Diet of Leptodactylus Ocellatus (Anura: Leptodactylidae) from a Cacao Plantation in Southern Bahia, Brazil

Herpetology Notes, volume 2: 9-15 (2009) (published online on 16 February 2009) Diet of Leptodactylus ocellatus (Anura: Leptodactylidae) from a cacao plantation in southern Bahia, Brazil Mirco Solé1*, Iuri R. Dias1, Erika A. S. Rodrigues1, Euvaldo Marciano-Jr1, Samuel M. J. Branco1, Kaoli P. Cavalcante1 and Dennis Rödder2,3 Abstract. We studied the diet of Leptodactylus ocellatus in a cacao plantation in southern Bahia state, Brazil and compared our results with data available from populations inhabiting natural and human modified habitats. Stomachs of 117 specimens were flushed whereby 77 stomachs revealed at least one prey item. Our results indicate that L. ocellatus consumes a great variety of food items at the study site, whereby Lepidoptera larvae, Coleoptera and Araneae dominated its diet. The presence of vertebrates including Teleostei and Anura in the diet revealed in previous studies was confirmed, although these items made up only minor parts of the diet. The index of relative importance showed that the diet of L. ocellatus was dominated by Lepidoptera larvae, followed by Coleoptera and Araneae. The Levins index observed in our samples was 8.51 and the standardized Shannon-Weaver index was 0.56. Apparently, the structure of the trophic niche of L. ocellatus is not affected by habitat alteration. The present study provides evidence for the opportunistic feeding behaviour and broad trophic niche breadth of L. ocellatus. Keywords. Amphibia, diet, trophic niche, cacao plantation, predation. Introduction whereby the genus Leptodactylus currently comprises Trophic interactions are a crucial component of life 76 species mainly distributed in South America (Frost, history strategies and contribute to the population 2008). Compared to other members of the genus, regulation (Duellman and Trueb, 1994; Wells, 2007). Leptodactylus ocellatus (Fig. 1) is a large nocturnal frog, In the Neotropics, habitat loss is still the primary which is widely distributed throughout South America threat to amphibian populations (Young et al., 2001; east of the Andes (Cei, 1980). The species inhabits all Stuart et al., 2004). Other indirect effects associated to varieties of ponds, rivers and even lakes and can often landscape fragmentation may cause alteration of trophic be found in strongly anthropogenized areas. Heyer, interactions, due to changes in microclimate, causing Caramaschi and de Sá (2006) recently designated a abundance variations in available prey items, what neotype for this species and stated that there are both might contribute to the decline of amphibians (Carey et reproductive and molecular differences that suggest the al., 2001; Young et al., 2001). A profound knowledge presence of more than one species under the name L. about trophic relationships in tropical communities is ocellatus. essential for the development of successful conservation Regarding L. ocellatus, previous studies have mainly strategies. An assessment of possible shifts in trophic dealt with growth, reproductive (Vaz-Ferreira and niches of species inhabiting natural and human altered Gehrau, 1975), behavioral aspects (Strüssmann et al., habitats is currently lacking for the vast majority of 1984), food habits of tadpoles (Lajmanovich, 1994) and anuran taxa. juveniles (Lajmanovich, 1996). The diet of L. ocellatus The family Leptodactylidae is distributed from the has been studied in several Neotropical countries extreme southern USA throughout tropical Mexico, (Strüssmann et al., 1984; Teixeira and Vrcibradic, 2003; Central America and South America (Frost et al., 2006), França, Facure and Giaretta, 2004; Maneyro et al., 2004; Sanabria, Quiroga and Acosta, 2005) and in several populations the species has been found to be a potential 1 Department of Biological Sciences, Universidade Estadual predator of amphibians (Teixeira and Vrcibradic, 2003; de Santa Cruz, Rodovia Ilhéus-Itabuna, km 16, 45662-000 França, Facure and Giaretta, 2004; Sanabria, Quiroga Ilhéus, Bahia, Brazil; e-mail: [email protected] and Acosta, 2005). 2 Zoological Research Museum Alexander Koenig, Department Our study provides data on the diet of L. ocellatus from of Herpetology, Adenauerallee 160, 53113 Bonn, Germany a cacao plantation in southern Bahia. We report some 3 Trier University, Department of Biogeography, 54286 Trier, Germany prey categories that have not been previously identified * corresponding author as part of the frog’s diet and we discuss our data with 10 Mirco Solé et al. available data from both natural and human modified to vials, fixed in 70% ethanol and later analyzed under a habitats in Uruguay, Peru, the Brazilian Pantanal and stereomicroscope. Prey items were classified following order the Brazilian states of Espírito Santo, Minas Gerais and level, with exception of Hymenoptera, which were classified as Formicidae and Non-Formicidae. Completely preserved Rio Grande do Sul. items were measured and had their volume calculated using 2 4S LW§· Material and methods V ¨ ¸ 3 2© 