Lizards, Snakes, and Amphisbaenians from the Quaternary Sand Dunes of the Middle Rio Sao Francisco, Bahia, Brazil
1996; The Society for the Study of Amphibians and Reptiles; Volume: 30; Issue: 4 Linguagem: Inglês
10.2307/1565694
ISSN1937-2418
Autores Tópico(s)Species Distribution and Climate Change
ResumoA Quaternary sand dune area was discovered in the morphoclimatic domain of the semiarid Brazilian Caatinga. This site consists of high continental dunes located on both banks of the middle Rio Sao Francisco, Bahia, Brazil. The area contains a very unique fauna presenting striking adaptations to psammophily and high levels of species richness and endemism. A total of 6904 specimens comprising 36 lizard (including amphisbaenians) and 25 snake species were collected at the study sites. This area of approximately 5000 km2 includes 20 endemic reptiles and several newly described genera and species. This fauna is particularly characterized by an abundance and high diversity of fossorial and nocturnal forms differing strongly in ecological composition from Caatinga faunas and previously studied North American, Kalaharian, and Australian desert faunas. These differences may be a result of an association of an ecogeographic mechanism of speciation initially synchronic and latter replaced by a classic allopatric speciation which occurred in an ancestral Caatinga fauna. It is postulated that the last event of speciation possibly took place when the Sao Francisco river attained full exorrheism dividing formally continous sands and isolating ancestral psammophilic populations on opposite banks. At present, four closely related species pairs isolated by the river support this model. The last period of species differentiation most likely corresponded to the end of Wurm-Wisconsin glacial period. l erpetology, Vol. 30, No. 4, p. 513-523, 1996 996 Society for the Study of Amphibians and Reptiles a es, and Amphisbaenians from the Quaternary s of the iddle Rio SAo Francisco, Bahia, Brazil A major task for herpetologists in South America has been to identify faunal uniqueness and to work out taxonomic relationships necessary for interpretation of zoogeographic and evolutionary patterns. Relatively few studies on assemblages of squamates have been made for this region, most of them in forest areas (see Duellman, 1990 for a review). For Brazilian opencanopy scrublands, the only studies available are a comprehensive account on the reptiles of northeastern Brazil (Vanzolini et al., 1980), an ecological study on a snake assemblage in the caatinga (Vitt and Vangilder, 1983), two preliminary studies on the cerrado lizard communities (Vitt, 1991; Vitt and Caldwell, 1993), and a few studies of lizards in Amazonian savanna regions (Magnusson et al. 1985; Magnusson 1987, Magnusson and Silva, 1993; Vitt and Carvalho 1995). The present study began in 1980 with a survey of amphibians and reptiles in a semiarid and physionomically characteristic region of northeastern Brazil encompassing ca. 800,000 513 This content downloaded from 157.55.39.32 on Mon, 10 Oct 2016 04:23:58 UTC All use subject to http://about.jstor.org/terms MIGUEL TREFAUT RODRIGUES km2 locally known as Caatinga. Although the herpetological fauna of the caatinga is among the best known compared to that of other morphoclimatic domains of Brazil (i.e., Ab'Saber, 1977) previous work has been restricted to the core area (e.g., Vanzolini, 1974; Vanzolini et al. 1980). I describe a faunistically unknown desertlike area of caatinga adjacent to the banks of the Rio Sao Francisco in the state of Bahia. Preliminary work indicated that the area contained a very peculiar lizard fauna characterized by striking adaptations for psammophily in all species. After several expeditions to these sand dunes, the faunal survey of its reptiles still remains incomplete, but clearly species richness and endemism are unparalleled to those elsewhere in South America. In an area comprising roughly 5.000 km2 (Barreto, 1993), 36 species of lizards and amphisbaenians can be found, a local species richness greater than that of Amazonia and probably rivalled only by those in Australian deserts. In addition, 25 species of snakes are known to this area and the presently known endemic species of squamates reached a total of 20 (32% of the fauna). Although the area today