Water Balance and Spatial Distribution of an Anuran Community from Brazil

Abstract

Terrestrial amphibians may dehydrate when exposed to low humidity, representing an important factor affecting spatial distribution and community composition. In this study we investigated whether rates of dehydration and rehydration are able to explain the spatial distribution of an anuran community in a Restinga environment at the northern coast of the State of Bahia, Brazil, represented by 11 species distributed in 27 sample units. The environmental data set containing 20 variables was reduced to a few synthetic axes by principal component analysis (PCA). Physiological variables measured were rates of dehydration, rehydration from water, and rehydration from a neutral substrate. Multiple regression analyses were used to test the null hypothesis of no association between the environmental data set (synthetic axes of PCA) and each axis representative of a physiological variable, which was rejected (P , 0.001). Of 15 possible partial regressions only rehydration rate from neutral substrate vs. PC1 and PC2, rehydration rate from water vs. PC1, and dehydration rate vs. PC2 were significant. Our analysis was influenced by a gradient between two different groups of sample units: a beach area with high density of bromeliads and an environment without bodies of water with low density of bromeliads. Species of very specific natural history and morphological characters occur in these environments: Phyllodytes melanomystax and Scinax auratus, species frequently occurring in terrestrial bromeliads, and Ischnocnema paulodutrai, common along the northern coast of Bahia and usually found in forest remnants within environments with low number of bodies of water. In dry environments species with lower rates of dehydration were dominant, whereas species showing greater rates of dehydration were found predominantly in microhabitats with greater moisture or abundance of bodies of water.

Composition and diversity of anurans in the Restinga of the Conde municipality, northern coast of the state of Bahia, northeastern Brazil

“…Furthermore, some SUs in shrubby vegetation zones had terrestrial tank bromeliads (Figure 2A), plants that retain moisture between their leaves and accumulate water inside the leaf-tank (Freitas et al 2000, Cogliatti-Carvalho 2001. In shrubby vegetation zones, terrestrial tank bromeliads are the only source of water supply to maintain the minimum physiological needs of anurans (Dabés et al 2012) and are considered fundamental ecological units in the Restinga ecosystem since they are used by many wildlife groups for shelter and/or as breeding sites (Peixoto 1995, Richardson 1999, Carvalho-e-Silva et al 2000, Schneider & Teixeira 2001, Teixeira et al 2002. The phytotelm-dweller hylids Phyllodytes melanomystax and Trachycephalus atlas were exclusively observed in these bromeliads, although as singletons.…”

“…This mode of reproduction allows this species to breed in environments deprived of water bodies (Xavier & Napoli 2011). Furthermore, P. paulodutrai has a low dehydration rate and high rate of rehydration from a neutral substrate (Dabés et al 2012), which helps to explain its ability to occupy different types of environments, including those under high osmotic stress, as is the case of shrubby vegetation zones.…”

“…Napoli, unpublished data). This is also the case for the amphibian fauna, for which studies are concentrated in its southern portion and emphasizing forest patches in the Mata de São João municipality (e.g., Juncá 2006, Bastazini et al 2007, Dabés et al 2012. Indeed, the amphibians of the northern limit of the NC are represented in herpetological collections mainly by specimens obtained from sporadic and occasional inventories, which points to the urgency in the development of faunistic and ecologic studies for the region.…”

Effects of variations of osmolarity on behavior in Leptodactylus macrosternum Miranda-Ribeiro, 1926 (Leptodactylidae, Anura, Amphibia)

“…Species which do not present either physiological or morphological adaptations, to cope with water loss by evapotranspiration, may use behavioral responses as an important mechanism to resist dehydration (Wells, 2007). Among the many water saving behavioral aspects, the following stand out (Stille, 1958): 1) activity period, which is mostly nocturnal for anurans; avoiding high temperatures and low humidity during the day; 2) spatial distribution through habitat and micro-habitat choice, because amphibians that are less tolerant to dehydration are found mostly in regions with elevated humidity or near water bodies (Pough et al, 1977;Bastazini et al, 2007;Xavier and Napoli, 2011;Dabés et al, 2012); 3) aggregation of newly metamorphosed individuals on salamander adults; reducing the exposed surface area when under water stress (Rohr et al, 2002); 4) fossorial habit -occupying holes in the ground dug by other animals or by the amphibians themselves (Shoemaker and Nagy, 1977;Toledo and Jared, 1993;Warburg, 1997;Cartledge et al, 2006;Wells, 2007).…”

“…Most studies on water balance and behavior use anurans from temperate climates, and neotropical anurans may possess specific adaptations (Navas et al, 2004;Dabés et al, 2012). This study focuses on Leptodactylus macrosternum, a semi-aquatic frog found in the tropical region of South America, which like most species of genus Leptodactylus can be found in terrestrial habitats, but needs open water to reproduce (Heyer, 1969), (Heyer and Giaretta, 2009).…”