ABSTRACT
Abstract In this article, by using carbon stable isotopes, we assessed the past and present land use influences that riparian areas are subject within agricultural landscapes. Emphasis is given to the understanding of the effects of the 2012 Brazilian Forest Act on such areas. We selected five riparian areas within a highly C4 dominated agricultural landscape. Three of them had 30 meters native riparian forest buffer (NRFB) and two of them had 8 meter and no NRFB. We used three 100 meter-transects located 5, 15 and 30 meters relative to stream channel to obtain soil samples (0 - 10 cm). All riparian areas presented soil carbon isotopic signatures that are not C3 (native forests) irrespective of having or not 30 meters NRFB. Two cases presenting less than 30 meters NRFB had higher C4 derived carbon contribution. All of the other three areas that followed the 30 meters NRFB presented, to some degree, C4 derived carbon, which was attributed to C4 organic matter deposition originated from cultivated areas and, in one case, to the persistence of former exotic grasses. With the 2012 Forest Act allowing narrower buffers (< 30 meters), we expect C4 contributions to soil organic matter to remain high in riparian areas and streams within agricultural landscapes dominated by C4 plants where 30 meter NRFB is no longer required. Such contributions will likely continue to have detrimental effects on stream water quality and biota.
Resumo Neste artigo, ao utilizar isótopos estáveis de carbono, nós avaliamos as influências presentes e pretéritas do uso da terra a que as áreas ripárias estão sujeitas quando situadas dentro de paisagens agrícolas. Ênfase é dada ao entendimento dos efeitos do Código Florestal de 2012 em tais áreas. Nós selecionamos cinco áreas ripárias em uma paisagem agrícola altamente dominada por plantas C4. Três delas apresentam faixa ripária de floresta nativa (FRFN) de 30 metros de largura e as outras duas apresentam FRFN de 8 e 0 m (i.e. sem FRFN). Nós utilizamos três transectos de 100 metros localizados a 5, 15 e 30 metros de distância do canal fluvial para obter amostras de solo (0 - 10 cm). Todas as áreas ripárias apresentaram assinaturas isotópicas do carbono do solo que não são C3 (floresta nativa) independentemente de apresentarem ou não FRFN de 30 metros. Os dois casos em que FRFN era menor que 30 m apresentaram maior contribuição de carbono oriundo de plantas C4. Todas as outras três áreas com FRFN de 30 m também apresentaram, em algum grau, carbono oriundo de plantas C4. Todas as outras três áreas com FRFN de 30 m também apresentaram, em algum grau, carbono oriundo de plantas C4 que foi atribuído è deposição de matéria orgânica de plantas C4 originada das áreas cultivadas e, em um caso, è persistência de gramíneas exóticas pré-existentes. Com o Código Florestal de 2012 permitindo FRFN mais estreitas (< 30 metros), nós esperamos que a contribuição de plantas C4 para a matéria orgânica permaneça alta em áreas ripárias e rios dentro de paisagens agrícolas dominadas por plantas C4 onde a FRFN de 30 m não é mais uma obrigação. Tais contribuições irão, provavelmente, continuar a ter efeitos prejudiciais è qualidade de água dos rios e à sua biota.
ABSTRACT
Background Environmental devastation threatens the survival of many species, including venomous snakes such as the South American rattlesnake Crotalus durissus terrificus. This observation is based on the decrease of snakes collected and donated to Brazilian research institutes. Nevertheless, some individuals have managed to survive and procreate. The question is how these snakes are adapting in these new environmental conditions.Methods To answer it, the carbon-13 level of rattlesnakes and their feed (either laboratory or wild mice) was evaluated by isotope-ratio mass spectrometry. Thus, rattle segments from 16 adults and 15 offspring of captive snakes, and of three wild newborn C. d. terrificus were evaluated as well as 17 Mus musculus mice captured in traps, four live feeder mice and the ration offered to mice at animal houses.Results The isotopic exchange time of the captive adult snakes (n = 16) varied between 33 and 37 months and of captive-born animals (n = 15), until reaching a plateau of equilibrium, varied from 18 to 24 months. Regarding the captured Mus musculus (n = 17), 88.23% (n = 15) were from a C4 environment. Of the six rattle rings from offspring of captured C. d. terrificus, five were from a C4environment, whereas of the 170 rattle rings studied, 60% originated from a C3 environment and 40% from a C4. The same carbon-13 values were found in captive snakes.Conclusions Based on the present results, it can be inferred that most C. d. terrificus snakes (60%) fed animals from a C3environment; birds consist of an alimentary alternative for snakes, as well as rodents, small reptiles and amphibians; different venom compositions among snakes from the same region may be related to the food type; the primary rattle of offspring reflects the maternal diet during gestation; and, finally, the different rattle rings indicate the alimentary history of these animals.(AU)
Subject(s)
Crotalus/anatomy & histology , History , IsotopesABSTRACT
Background Environmental devastation threatens the survival of many species, including venomous snakes such as the South American rattlesnake Crotalus durissus terrificus. This observation is based on the decrease of snakes collected and donated to Brazilian research institutes. Nevertheless, some individuals have managed to survive and procreate. The question is how these snakes are adapting in these new environmental conditions.Methods To answer it, the carbon-13 level of rattlesnakes and their feed (either laboratory or wild mice) was evaluated by isotope-ratio mass spectrometry. Thus, rattle segments from 16 adults and 15 offspring of captive snakes, and of three wild newborn C. d. terrificus were evaluated as well as 17 Mus musculus mice captured in traps, four live feeder mice and the ration offered to mice at animal houses.Results The isotopic exchange time of the captive adult snakes (n = 16) varied between 33 and 37 months and of captive-born animals (n = 15), until reaching a plateau of equilibrium, varied from 18 to 24 months. Regarding the captured Mus musculus (n = 17), 88.23% (n = 15) were from a C4 environment. Of the six rattle rings from offspring of captured C. d. terrificus, five were from a C4environment, whereas of the 170 rattle rings studied, 60% originated from a C3 environment and 40% from a C4. The same carbon-13 values were found in captive snakes.Conclusions Based on the present results, it can be inferred that most C. d. terrificus snakes (60%) fed animals from a C3environment; birds consist of an alimentary alternative for snakes, as well as rodents, small reptiles and amphibians; different venom compositions among snakes from the same region may be related to the food type; the primary rattle of offspring reflects the maternal diet during gestation; and, finally, the different rattle rings indicate the alimentary history of these animals.