cannot be adequately described as a desert, it was certainly one by the end of the Wiirm-Wisconsin glacial period (Tricart, 1974 Barreto, 1993); when at least some of the endemic species probably evolved. Some of the adaptations presented by its species, as psammophily and nocturnality, are similar to species typical of many deserts (e.g., Pianka, 1986). Following formal description of the majority of several new genera and species (Rodrigues, 1991a, b, c, d; 1993a, b; Vanzolini, 1991a, b), my main objective in this paper is to summarize the available information on the area and to bring this unique fauna to the attention of the herpetological community to facilitate future studies. In addition, it is possible that this rich sandy enclave in caatingas will become a useful model in testing recent hypothesis on desert lizard diversity developed after the studies of Pianka and collaborators in the Kalahari, North American, and Australian systems (Pianka, 1986). MATERIALS AND METHODS The study area is located at Rio Sao Francisco (approximately 9-11?S, 41-43?W) where the river flows across quaternary dunes (Fig. 1). Serra do Estreito is a large and linear quartzitic outcrop emerging from the alluvial plain of the river to a height of 600 m above sea level on the left bank. Situated between the Serra do Estreito and the river is a large field of sand dunes, hereafter referred as the Xique-Xique dune field. These white to yellowish eollic parabolic dunes are the largest found in South America and are formed by fine dystrophic sands. The sand dunes are variable in elevation (20-100 m) and held together by thickets of a thorny and xeromorphic vegetation. Dominant thickets are formed by the associations of Cactaceae (Opuntia and Cereus) and Bromeliaceae (Brome ia sp.), with scattered shrubs of Euphorbiaceae, Mirtaceae, Bombacaceae, Celastraceae, L guminosae, or Simaroubaceae. Some individuals of a thorny and low Olacaceae and Mirtaceae form isolated thickets. Large spaces of ba e sand intercalate the clumps of vegetation, below which a leaf litter mat is also present. Only rarely do some of the shrubs reach 5 m. The only perennial river flowing across this area is the Rio Icatu, a small tributary of Sao Francisco. Williams (1925), Rodrigues (1991a), Barreto (1993), Martins (1995), and Rocha (1995) provide additional information on this area. Study sites at Xique-Xique dune field were concentrated at Ibiraba and Queimadas, State of Bahia. The Casanova dune field was studied at Alagoado downstream on the north bank of the river (Fig. 1). Although the vegetation, soil, and general physiognomy are similar at the two sites, the relief is less accentuated with smaller and sometimes indistinct dunes at Alagoado. At the rig t margin of the river, field work was centered in Santo Inacio and Vacaria. Santo Inacio is a contact zone where the terminal northern portion of the large Serra do Espinhaco (locally Serra do Assurua) meets the alluvial plain of the Sao Francisco. The Serra do Assurua is a local mountain range with typical campos rupestres (an open type of vegetation characteristic of rocky substrates). Local habitats are a co plex mosaic of several vegetation types. There are large outcrops of quartzitic rocks and conglomerates separated by sand-gravel areas. Vegetation is also clumped in thickets where leaf litter is present. Some twisted cerrado trees (characterized by a thickened bark and leathery leaves reaching 4-10 m) and scattered individuals of Velloziaceae are also found. In the alluvial plain of the river at Lagoa the Itaparica are dunes identical to that of the opposite side. At Vacaria the vegetation is characteristic of the caatingas although the soils are sandy with low, thorny, and xeromorphic plant species. In all intervening areas typical caatinga with rocky soils occurs. The region is subject to the same general climatic regime despite its high levels of habitat heterogeneity. Annual precipitation reaches 700 mm but is characteristically irregular with rains concentrated from April to October. A dry season, characterized by the complete lack of rain, extends from November to March. Temperatures are relatively constant throughout the year (24 to 28 C) with absolute maxima near 40 C and minima close to 10 C
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