Cornfield effects on breeding and abundance of Oligoryzomys nigripes (Rodentia: Sigmodontinae)

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Small rodents rely on resource gathering during the breeding season to support their reproductive output and offspring survival. Since croplands may provide complementary food sources, we evaluated the influence of the presence of cornfield on the forest edge in Oligoryzomys nigripes (Olfers, 1818) abundance and breeding. We found that abundance, proportion of reproductive females and males, as well as the number of juveniles were higher in the cornfield-forest edges, with no seasonality, a pattern divergent from the seasonal reproduction described for the species. Therefore, our results supported the hypothesis of cornfields benefiting O. nigripes abundance and breeding success.


Efeitos do milharal na reprodução e abundância de Oligoryzomys nigripes (Rodentia: Sigmodontinae). Pequenos roedores dependem da aquisição de recursos para sustentar a reprodução e a sobrevivência da ninhada. Uma vez que plantações podem servir como fonte complementar de alimento, nós avaliamos a influência da presença de plantações de milho na borda da floresta sobre a abundância e a reprodução de Oligoryzomys nigripes (Olfers, 1818). Constatamos que a abundância, a proporção de indivíduos reprodutivos, assim como o número de juvenis foram maiores nas bordas dos campos de milharal, sem sazonalidade, um padrão divergente da reprodução sazonal descrita para a espécie. Nossos resultados suportam a hipótese de que as plantações de milho beneficiam a abundância e a atividade reprodutiva de O. nigripes.

Richness, endemism and conservation of sigmodontine rodents in Argentina

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Sigmodontine rodents, with 86 genera and ~430 living species, constitute one of the most successful radiations of Neotropical mammals. In this contribution, we studied the distributional ranges of 108 sigmodontine species in Argentina. Our objectives were (i) to establish geographical patterns of species richness and endemism, and (ii) to evaluate the regional conservation status of these taxa. We constructed a minimum convex polygon for each species, using information from literature and biological collections. Individual maps were superimposed on a map of Argentina divided into cells of 25 km on each side. For each cell, we calculated the species richness, which varied between 1 and 21 species, and its degree of endemism, which fluctuated between 0.001 and 3.28. There were 30 species of sigmodontine rodents distributed almost exclusively in Argentina, most of them restricted to forested areas (Southern Andean Yungas) or to arid and semiarid environments (High and Low Monte and Patagonian Steppe). Areas with high species richness and endemism scores corresponded grossly with the Southern Andean Yungas, the Humid Chaco plus the Paraná flooded savannas, the Alto Paraná Atlantic forests plus the Araucaria moist forests, the High Monte and the ecotone between the Patagonian steppe and the Valdivian temperate forests. A reassessment of the conservation status of sigmodontine rodents distributed in Argentina retrieved 2 extinct species, 7 endangered, 7 vulnerable, 6 near threatened and 13 data deficient. These numbers suggest a much more serious situation than the expressed by previous evaluations, highlighting the urgent need to establish conservation measures for the protection of this group.


Riqueza, endemismo y conservación de roedores sigmodontinos en Argentina. Los roedores sigmodontinos, con 86 géneros y ~430 especies vivientes, constituyen una de las radiaciones más exitosas de mamíferos neotropicales. En esta contribución estudiamos los rangos de distribución de 108 especies de sigmodontinos en Argentina. Nuestros objetivos fueron (i) establecer patrones geográficos de riqueza de especies y endemismo y (ii) evaluar el estado de conservación regional de estos taxones. Construimos un polígono convexo mínimo para cada especie, utilizando información de la literatura y colecciones biológicas. Los mapas individuales fueron superpuestos en un mapa de Argentina dividido en celdas de 25 km de lado. Para cada celda calculamos la riqueza de especies, que varió entre 1 y 21, y su grado de endemismo, que fluctuó entre 0.001 y 3.28. Hubo 30 especies de roedores sigmodontinos distribuidos casi exclusivamente en Argentina, la mayoría de ellos restringidos a áreas boscosas (Yungas andinas del sur) o a ambientes áridos y semiáridos (Monte alto y bajo y Estepa Patagónica). Las áreas con mayor riqueza de especies y valores más altos de endemismo se correspondieron groseramente con las Yungas andinas del sur, el Chaco húmedo más las Sabanas inundadas de Paraná, el Bosque Atlántico del Alto Paraná más los Bosques húmedos de araucaria, el Monte alto y el ecotono entre la Estepa Patagónica y los Bosques templados valdivianos. Una reevaluación del estado de conservación de los roedores sigmodontinos distribuidos en Argentina recuperó 2 especies extintas, 7 en peligro, 7 vulnerables, 6 casi amenazadas y 13 con datos deficientes. Estas cifras sugieren una situación mucho más grave que la expresada en evaluaciones anteriores, destacando la necesidad urgente de establecer medidas de conservación para la protección de este grupo.

