Feeding habits of the lizard Tropidurus hispidus (Spix, 1825) (Tropiduridae) in a transitional Caatinga-Rocky Field Habitat in Northeastern BrazilAbstract
We investigated the diet of the endemic Tropidurid lizard Tropidurus hispidus in a Caatinga (the semiarid biome in Northeastern Brazil) area of Morro do Chapéu, BA, Brazil. Lizards (n = 20) were collected and euthanized. In the laboratory, stomach contents were removed, analyzed and classified by order, excepting for plant material. We then correlated the lizards’ morphological characteristics with the number, volume (in mm3), and the prey-size of the items. All lizards contained food items in their stomachs, encompassing a mix of arthropods, plant material, and a portion of vertebrate remains. The lizard’s diet featured a significant amount of plant material, comprising 50.1% in terms of number and 45.8% volumetrically. Among the diet items, flowers (63.6%), ants (47.0%), and beetles (33.0%) were the most frequent. The diet composition was found to be similar among males and females. There was no correlation between the morphological characteristics of T. hispidus and the number, length, or volume of the ingested prey items. Our data showed that T. hispidus in the Morro do Chapéu region is omnivorous and that plant material and hymenopteran and coleopteran insects are predominant in its diet.
Keywords
Diet; Lizard; Caatinga; Bahia; Tropidurus
INTRODUCTION
The genus Tropidurus stands as the most diverse within the Tropiduridae family, encompassing 23 valid lizard species (Costa & Bérnils, 2018). These species are distributed across several South American countries, including Brazil, Bolivia, Colombia, Uruguay, Venezuela, Guiana, French Guiana, Suriname, and Argentina (Frost et al., 2001). Despite the group’s wide distribution and diversity (Rodrigues, 1987), there is still a lack of ecological knowledge for some populations/species.
Tropidurus hispidus belongs to the torquatus group and is widely distributed in South America with populations occurring in open habitats in Brazil, Colombia (mainland), French Guiana, Guyana, Suriname and Venezuela (mainland) where it lives associated to semi-arid and savanna-like environments and rocky outcrop areas (Rodrigues, 1988; Vitt, 1995; Carvalho, 2013). Current knowledge about feeding habits of T. hispidus is primarily derived from studies of Amazonian populations (e.g.,Vitt, 1993; Vitt et al., 1996), in an area of rocky outcrops in Minas Gerais State (e.g.,Van Sluys et al., 2004), and in caatinga areas in northeastern Brazil (e.g.,Vitt, 1995). These studies usually describe T. hispidus populations as carnivorous or omnivorous (Vitt, 1993; Vitt, et al., 1996; Vitt, 1995). Only for a population from Minas Gerais State a notable consumption of plant matter (65.6%) was registered (Van Sluys et al., 2004). A similarly high consumption of vegetation has been observed in other species of torquatus group, such as T. torquatus (Rocha & Bergallo, 1994; Fialho et al., 2000; Teixeira & Giovanelli, 1999; Dutra et al., 2011; Siqueira et al., 2011, 2013), T. etheridgei (Cruz et al., 1998), T. erytrocephalus (Fontes, 2004), T. spinulosus (Cruz, 1998) and T. itambere (Van Sluys, 1995).
We studied the diet of a population of T. hispidus living in a transitional region between caatinga and “campos rupestres” (rocky fields) habitats, where it coexists with at least five other lizard species of similar size: two teiids, Ameiva ameiva (Linnaeus, 1758) and Ameivula occelifera (Spix, 1825), as well as three other Tropidurus species: T. cocorobensisRodrigues, 1987, T. semitaeniatus (Spix, 1825), and T. erythrocephalusRodrigues, 1987 (Menezes et al., 2011; Rocha et al., 2008). This study was carried out to answer the following questions: (1) What is the diet composition of T. hispidus and which prey items are dominant in its diet? (2) Is there a correlation between the number, volume, and mean size of ingested prey items and the morphological traits of T. hispidus? (3) Do the sexes differ in diet composition?
MATERIAL AND METHODS
This study was carried out in a transitional area between caatinga and “campos rupestres” habitats (rocky fields - see Eiten, 1992), in Morro do Chapéu (11°29′S, 41°07′W), Bahia State, northeastern Brazil. The municipality of Morro do Chapéu is situated in the northern portion of the Serra do Espinhaço mountain range, with altitudes around 1,000 m (Rodrigues, 1987).
The vegetation is predominantly herbaceous and shrubby on rocky and sandy substrates, dominated by Cactaceae, Fabaceae, Caesalpinaceae and Bromeliaceae (personal observation). The climate of the region is warm and dry. During the study period (27 November to 3 December 2000, rainy season), the mean air temperature was 29.3℃ and the relative air humidity was 48.9%. These values were obtained with a thermohydrometer, with measures taken hourly between 7:00 h and 17:00 h, under vegetation in the shadow, at a height of 1 m above ground.
