Feeding ecology of Marmosa demerarae (Thomas, 1905) and Marmosops bishopi (Pine, 1981) (Mammalia, Didelphidae) in forest fragments of the southern Amazon

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We assessed the relative diet composition and level of trophic niche overlap of two sympatric didelphids, Marmosa demerarae and Marmosops bishopi, through the evaluation of food items consumed in forest fragments of different sizes in the southern Amazon region. The stomach contents of 107 individuals (42 M. demerarae and 65 M. bishopi) were analyzed by volume and frequency. The degree of similarity between the diets of the two species was quantified using Pianka’s index. The relative importance of the different food items consumed was quantified with the Index of Alimentary Importance. Both species revealed flexibility in their feeding preferences but consumed predominantly coleopterans. Vegetable items were only identified in the diet of M. demerarae. Trophic niches of these species overlapped greatly (76%), suggesting strong competition for food items between them in the sampled fragments. Marmosa demerarae presented a broader trophic niche, consuming a greater variety of items than M. bishopi. Temporal changes in diet composition was attributed to fluctuations in the availability of food resources and to influence from the pasture matrices within these environments.


Ecologia alimentar de Marmosa demerarae (Thomas, 1905) e Marmosops bishopi (Pine, 1981) (Mammalia, Didelphidae) em fragmentos florestais no sul da Amazônia. Avaliamos a composição relativa da dieta e o nível de sobreposição de nichos de dois marsupiais simpátricos, Marmosa demerarae e Marmosops bishopi, através da avaliação de itens alimentares consumidos em fragmentos florestais de diferentes tamanhos na região sul da Amazônia. Nós analisamos o conteúdo estomacal de 107 indivíduos, 42 M. demerarae e 65 M. bishopi, de acordo com os métodos de taxa volumétrica e frequência. O grau de similaridade entre as dietas das duas espécies foi quantificado utilizando o índice de Pianka. A importância relativa dos diferentes itens alimentares consumidos foi estimada pelo Índice de Importância Alimentar. Ambas as espécies revelaram flexibilidade em suas preferências alimentares consumindo predominantemente coleópteros. Os itens vegetais foram identificados apenas em M. demerarae. A avaliação de itens alimentares mostrou sobreposição de 76% entre os nichos tróficos das duas espécies, sugerindo a existência de uma forte competição por itens alimentares entre eles nos fragmentos amostrados. Marmosa demerarae mostrou um nicho trófico mais amplo, consumindo uma maior variedade de itens em relação a M. bishopi. A alteração na composição das dietas foi atribuída a flutuações na disponibilidade de recursos alimentares e à influência das matrizes de pastagem nesses ambientes.

New records of Glironia venusta, Thomas, 1912 (Mammalia, Didelphidae), from the Amazon and Paraguay Basins, Brazil

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Glironia venusta is a rare and poorly known species of tropical South America. There are few records and museum specimens. Likewise, little is known about its ecology and distribution. For Brazil, previous records had been noted in the states of Amazonas, Rondônia and Pará, all within the Amazon basin. We report the capture of a young female in Rondônia and an adult male in southwest Mato Grosso state, both in Tomahawk-type traps on lianas ~1.5m above the ground. Specimens were deposited at the mammals collection of Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, with collection numbers 4577 and 5237. The latter specimen is the first ever recorded of this species in Mato Grosso and in the Paraguay River basin, and represents a distribution extension of more than 1000 km. Unfortunately, the forest fragment where this specimen was collected—surrounded by rural agricultural settlements—was burned shortly afterwards.


Nuevos registros de Glironia venusta, Thomas, 1912 (Mammalia, Didelphidae), para la cuenca amazónica de Brasil. Poco se conoce sobre la ecología y distribución de Glironia venusta, en apenas algunos registros y una decena de especímenes en colecciones. Para Brasil, se conocía solo de los estados de Amazonas, Rondonia y Pará, en la cuenca amazónica. Una hembra joven fue colectada en Rondonia y un macho adulto en el estado de Mato Grosso, ambos con trampas tipo Tomahawk colocadas en lianas, a aproximadamente 1.5 metros de altura. Ambos especímenes están depositados en la Colección de Mamíferos del Instituto Nacional de Investigaciones de la Amazonia (INPA) (números INPA 4577 y 5237). El ejemplar del suroeste de Mato Grosso es el primer registro para el estado y para la cuenca del alto río Paraguay, expandiendo más de 1000 kilómetros la distribución de la especie. El área de colecta fue quemada completamente poco después del registro y actualmente se encuentra rodeada de asentamientos rurales.

Efficiency of four trap types in sampling small mammals in forest fragments, Mato Grosso, Brazil

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We sampled the small mammal community inhabiting semi-deciduous forest fragments in Mato Grosso, Brazil, using 4 different types of traps, Tomahawk, Sherman, snap,
and pitfall, in order to evaluate the efficiency of different trap types in sampling efforts. During our study, we captured a total of 984 individuals of 27 species over 33800 trap nights. Sherman traps captured a significantly greater abundance of individuals and higher species richness than the other 3 types of traps. The Tomahawk and snap traps exhibited similar capture rates, in both the number of individuals and species captured. Pitfall traps captured the fewest numbers of individuals and species and were the only trap type to have different, although not significant, capture rates between seasons. Pitfall traps captured four times more individuals during the wet season than during the dry season. Despite their relative inefficiency and the large effort it takes to install pitfall traps, we found that these types of traps can be useful in augmenting trapping efforts, as they often capture species that do not, or rarely, fall into other types of traps.


La eficiencia de cuatro tipos de trampas en un relevamiento de micromamíferos en fragmentos de bosques en Mato Grosso, Brasil. Una comunidad de pequeños mamíferos fue estudiada en fragmentos de bosques semideciduos en el estado de Mato Grosso (Brasil) usando 4 tipos de trampas, de captura viva (Tomahawk y Sherman), de captura muerta (trampa de golpe: snap) y trampa de caída (pitfall). Considerando todos los tipos de trampas tuvimos un esfuerzo total de 33800 trampas/noche, habiendo capturado 984 individuos de 27 especies. Las trampas Sherman demostraron ser significativamente más eficientes que los otros tipos utilizados tanto para abundancia, como para riqueza de especies. Las trampas Tomahawk y snap demostraron tener eficiencias similares en número de individuos y en número de especies capturadas entre las áreas estudiadas. Cuando se comparó la eficiencia entre las dos estaciones del año, verano e invierno, solamente las pitfall capturaron más individuos durante la estación de invierno en relación al verano; a pesar de haber tenido casi cuatro veces más de capturas durante este período, los resultados no fueron significativos. Pese al gran esfuerzo para el montaje de las pitfall, es fundamental su uso como complemento de los muestreos, por ser este método capaz de capturar especies que difícilmente, o raramente, logran ser colectadas usando otros tipos de trampas.