Produção Nacional
Revisado por pares
Diet of Leptodactylus ocellatus (Anura: Leptodactylidae) from coastal lagoons of Southeastern Brazil
2003; Asociación Herpetológica Argentina; Volume: 17; Linguagem: Inglês
ISSN
1852-5768
AutoresRogério L. Teixeira, Davor Vrcibradic,
Tópico(s)Wildlife-Road Interactions and Conservation
ResumoR. L. TEIXEIRA & D. VRCIBRADIC: Diet of Leptodactylus ocellatus in Brazil 112 (Heyer et al., 1990). In spite of its very wide distribution, relatively few ecological studies have been done regarding this species. Those studies have dealt mainly with aspects of reproduction and growth (Cei, 1948; Lima and Verani, 1984), behavior (Vaz-Ferreira and Gerhau, 1975), and food habits of tadpoles (Lajmanovich, 1994), juveniles (Lajmanovich, 1996) and adults (Strussmann et al., 1984). The latter two studies, carried out on an Argentinian floodplain and in Brazilian Amazonia, respectively, indicated that L. ocellatus has a very generalized diet, composed mainly by a wide variety of arthropodan taxa. Nevertheless, data on the food habits of this species are lacking for other South American biomes. Herein some data is presented on the feeding habits and trophic ontogeny of L. ocellatus from three coastal lagoons in Espirito Santo state, Southeastern Brazil, within the Atlantic Forest biome. MATERIAL AND METHODS Fieldwork was carried out in three coastal lagoons in the municipality of Anchieta, Espirito Santo state, Southeastern Brazil: Barragem Norte, Lagoa de Mae-Ba and Lagoa de Ubu, all located close to each other (20o 46S, 40o 35W). Lagoa de Mae-Ba is the largest of the three, with the other two being about the same size. Barragem Norte is an artificial pond, built to receive iron ore powder from the locality of Germano, Minas Gerais state, through a water duct that stretches ca. 380 km. It has extensive vegetation at both the margins and inside (compared to the other two lagoons), which is represented mainly by Typha aff. dominguensis (Typhaceae), Nymphaea sp. (Nymphaeaceae), Eleocharis sp., and Lagenocarpus aff. rigidus (Cyperaceae). Typha aff. dominguensis is the dominant species at both the Lagoa de Mae-Ba and the Lagoa de Ubu. Those two lagoons, unlike Barragem Norte, are connected to the sea and formed by brackish water. The environment around the three lagoons is, for the most part, greatly disturbed and characterized by arbustive vegetation (locally called «capoeira») and Barragem Norte is also close to an eucalyptus plantation. Specific collection sites were the same throughout the study, each at the margin of one of the lagoons. Average monthly rainfall in the region of Anchieta is 1144 mm, with a monthly maximum of 194 mm and a monthly minimum of 43 mm (Moraes, 1974). Average monthly temperature during the period of study was 23.1oC. Collections were conducted bimonthly, from November 1999 to September 2000. Frogs were collected by hand, mostly at the margins of the lagoons. Collections were made during one night each month, always between 20:00 and 22:00 h, with sampling effort being the same for each locality. Frogs collected were killed in 10% alcohol, and transferred to 10% formalin. After a week, the specimens were washed and preserved in 70% alcohol. Voucher specimens of L. ocellatus were deposited at the Museu de Biologia Prof. Mello Leitao (MBML 1241-2, 1245, 1942-3, 1946). In the laboratory, frogs had their snout-urostyle length (SUL) measured with a caliper (to the nearest 0.1 mm). After those procedures, the animals were dissected and sexed. The stomachs of all frogs were removed, and all food items found were spread on a Petri dish and identified under a stereomicroscope. Prey were identified to Order, counted, and had their length measured with a caliper and their wet mass taken with a digital balance (0.1 mg precision). Frequency of occurrence, number of prey, and total prey mass were calculated for each prey category. Cuad. herpetol., 17 (12): 111118, 2003 113 The relationship between the length of the largest prey item in the stomach and frog size (SUL) was tested using a simple regression analysis; for this analysis, we did not consider prey items that were too digested and/or fragmentary to have their original length estimated