Lizards were collected using rubber bands and a pellet rifle, during their period of activity. After collection, lizards were euthanized with ether, fixed in formalin (dilution of 1:9) for 48 hours and preserved in alcohol 70%. For each individual (prior to fixation) we measured the snout-vent length (SVL) and head width (HW) with a vernier calliper (to the nearest 0.1 mm).
In the laboratory, under a stereomicroscope, the lizards’ stomach contents were identified and the arthropods found were categorized to the taxonomic level of Order (or Family, in the case of Formicidae). Unidentified arthropod remains were grouped in a separate category “unidentified part of arthropods”, and were considered only for volumetric analyses. Each prey found in stomachs was measured in its width and length with a Vernier calliper (to the nearest 0.1 mm) and its volume (in mm3) was calculated using the ellipsoid formula: 4/3π (length/2) (width/2)2 (Dunham, 1983).
We counted the number of items and calculated the mean length (mm) and mean volume (mm3) of the five largest prey per stomach, and tested if these values were related to the morphological variables (head width and snout-vent length) of the lizards by a simple regression analysis (Zar, 1999). Due to the great variation in number, length and volume of food items, these variables were log-transformed prior to analysis. The differences in mean length, mean volume and number of preys consumed between adult males and females were tested by the Mann-Whitney test (Zar, 1999). We estimated an index of relative importance for each prey category in the diet by calculating the sum of the proportional values of volume (%), number (%) and frequency of occurrence (%) divided by three (see Howard et al., 1999).
The differences in frequency of occurrence and numerical proportion of each prey category consumed between males and females of T. hispidus were tested by Chi square test (Zar, 1999). The differences between males and females in body size (SVL) were tested using Student’s t test (Zar, 1999). The differences between males and females in the mean length, mean volume and mean number of preys consumed per individual (log-transformed) were tested by analyses of variance (One-Way ANOVA) (Zar, 1999).
All data were tested for homocedasticity of variances and for normality of distributions before performing statistical analyses.
RESULTS
Twenty T. hispidus were collected during fieldwork: eight males and 12 females. The mean snout-vent length of the lizards was 85.6 + 13.1 mm (range 70.2 - 117.2, n = 20). Males (mean SVL 90.7 + 17.7 mm, range 70.2 - 117.2, n = 8) and females (mean SVL 82.2 + 8.1 mm, range 71.7 - 95.1, n = 12) did not differ significantly in mean body size (t = 1.480, P = 0.156, DF = 18).
Tropidurus hispidus consumed 15 different types of food items, including arthropods and plant material and none of the stomachs analyzed was empty (Table 1). The diet of the lizards consisted mostly of arthropods, but there was also a high consumption of plant material. Hymenoptera Formicidae (95.0%), Coleoptera (85.0%) and flowers (80.0%) were the most frequent items in the diet of this lizard.
Absolute values and proportions (%) of the number, volume (in mm3), and frequency of occurrence, and values of the index of importance (Ix) for each category of prey in the diet of Tropidurus hispidus (n = 20) in an area of caatinga, Morro do Chápeu, Bahia, Brazil.
Numerically, the most important item was plant material (50.1%), followed by Hymenoptera Formicidae (36.0%). Volumetrically, plant material was the most representative item of the lizard´s diet and accounted for 45.8% of the total volume ingested. The items with the highest importance value (Ix) in the diet were plant material (63.6%), Hymenoptera Formicidae (47.0%) and Coleoptera (33.0%). One adult T. hispidus had a portion of a juvenile lizard’s tail in its stomach but, due to the advanced digestion state, it was not possible to securely identify the species or genus.
The SVL and the HW of lizards were not significantly related to the number (SVL: F1,18 = 1.634, P = 0.217; HW: F1,18 = 1.076, P = 0.314), mean length (SVL: F1,18 = 3.316, P = 0.085; HW: F1,18 = 2.649, P = 0.121) and the mean volume of the five largest items per stomach (SVL: F1,18 = 2.258, P = 0.150; HW: F1,18 = 0.316, P = 0.581) consumed by the lizards. The diets of adult males and females did not differ either in mean number (U = 45.000, P = 0.817, n = 20) or in mean volume (U = 50.000, P = 0.877, n = 20) of prey consumed. The diet of females was comparatively more diverse (15 types of items) than that of males (7 types of items). The proportion of each prey category consumed differed significantly among sexes, both in number (P = 0.014, X2 = 6.092) and in frequency of occurrence (P = 0.014, X2 = 6.023) (Table 2).
Percentages of number and frequency of occurrence of prey consumed by males and females of Tropidurus hispidus in a caatinga area, Morro do Chapéu, Bahia, Brazil.
