Dietary Resource Use by an Assemblage of Terrestrial Frogs from the Brazilian Cerrado
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NORTH-WESTERN JOURNAL OF ZOOLOGY 15 (2): 135-146 ©NWJZ, Oradea, Romania, 2019 Article No.: e181502 http://biozoojournals.ro/nwjz/index.html Dietary resource use by an assemblage of terrestrial frogs from the Brazilian Cerrado Thiago MARQUES-PINTO1,*, André Felipe BARRETO-LIMA1,2,3 and Reuber Albuquerque BRANDÃO1 1. Laboratório de Fauna e Unidades de Conservação, Departamento de Engenharia Florestal, Universidade de Brasília, Brasília – DF, Brazil. 70.910-900, [email protected] 2. Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Campus Darcy Ribeiro, Brasília – DF, Brazil. 70.910-900, [email protected] 3. Programa de Pós-Graduação em Ecologia, Instituto de Ciências Biológicas, Universidade de Brasília, Campus Darcy Ribeiro, Brasília – DF, Brazil. 70.910-900. *Corresponding author, T. Marques-Pinto, E-mail: [email protected] Received: 08. June 2016 / Accepted: 07. April 2018 / Available online: 19. April 2018 / Printed: December 2019 Abstract. Diet is an important aspect of the ecological niche, and assemblages are often structured based on the ways food resources are partitioned among coexisting species. However, few works investigated the use of food resources in anuran communities in the Brazilian Cerrado biome. Thereby, we studied the feeding ecology of an anuran assembly composed of six terrestrial frog species in a Cerrado protected area. Our main purpose was to detect if there was a structure in the assemblage based on the species’ diet, in terms of the feeding niche overlap and the species’ size. All specimens were collected by pitfall traps placed along a lagoon margin, during the rainy season. We collected six frog species: Elachistocleis cesarii (172 individuals), Leptodactylus fuscus (10), L. furnarius (17), L. latrans (21), Physalaemus centralis (297) and P. cuvieri (112). The prey length and volume were related, to some extent, to the species morphology, except for E. cesarii. The observed niche overlap was greater than expected by chance. The prey type abundance and frog morphology had no relationships. Morphometric differences among frog species did not determine differences on the resource use, and the anuran assemblage fed on similar diet items, with a high dietary niche overlap. Keywords: anuran diet, Cerrado anurans, assemblage, feeding ecology, niche overlap. Introduction Anurans use mainly arthropods on diet (Toft 1980), but each prey type has a different importance for each species (Leite- Interspecific competition theories (Huisman & Weissing Filho et al. 2017). Several studies showed relationship be- 1999, Chesson 2000, Rees et al. 2001) or neutral theories (Bell tween the frog body size and prey size, suggesting that their 2001, Hubbell 2001) have been used to interpret the dynam- different use may benefit resource sharing among species ics and the structure of natural communities (Ernst & Rodel (Toft 1995; Lima & Moreira 1993, Vitt & Caldwell 1994, 2006). Communities can be integrated with structured as- Caldwell 1996). In a broad sense, specialist frog species eat semblages that evolved as units (Clements 1916, Pianka smaller and more prey (e.g. ants) than non-specialist or gen- 1973, Roughgarden 1976), resulting of species’ responses to eralist species (Caldwell 1996, Vitt and Zani 1996), suggest- environment constraints (Gleason 1926, Rotenberry & Wiens ing that some guilds can show smaller competition among 1980, Wiens & Rotenberry 1981, Homes et al. 1986, Eterovick species than expected by chance. et al. 2010) coupled (or not) to historical processes (França et Most studies on tropical anuran assemblages focused on al. 2008, Carnaval et al. 2009). In resource-rich environments, aspects of resource partition by means of the niche breadth it is not expected species competing, but when the resources and overlapping (Crump 1974, Inger & Colwell 1977, Du- are scarce, the competition tends to be strong. However, the ellman 1978, Toft 1982, Inger et al. 1987, Lima & Magnusson competition within the community can be reduced by the 1998, Protázio et al. 2015, Leite-Filho et al. 2017) or the occur- predation (Azevedo-Ramos et al. 1999, Hero et al. 2001), rence patterns and habitat use (Gascon 1991, Parris & Mac- habitat and resource heterogeneity, or by environmental Carthy 1999, Neckel-Oliveira et al. 2000, Parris 2004, Et- changes (Ernst & Rodel 2006). Thereby, the competition is a erovick & Sazima 2000). As the diet is a fundamental aspect key factor to be considered in studies that focus on niche re- of ecological niche, it seems reasonable that the community lationship among species (Brown & Lieberman 1973, Pianka structure reflects the way that food resources are shared 1973, Vitt & Carvalho 1995, Caldwell & Vitt 1999). If any among coexisting species (Andrew & Christensen 2001). structure is observed, it is often attributed to the competition On the other hand, pairs of closed related species using (Ernst & Rodel 2006). the same microhabitats