with reasonable accuracy. We also performed a cluster analysis (UPGMA; Krebs, 1989) based on the Euclidean distances in order to detect possible quantitative differences in the diet according to the size (SUL) range of frogs. Only the data on relative prey mass (log10 transformed) were used in this analysis. RESULTS Fifty-seven specimens of L. ocellatus were collected, 44 of them at the Barragem Norte, seven at the Lagoa de Mae-Ba and six at the Lagoa de Ubu. Frogs ranged from 18.5 to 100.4 mm in snout-urostyle length (SUL). Thirtyone specimens were males, 21 were females and five were juveniles whose sex could not be determined. Of the 57 stomachs examined, only four (7.0%) were empty. Data on the diet of L. ocellatus at the study area are summarized in Table 1. Leptodactylus ocellatus preyed upon a great variety of small animals, including vertebrates. The diet was dominated by arthropods, with adult beetles being the most frequently consumed food item, followed by beetle larvae, ants and cockroaches. Termites dominated the diet numerically (though only two frogs had eaten this prey type), followed by adult beetles. Crickets were the predominant items in terms of percentage of the total prey mass ingested. Among vertebrates, frogs, tadpoles and one small fish (Poecilia vivipara) were represented in the diet of L. ocellatus. The amphibians found in the stomachs were one Hyla albomarginata (SUL= 35.2 mm), one Physalaemus crombiei (SUL= 20.1 mm), a juvenile L. ocellatus (SUL= 23.1 mm), and three unidentified tadpoles. Number of individual prey per stomach varied from 1 to 25 (mean = 2.5 ± 3.8). Individual prey consumed varied in size from 1.5 to 35.2 mm. Maximum prey length was positively and significantly related to frog SUL (R2 = 0.59, p 90 .0 70 .0-89 .9 50 .0-69 .9 30 .0-49 .9 <30 .0 S V L ( m m ) Fig. 1. Dendrogram representing the differences in diet composition (based on relative contribution in total prey mass for each prey category) among size classes of Leptodactylus ocellatus at Anchieta, Espirito Santo, Brazil. R. L. TEIXEIRA & D. VRCIBRADIC: Diet of Leptodactylus ocellatus in Brazil 114 of the diet. Diets of the remaining size classes were generally dominated (in terms of relative mass) by orthopterans, frogs and adult beetles. DISCUSSION Specimens of L. ocellatus representing a broad range of body sizes were collected throughout the period of study. Most individuals were collected at Barragem Norte, an artificial lagoon with a greater diversity of vegetation than Lagoa de Mae-Ba and Lagoa de Ubu. Probably, the denser vegetation around and within Barragem Norte provides a more adequate habitat for other anuran species and a variety of invertebrates, which are all potential prey for L. ocellatus, as well as a greater diversity of sheltering and reproducing sites for L. ocellatus. More importantly, Barragem Norte is a strictly freshwater «lagoon» whereas Lagoa de Mae-Ba and Lagoa de Ubu contain brackish water. Considering the usual intolerance of salinity of Table 1. Representativeness (in absolute numbers and percentages) of prey types found in the stomach contents of the frog L. ocellatus from three coastal lagoons of the Municipality of Anchieta, Espirito Santo, Brazil. F = frequency of occurrence; N = number of prey; M = mass of prey. PREY TYPE F %F N %N M %M INSECTA Blattodea 8 14.8 9 8.3 685 3.8 Coleoptera (adults) 12 22.2 18 16.7 1890.1 10.5 Diptera 1 1.9 1 0.9 3.9 <0.1 Hemiptera Belostomatidae 3 5.6 3 2.8 1236.7 6.8 others 1 1.9 1 0.9 9.2 0.1 Hymenoptera (ants) 9 16.7 12 11.1 61.8 0.3 Isoptera 2 3.7 22 20.4 1198.8 6.6 Lepidopteran larvae 1 1.9 5 4.6 1136.1 6.3 Coleopteran larvae 11 20.4 11 10.2 156 0.9 Odonata 1 1.9 1 0.9 595.8 3.3 Orthoptera 4 7.4 12 11.1 3906.3 21.6 MYRIAPODA Diplopoda 2 3.7 2 1.9 1697.4 9.4 ARACHNIDA Araneae 3 5.6 3 2.8 1370.7 7.6 ANNELIDA Oligochaeta 1 1.9 1 0.9 217 1.2 AMPHIBIA (ANURA) Hyla albomarginata 1 1.9 1 0.9 212.4 1.2 Leptodactylus ocellatus 1 1.9 1 0.9 1640.1 9.1 Physalaemus crombiei 1 1.9 1 0.9 1348.7 7.5 Tadpoles 2 3.7 3 2.8 165.6 0.9 PISCES (TELEOSTEI) Poecilia vivipara 1 1.9 1 0.9 309 1.7 OTHERS Plant remains 2 3.7 230.7 1.3 Detritus 5 9.3 10.8 0.1 TOTAL 108 100.
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