DISCUSSION
The data indicate that Tropidurus hispidus has a diet comprising both arthropods and plant material, which categorizes it as an omnivorous feeder, similar to other species within the genus (e.g., T. torquatus,Fialho et al., 2000; T. itambere,Van Sluys, 1993; T. oreadicus,Rocha & Siqueira, 2008). In the diet of T. hispidus, ants, plant material and beetles dominated. Among these, plant material had the highest importance index value. The considerable presence of intact flowers in the stomachs (Table 1, n = 511) suggests that flower consumption was intentional and not accidental. The consumption of significant amounts of plant material, including flowers, leaves, fruits, and seeds, has been documented in the diets of other Tropidurus species (e.g.,Van Sluys, 1993; Vitt, 1993, Vitt et al., 1996; Cruz, 1998; Rocha & Siqueira, 2008; Fialho et al., 2000; Dutra et al., 2011; Siqueira et al., 2011, 2013).
According to Cooper & Vitt (2002), herbivorous lizards have adaptations for leaf digestion, such as specialized intestinal flora capable of breaking down cellulose. Conversely, omnivorous lizards lack such specialized adaptations, which often leads them to favor the consumption of flowers and fruits - plant parts that are easier to digest. In the case of omnivorous and herbivorous lizards alike, plants may play a significant role as a water source, particularly in environments with limited free water availability (Araujo, 1984; Rocha, 1996; Rocha, 2000; Menezes et al., 2011).
Some lizard species tend to include plants in their diet due to the nutritional benefits and moisture content they offer. An example is the liolaemid Liolaemus lutzae: in a study carried out in the beach habitat of Maricá restinga, this lizard selectively consumed only four out of 19 plant species available, which are those providing the most advantageous qualitative and quantitative characteristics (such as content of water, starch, sugar, and nitrogen) (Rocha, 1998). Nonetheless, our data underscores the significance of plant material in the diet of T. hispidus. However, the lack of studies analysing the qualitative value of plants to the lizards prevents us from understanding to what extent plant consumption is favored either as a water source or as a nutrient source.
Ants and beetles were the most important arthropods in T. hispidus’ diet. Conversely, prey items that generally aggregate within the environment, like isopterans, were present in low frequency, number and volume in the diet. A diet encompassing a diverse array of prey types, especially those with high mobility, aligns with the behavior of sedentary predators because they would prefer to prey on more mobile and active prey due to their comparatively reduced rate of movement in the habitat (Bergallo & Rocha, 1994). A high frequency of ant consumption has been noted in other T. hispidus populations, such as in Minas Gerais (97% of ants in its diet) (Van Sluys et al., 2004) and in Roraima (48% of the diet composed by ants) (Vitt et al., 1996).
The proportion of individuals with empty stomachs in a population can be used to evaluate the energetic balance in lizard’s populations (Huey et al., 2001; Flynn et al., 2020). At Morro do Chapéu, not a single T. hispidus displayed an empty stomach, suggesting that the species was keeping a positive energetic balance. This observation suggests a generalist and opportunistic feeding behavior by individuals of the population.
The diet of T. hispidus also included one unidentified lizard’s tail remains, implying that T. hispidus can be a source of mortality for young individuals of the prey species. In some lizard species, adult males may prey on juveniles of other or, in some cases, even their own species (Siqueira & Rocha, 2008). Predation holds substantial ecological significance, impacting the population dynamics of organisms and potentially influencing the population size of the prey species involved (Rocha & Vrcibradic, 1998).
Sexual dimorphism is a factor influencing the type, size, and amount of prey consumed, potentially leading to variations in dietary preferences among males and females (e.g.,Preest, 1994; Menezes et al., 2021). In Morro do Chapéu, the body size of male T. hispidus was similar to that of females, and there were no notable differences in the volume and number of preys consumed between sexes. However, the proportion of each prey category consumed by males and females differed, suggesting qualitative differences in feeding habits between the sexes. It would be interesting to undertake further studies to evaluate this distinction.
The lack of a relationship between morphological characteristics of lizards and the average size and volume of ingested prey is likely attributed to the substantial presence of ants and flowers in the diet. Ants and flowers constituted approximately 80% of the consumed items, and given their relatively consistent size, this might have reduced the overall variation in prey size within the diet, thus potentially minimizing the emergence of a significant correlation.
Tropidurus hispidus emerges as an omnivorous lizard, having a diet composed of both plant material and arthropods, similar to other species of Tropidurus. The high degree of plant consumption is particularly notable, even when compared to other omnivorous members of the genus. Furthermore, both males and females had no dimorphism in body size, which could possibly contribute to a similar diet among sexes concerning the number and volume of prey consumed. Nonetheless, a distinction in the proportion (evaluated by both number and frequency) of each prey category consumed by the two sexes was observed, indicating that qualitative differences in the diet between sexes exist. This study adds to the growing dataset of feeding habits of Neotropical Tropidurus lizards.
FUNDING INFORMATION:
ACKNOWLEDGMENTS:
This study is part of the “Programa de Ecologia, Conservação e Manejo de Ecossistemas do Sudeste Brasileiro” and of the “Projeto Ecologia de Répteis do Leste Brasileiro”, both of the Departamento de Ecologia, Instituto de Biologia, Universidade do Estado do Rio de Janeiro.
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