showed a higher niche overlap (in Neotropical sites harbour the largest anuran diversity in the diet), and a null model analysis showed a lack of struc- the world (Bertoluci 1998, Heyer et al. 1990, Duellman 1999, ture in the spatial and acoustic niches, indicating the lack of Fouquet et al. 2006, Valdujo et al. 2012), exhibiting coexis- competition (Protázio et al. 2015a). Thus, the competition did tence of several species mediated by ecological interactions, not appear to regulate anuran assemblages, even when the phylogenetic history and environmental constraints (Fou- closely related species had a higher degree of morphological quet et al. 2006, Carnaval et al 2009, Protázio et al. 2015, Le- similarity, suggesting a conservative feature for the body ite-Filho et al. 2017). In anuran assemblages, as in other taxa, shape (Protázio et al. 2015b). In a comparison of pastures the diet is a dimension of the ecologic niche that can be parti- versus forests, the availability of mesic habitats and other tioned by species (Lima & Magnusson 1998) and may be af- landscape features explained a significant amount of varia- fected by ecological processes (Leite-Filho et al. 2017). Many tion in the community structure (Manenti et al. 2013), sug- anuran species take prey in a different proportion from the gesting that the resource distribution over the landscape can leaf litter, suggesting that they select their prey or possess explain the frog distribution and the community structure specialization for certain food items (Lima & Moreira 1993). (Oliveira et al. 2017). 136 T. Marques-Pinto et al. The Cerrado is a global conservation hotspot (Myers et al 2000), being the biggest, richer, and, possibly, more threat- ened savanna in the world (Oliveira & Marquis 2002, Silva & Bates 2002). Despite that Cerrado harbours a very diverse (Valdujo et al. 2012) and highly threatened amphibia fauna (Ribeiro et al. 2017), most of diet studies performed with frogs in the biome were focused in autoecological aspects (e.g. Brandão et al 2003, Biavati et al. 2004, Magalhães et al. 2016), and the effect of the food use by different species on community structure was not investigated. Herein, we evaluated the diet of six terrestrial frogs, focusing on their trophic relationships and the effect of their diet in the as- semblage structure, based on the niche overlapping, the rela- tive importance of prey for the species, and the frogs’ mor- Figure 1. Location of Águas Emendadas Ecological Station (ESECAE), phology on the size and volume of the consumed prey. In and Bonita Lagoon, in Federal District of Brazil. addition, we asked: 1) if frog species differ in their diets in terms of the prey type and abundance; 2) if the observed mm). Stomachs were extracted, and their items were counted, meas- niche overlap is different from the overlap expected by ured and identified to the order and/or family level (for Formicidae) chance; and 3) if the frogs’ body size and head size deter- under a stereoscopic microscope. For Isoptera, we counted different mine the size and volume of the consumed prey. castes (reproductive winged individuals, workers and soldiers) due to differences in distribution of these castes in the habitat (i.e. differ- ences in its availability). Material and Methods Statistical analysis Study site Prey volumes were estimated by using an ellipsoid formula (Biavati The study was carried out in a 10,500ha reserve named Estação et al. 2004): Ecológica de Águas Emendadas (Fig. 1), located in Planaltina municipal- V= 4/3 * π * w2/4 * l/2, ity, Distrito Federal, Brazil. (Marinho-Filho et al.1998). Vegetation is where w is the prey width and l is the prey length. The fre- typical for the Cerrado biome, including the cerrado sensu stricto, quency, numeric and volumetric percentage of each prey category open cerrado, ‘campo sujo’ (open fields, with scattered trees and were also calculated. To determine the relative importance index bushes), ‘veredas’ (wet fields with buriti [Mauritia flexuosa] palms) (Biavati et al. 2004) of each prey category in the diet, we used the fol- and open fields. The climate is tropical Aw in Koppen classification lowing formula: (Ribeiro & Water 1998), with a dry and cold season in the winter RII = (F% + N% + V%)/ 3, (from March to September), and a rainy and warm season in the where F% is the occurrence percentage, N% is the numeric per- summer (from October to February) (Ribeiro & Marinho-Filho 2005). centage, and V% is the volumetric percentage. Prey categories im- Samples were taken in Lagoa Bonita (15o35’22’’S; 47o41’49’’W, 960m portance values to the total stomach sample for each species were a.s.l.), a natural lagoon with margins covered by open fields and taken. We calculated the niche breadth for each species for abun- bush fields. dance items’ data by using the Simpson’s Index (Simpson 1949): B= 1 / ∑ni=1 pi2, Sample Methods where i is the resource category, p is the resource i category pro- All specimens were collected with 20 pitfall traps (iron buckets; 20L) portion, n is the total number of categories.