Análise tricológica de pelos-guarda de roedores do pampa brasileiro, com uma chave de identificação

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A identificação de espécies por meio da tricologia é uma ferramenta simples, rápida e de baixo custo que pode ser aplicada em distintos campos. Nesse trabalho, analisamos os pelos-guarda de 17 espécies de roedores autóctones do pampa brasileiro e três espécies alóctones. De forma a facilitar a identificação de roedores com base no padrão dos pelos apresentamos uma chave dicotômica de identificação. Encontramos seis padrões principais de medula e três diferentes padrões de cutícula, com algumas características específicas importantes no reconhecimento dos táxons. Nesse trabalho são apresentadas as primeiras informações sobre os padrões tricológicos para seis espécies, além da complementação de informações para os demais táxons. Com isso, complementamos lacunas existentes em estudos tricológicos para pequenos mamíferos não voadores do Pampa brasileiro, distinguindo com sucesso a maioria das espécies e aumentando assim o conhecimento deste grupo no extremo sul do Brasil.


Trichological analysis of guard-hairs of rodents from Brazilian Pampa, with an identification key. Species identification using trichology is simple, cheap and fast, and can be used in various fields of study. We analyzed guard-hairs from 17 autochthonous rodent species and three other allochthonous species of the Brazilian Pampas. To aid rodent identification based on hair morphology, we provide an identification key, based on characteristics of the medulla and cuticle. We found six major medullar patterns, and three major cuticular patterns. Together, these provide characters useful for species-level identification. This article presents the first information on hair morphology of six rodent species, and complements existing data for others. Thus, we fill some gaps in the knowledge of the trichology of small non-volant mammals of the Brazilian Pampas, and distinguish most of species occurring in this southernmost region of Brazil.

Localidades típicas de micromamíferos en Patagonia: el viaje de Hatcher a la meseta del lago Buenos Aires, Santa Cruz, Argentina

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En base a la reconstrucción del viaje efectuado en 1898 por J.B. Hatcher y E.A. Colburn hacia la Meseta del lago Buenos Aires y sectores adyacentes (Santa Cruz, Argentina), se discute la procedencia geográfica de los holotipos de los roedores Eligmodontia morgani J. Allen, 1901 (Cricetidae) y Ctenomys colburni J. Allen, 1903 (Ctenomyidae). Para ambos taxones se restringen sus localidades típicas, cuya ubicación ha sido objeto de debate. Además, se refina información geográfica lograda por esta dupla de naturalistas para otros mamíferos patagónicos, en especial el ciervo Hippocamelus bisulcus.


Type localities of small mammals in Patagonia: Hatcher’s expedition to the Meseta del Lago Buenos Aires, Santa Cruz, Argentina. On the basis of a reconstruction of J.B. Hatcher y E.A. Colburn’s 1898 expedition to Patagonia’s Lake Buenos Aires region and intervening areas (Santa Cruz, Argentina), we discuss the geographic provenance of the holotypes of the rodents Eligmodontia morgani J. Allen, 1901 (Cricetidae) and Ctenomys colburni J. Allen, 1903 (Ctenomyidae). Type localities for both taxa have been the subject of debate, and new information allows us to restrict their location. Additionally, we provide geographic information about other mammals documented by them, most notably the Huemul (Hippocamelus bisulcus).

Riqueza de pequenos mamíferos não voadores em florestas de restinga do sul do Brasil

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Este estudo objetivou a caracterização da assembleia de pequenos mamíferos não voadores em termos de riqueza, abundância e sazonalidade na restinga do Parque Estadual Acaraí, localizado no nordeste de Santa Catarina. O sucesso total de captura foi de 2.78%, sendo 5.93% no inverno e 0.64% no verão. A espécie mais abundante e amplamente distribuída foi o roedor Akodon montensis (n = 71), com 56.35% dos indivíduos, seguido do roedor Nectomys squamipes (n = 42), com 33.33%, e do marsupial Marmosa paraguayana (n = 6), com 4.76%. O parque apresentou uma reduzida riqueza de espécies, ao ser comparado com outras áreas de restinga próximas.


Diversity of non-volant small mammals in Atlantic Coast restingas in the northeast of Santa Catarina, Brazil. This study aimed to characterize the community of non-volant small mammals in terms of richness, abundance, and seasonality in the restinga in the Parque Estadual Acaraí, state of Santa Catarina. The overall success of catch was 2.78% (5.93% in the winter and 0.64% in the summer). The most abundant and widely distributed species was Akodon montensis (n = 71), with 56.35% of the individuals, followed by Nectomys squamipes (n = 24), with 24.75%, and the marsupial Marmosa paraguayana (n = 6), with 4.76%. The park had reduced species richness compared with other nearby areas of restinga.

Localidades típicas de micromamíferos en Patagonia: el viaje de J. Hatcher en las nacientes del Río Chico, Santa Cruz, Argentina

Un estudio detallado del itinerario seguido por J. B. Hatcher y O. A. Peterson en las nacientes del río Chico, Santa Cruz, Argentina, permite discutir la procedencia geográfica de los holotipos de Ctenomys robustus J. Allen, 1903, Ctenomys sericeus J. Allen, 1903, Oxymycterus microtis J. Allen, 1903, Reithrodon hatcheri J. Allen 1903, Euneomys petersoni J. Allen, 1903 y Notiomys vestitus alleni Osgood, 1925. De esta forma se discute y restringen sus terrae typicae contribuyendo al conocimiento de la fauna de roedores patagónicos.