2 ¹ Sampling Frogs were collected manually from December 2006 to April the formula for ellipsoid bodies (Griffith and Mylotte, 1987): 2007 at night (from 20:00 to 22:00) near a temporary pond (Fig. with L = prey length and W = prey width. If partially digested 2A) and a small stream (Fig. 2B) in a cocoa plantation (5 ha), body parts were retrieved, the regression formulae proposed which is located behind the campus of the Universidade Estadual by Hirai and Matsui (2001) were used to estimate the original de Santa Cruz (14°47’45’’S, 39°10’20’’W), municipality of prey size, followed by the volume calculation using the above Ilhéus, southern Bahia, Brazil. In the cacao plantations of mentioned formula. For regression analyses XLSTAT 2008 southern Bahia the shelter of trees of the original Atlantic (www.addinsoft.de) was used. To meet statistical assumptions rainforest vegetation is used to shade the cacao trees. This prey volume was log+1 transformed (Zar, 1999). ��The index of shading allows the plantation to conserve similar humidity relative importance (IRI) was applied as a measure that reduces indexes as the less impacted Atlantic forest patches. Faria et bias in description of animal dietary data. It was introduced al. (2007) found these plantations to harbor over 81% of the by ��Pianka, Oliphant and Iverson (1971)�� and Pianka (1973): amphibian diversity found in not anthropogenized forests. Frogs were captured and transferred to the nearby laboratory. IRIt ( PO t )( PI t PVt ) Snout-vent length (SVL; to nearest 0.1 mm) and mouth width (MW) were measured using a digital caliper. Body mass where POt is the percentage of occurrence (100 x number (BM; to nearest 0.1g) was recorded using a digital balance. of stomachs contained t item / total number of stomachs), Each frog’s stomach was flushed following the methodology PIt is the percentage of individuals (100 x total number of proposed by Solé et al. (2005) and specimens were released at individuals of t in all stomachs/total number of individuals of the capture site during the same night, about two to four hours all taxa in all stomachs), and PVt is the percentage of volume after having been captured. Stomach contents were transferred (100 x total volume of individuals of t in all stomachs/total Figure 1. Leptodactylus ocellatus, adult female. Diet of Leptodactylus ocellatus from Southern Bahia, Brazil 11 volume of all taxa in all stomachs). In order to compare summarized in Table 1. A total number of 77 stomachs the trophic niche breath the standardized Shannon-Weaver revealed at least one prey item and 38 stomachs were entropy index J was used (Weaver and Shannon, 1949): empty. The mean number of prey items per stomach H J was 7.52 ± 9.46 (min= 1; max= 44). Volume of prey log(n ) items ranged from 1.02 – 25481.11 mm3 (mean ± SD 3 whereby, 634.56 ± 2915.79 mm ). Most frequent prey items were Lepidoptera larvae (N= 304, N%= 53.52), H ¦ pilog(p i ) followed by Araneae (N= 39, N%= 6.87) and Diptera p is the relative abundance of each prey category, calculated i larvae (N= 35, N%= 6.16). Regarding the frequency as the proportion of prey items of a given category to the total of occurrence, Lepidoptera larvae, Araneae, and number of prey items (n) in all compared studies. To calculate Coleoptera were most important (each F= 21, F%= the trophic niche breadth, the Levins index (B) was used (Krebs, 3 1989): 27.27). Lepidoptera larvae (V= 113317.7 mm , V%= 3 1 63.15), Coleoptera (V= 16492.2 mm , V%= 9.19) and B 2 3 ¦ pi Hemiptera (V= 13291.3 mm , V%= 7.14) resulted to be the most important prey categories in terms of where p = fraction of items in the food category i; range = 1 to i volume. The index of relative importance showed that N. the diet of L. ocellatus was dominated by Lepidoptera larvae (IRI = 3182.07), followed by Coleoptera (IRI Results = 394.72) and Araneae (IRI= 276.53). S��imple linear A total of 117 frogs were captured including regression analyses revealed no significant relationships predominately adult and subadult specimens measuring between SVL or mouth width of L. ocellatus and from 32.01 mm to 142.29 mm SVL (mean ± SD 91.33 prey volume, minimum lengths of prey items and ± 15.05 mm; Fig. 3) and with a weight of 8.27–159.25 maximum length of prey items in our study (Fig. 4). g (mean ± SD 85.63 ± 31.35 g). Mouth width measured The Levins index observed in our samples was 8.51 13.99 to 38.52 mm (mean ± SD 30.60 ± 4.33 mm). and the standardized Shannon-Weaver index was 0.56. Data on the diet of L. ocellatus at the study area are Figure 2. Study site. Temporary pond (A) and small stream (B), where specimens of Leptodactylus ocellatus were collected. 12 Mirco Solé et al. Discussion (2003) found, respectively, one specimen of the anurans Our sample was biased toward adults, which were Hypsiboas albomarginatus, Leptodactylus ocellatus and frequently found on the margins of the temporary pond Physalaemus crombiei and one fish Poecilia( vivipara) and the small river in open areas as well as in denser ingested by specimens of L.

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