: adults tend to have a more diverse diet than young individuals. In the present study, we analyzed the diet of T. torquatus, characterizing it at a population level, and studying the differences in diet amog male, female (pregnant and non-pregnant) and young individuals, in a sand coastal area (restinga de Grussaí) in the state of Rio de Janeiro, southeastern Brazil. For data collection, it was carried samplings on four vegetation zones in restinga area from 6 am to 9 pm. Lizards were collected (N = 69) and taken to the laboratory to determine body and mouth sizes, sex, and age (young or adult). Stomachs were removed and analyzed on a microscope, recording the diet items, in number, volume and frequency of each item. The T. torquatus diet was characterized by a large variety of food categories (N = 28). Arthropods were the majority, being Formicidae the most consumed food item in terms of number and frequency, and Coleoptera in volume. We analyzed the proportion of plant material and preys with fossorial habit in the diet, which presented a significant amount of leaves and fruits, and preys with fossorial habit, allowing us to infer about the foraging strategy employed. Through the Variance Analysis test, we found differences in number and frequency of food items for the three population classes (adult males, adult females and young individuals). In terms of volume, the highest differences found were between males and females, and also females and young individuals. In terms of the importance (relative importance índex) of the items, there was no difference among classes, and using the Simpson diversity index (Simpson, 1949), the young individuals presented items food diversity smaller than adults. Through an Exponential Regression, we found a positive relationship between mouth width and the size of the largest prey ingested, with males consuming the largest preys. The results suggest that T. torquatus is an opportunistic lizard and has a general diet consisting mainly of arthropods and plant material, despite the latter being the less consumed item by young individuals. Pregnant and nonpregnant females differed in diet composition, suggesting different foraging intensities. We believe that the population presented an intermediate foraging strategy with a tendency to ambush, aiming at the optimization of conflicting demand between energy expenditure by foraging and energy acquisition through food ingestion, as proposed by the Theory of Optimum Foraging.