Orientador: Ivan Sazima

Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia

Resumo: Uma taxocenose de serpentes de mata foi estudada na região de Manaus entre 1991 e 1994. O método consistiu de procura visual "limitada por tempo" e ocasional, resultando em 685 encontros de serpentes. A taxa média de encontro foi de 0,064 e 0,217 serpente por hora-homem, durante o dia e à...

Resumo: Uma taxocenose de serpentes de mata foi estudada na região de Manaus entre 1991 e 1994. O método consistiu de procura visual "limitada por tempo" e ocasional, resultando em 685 encontros de serpentes. A taxa média de encontro foi de 0,064 e 0,217 serpente por hora-homem, durante o dia e à noite, na procura limitada por tempo. As espécies mais encontradas foram: Xelloxybelis argenteus, Bothrops atrox, lnzantodes cenchoa e Dipsas sp. O número de serpentes encontradas foi proporcional à quantidade de chuvas. A distribuição de comprimentos dentro das grandes linhagens de colubrídeos mostrou que fatores históricos são responsáveis pela distribuição geral de comprimentos na taxocenose. As relações entre comprimento da cauda e comprimento rostro-anal e entre este e peso mostrou forte relação entre tamanho de cauda e forma com os padrões de utilização de substrato. Os padrões de utilização do ambiente e horário de atividade encontrados na Reserva Ducke e em outras localidades da Amazônia indicam que "trocas" de espécies que utilizam diferentes substratos, dentro de uma mesma linhagem de colubrídeos, explicam grande parte das diferenças encontradas. As presas mais utilizadas foram lagartos, anuros, mamíferos, aves e serpentes, refletindo a influência de fatores históricos. As 50 espécies foram agrupadas em guildas com grande sobreposição em forma, tamanho e utilização de recursos. Os resultados sobre reprodução indicam tendência à sazonalidade para a taxocenose. A maioria dos padrões encontrados pode ser explica da por fatores históricos. É sugerido que a convivência de 50 espécies sintópicas de serpentes se deve principalmente à abundância de recursos e/ou às densidades baixas de serpentes

Abstract: Morphological analyses were based in three measurements: body length, tail length, and weight. An analysis of maximum length distribution within the major colubrid lineages (colubrines, South American xenodontines, and Central American xenodontines), that occur at RFAD, showed that...

Abstract: Morphological analyses were based in three measurements: body length, tail length, and weight. An analysis of maximum length distribution within the major colubrid lineages (colubrines, South American xenodontines, and Central American xenodontines), that occur at RFAD, showed that features related to these lineages (thus, historical) are responsible for most of the general pattern observed for colubrids and for the entire assemblage. The relationship between body and tail length showed that, in general, arboreal species have longer tails than terrestrials, that have longer tails than fossorials, in agreement with the idea that there is a strong effect of habitat use on tail length in snakes. Finally, an analysis of weight-length relationships showed that, in general, arboreals tend to be ligbter than terrestrials, that tend to be lighter than aquatics, confirming the effects of habitat use in snake body form. These tendencies became more evident in the analyses where colubrids were separated in major lineages. An additional analysis on color and color patterns confirmed the effect of defence in snake color patterns. A cluster analysis based on data on habitat use, time of activity, diet, and size (length and weight) split the assemblage into guilds where high overlaps in form and resource use are evident; in several cases these guilds were made of closely related species, indicating the presence of constraints inherent to each lineage sampled. Although data on reproduction is scarce for most species, there are snakes at Reserva Ducke in which births occur on1y during the rainy season and in others occur throughout the year. A general analysis of the presence of juveniles in the populations sampled indicated a strong tendency to seasonal breeding by the snakes of Reserva Ducke, contradicting most speculations on the patterns of juvenile recruitment in Amazonian snakes. The seasonality in reproduction, as in activity, may be related to the probably low availability of certain prey types during the dry season. A general analysis of the results indicate that most patterns found at Reserva Ducke may well be explained by historical factors as previously predicted by J. E. Cadle and H. W. Greene in a review of the role of history on the organization of neotropical snake assemblages. Concomitantly, a critical review of the arguments favoring the hypothesis that consider competition as a major structuring force in amazonian snake assemblages indicate that these arguments tend to be irrelevant before several evidences are found in natural assemblages, especially alterations in the reproductive success in the species thought to be competing. In conclusion, it is suggested, based on a series of arguments, that the co-occurrence os 50 snake species at Reserva Ducke may be due to the combination of the following: (1) resource abundance and/or low snake densities would allow the coexistence of a relatively large number of snake species; (2) thus, the populations would be regulated main1y by predation and/or other biotic and abiotic factors to a level where densities were not high enough to result in resource deployment (and, perhaps, competition) (some studies on Amazonian snake assemblages converged to these speculations while others, to completely conflicting ones). Concomitantly, the patterns found in the assemblage of Reserva Ducke may be a natural result of the history of colonization of the region by the various snake lineages that constitute this assemblage