ABSTRACT We describe the diversity, natural history and structure of snake assemblages from Marajó Island, state of Pará, Brazil, after analyzing 439 specimens deposited in herpetological collections. We tested the hypothesis that snake assemblages from forest and open areas of Marajó Island are distinct with regard to their structure, composition and functional groups. To compare the snake composition of the forest and open areas of Marajó with other comparable assemblages in Brazil, Principal Coordinate Analysis and Clustering tests were performed. A total of 61 species of snakes was recorded for Marajó, with ten species cited for the first time for the study area (Atractus natans Hoogmoed & Prudente, 2003, A. schach (Boie, 1827), Dendrophidion dendrophis (Schlegel, 1837), Helicops hagmanni Roux, 1910, Hydrops martii (Wagler in Spix, 1824), Lygophis meridionalis (Schenkel, 1901), Erythrolamprus typhlus (Linnaeus, 1758), Philodryas argentea (Daudin, 1803), Siphlophis cervinus (Laurenti, 1768), and Thamnodynastes sp.). The composition and structure of snake assemblages between forested and open were different, with five functional groups of snakes in forest areas, and three groups in open areas, based on habit and habitat. In all, 19 species were exclusive to forest areas, 10 were exclusive to open areas and 26 species were recorded in both areas. Our results revealed greater richness for forested areas, probably due to greater habitat heterogeneity. The species composition for forested area in Marajó was similar to that found in other Amazonian assemblages, while that for open areas was more similar to the Pantanal region than other open area assemblages. The general structure of the snake assemblage of Marajó was dominated by anurophagous, terrestrial and diurnal species. Terrestrial, arboreal and semi-arboreal snakes showed a seasonal offspring production pattern, while the pattern for aquatic and semi-aquatic species was aseasonal. The structure of assemblages was influenced by both historical and ecological factors.

Um inventário estruturado de serpentes foi realizado na Base Operacional Geólogo Pedro de Moura (BOGPM), localizada na Bacia Petrolífera de Urucu, Município de Coari, Amazonas, nos anos de 2003, 2004 e 2007. Nas quatro expedições realizadas (51 dias de coleta) foram registradas 47 espécies de serpentes, pertencentes a sete famílias e 33 gêneros. Foram utilizados quatro métodos complementares de amostragem de serpentes: armadilha de interceptação e queda, encontros ocasionais, procura limitada por tempo a pé e procura limitada por tempo de carro. Das 47 espécies coletadas, Liophis reginae (n= 14), Philodryas viridissima (n= 9), Philodryas boulengeri (n= 7) e Oxybelis fulgidus (n= 7) foram as mais abundantes em toda região. O maior número de espécies e espécimes foi registrado pela procura limitada por tempo de carro (52,8%). Estudos anteriores indicam que as localidades ao sul do Rio Amazonas (como região Leste do Pará, Usina Hidrelétrica de Tucuruí, Estado do Pará, e de Samuel, Estado de Rondônia) apresentam maior riqueza quando comparadas às regiões ao norte do Amazonas (como Município de Manaus, Reserva do INPA-WWF e Usina Hidrelétrica de Balbina, Estado do Amazonas). Desta forma, é possível inferir que o levantamento das serpentes da região de Urucu ainda não esteja completo, sendo necessário um maior esforço de coleta para que novos registros sejam adicionados para a área.

A structured snake inventory was carried out at the Base Operacional Geólogo Pedro de Moura (BOGPM), located at the Urucu Petrol Basin, Municipality of Coari, Amazonas, during 2003, 2004 and 2007. Throughout four sampling expeditions (51 collection days), seven species of snakes, belonging to seven families and 33 genera, were recorded. Four complementary sampling methods were used: pitfall traps with drift fence, occasional encounters, time-limited search on foot and time-limited search by car. Of the 47 collected species Liophis reginae (n= 14), Philodryas viridissima (n= 9), Philodryas boulengeri (n= 7) and Oxybelis fulgidus (n= 7) were the most abundant in the region. The highest number of species and specimens was obtained by the time-limited search by car (n=52.8%). Previous studies indicate that localities south of the Amazonas river (such as the eastern region of Pará and Tucuruí, state of Para, and Samuel Hydroelectric Plants, state of Rondônia) present a greater richness when compared to those north of the Amazonas river (such as the mucipality of Manaus, INPA-WWF Reserve and Balbina Hydroelectric Plant, state of Amazonas).Thus, it is possible to infer that the snake inventory in Urucu region is not yet complete, requiring more sampling efforts so that new records can be obtained for the area.