Type localities of small mammals in Patagonia: the travel of J. Hatcher in the headwaters of the río Chico, Santa Cruz, Argentina. A detailed study of the itinerary followed by J. B. Hatcher and O. A. Peterson in the upper course of the río Chico, Santa Cruz, Argentina, allowed us to discuss the geographic provenance of the holotypes of Ctenomys robustus J. Allen, 1903, Ctenomys sericeus J. Allen, 1903, Oxymycterus microtis J. Allen, 1903, Reithrodon hatcheri J. Allen 1903, Euneomys petersoni J. Allen, 1903, and Notiomys vestitus alleni Osgood, 1925. In this context we discuss and restrict their terrae typicae contributing to the knowledge of the Patagonian rodent fauna.

Roedores sigmodontinos del sitio arqueológico «El Divisadero Monte 6» (Holoceno Tardío, Buenos Aires, Argentina): taxonomía y reconstrucción ambiental

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Se describe el ensamble de roedores sigmodontinos recuperado en el sitio arqueológico «El Divisadero Monte 6», emplazado sobre la franja de humedales costeros de la Bahía de Samborombón (partido de General Lavalle, provincia de Buenos Aires, Argentina). Una datación de 540 ± 60 años radiocarbónicos antes del presente ubica la muestra en el Holoceno tardío. El ensamble está dominado por sigmodontinos frecuentes actualmente en el área (e.g., Akodon azarae, Oligoryzomys flavescens, Holochilus brasiliensis) y otros extintos regionalmente (e.g., Bibimys torresi, Pseudoryzomys simplex). La disminución de riqueza y diversidad que reflejan las comunidades actuales de sigmodontinos podría estar vinculada con el impacto antrópico que sufrió la región en los últimos siglos.


Sigmodontine rodents from “El Divisadero Monte 6” archaeological site (Late Holocene, Buenos Aires, Argentina): taxonomy and enviromental reconstruction. We describe the assemblage of sigmodontine rodents from the archaeological site “El Divisadero Monte 6”. This site is placed within the fringe of coastal wetlands of the Bahía de Samborombón (General Lavalle county, Buenos Aires Province, Argentina). A radiocarbon date of 540 ± 60 years B.P. indicates a Late Holocene age for the studied sample. The studied sample is mostly composed by species still frequent in the area (e.g., Akodon azarae, Oligoryzomys flavescens, Holochilus brasiliensis) and other sigmodontines regionally extinct (e.g., Bibimys torresi, Pseudoryzomys simplex). The observed decrease both in richness and diversity in recent samples probably was triggered by human-made disturbances over the pampean region during the last centuries.

Ecology of small terrestrial mammals in an isolated Cerrado patch, eastern Paraguay: communities, species, and effects of ENSO, precipitation, and fire

The Cerrado extends as islands or patches into the Upper Paraná Atlantic Forest (UPAF) of Brazil and Paraguay. This study evaluates the temporal dynamics of a marginal terrestrial small-mammal community in an isolated Cerrado patch within the UPAF, at the southwestern distributional limit of the Cerrado and near the western limit of the UPAF in eastern Paraguay. Because the faunal members of marginal communities are living near the limits of their capabilities in terms of their abiotic and biotic environment, the communities in such areas are likely to be a mixture of Cerrado and UPAF species, sensitive to extrinsic variables such as climate change and anthropogenic changes in land use. In this 23-month study, temporal dynamics of a terrestrial small-mammal community were evaluated with respect to El Niño / Southern Oscillation, precipitation, and fire. Densities of some species were quite variable. Generally, responses to precipitation patterns became evident only several months after burning, or (on the frequently-burned grid) were not observed. Some species more characteristic of forest or second-growth vegetation were encountered only seasonally or sporadically. Taken together, these observations provide strong support for the importance of long-term population studies in marginal or transitional locations, where two or more ecoregions are represented, and the fauna characteristic of each ecoregion will be sensitive to fluctuations in its biotic and abiotic environment.


Ecología de pequeños mamíferos terrestres en un parche aislado de Cerrado, Paraguay oriental: comunidades, especies y los efectos del ENSO, precipitación y fuego. El Cerrado se extiende en forma de islas o parches en el Bosque Atlántico del Alto Paraná (BAAPA) de Brasil y Paraguay. Esta investigación evalúa la dinámica temporal de una comunidad marginal de los mamíferos pequeños terrestres en un parche aislado de Cerrado dentro del BAAPA, en el límite de distribución suroeste del Cerrado y cerca del límite occidental del BAAPA en Paraguay oriental. Debido a que los miembros faunísticos de las comunidades marginales se encuentran viviendo cerca de los límites de sus capacidades en términos de sus ambientes abióticos y bióticos, las comunidades en dichas áreas posiblemente deben contener una combinación de especies de Cerrado y BAAPA, y ser sensibles a variables extrínsecas como cambios de clima, y de uso de suelo antropogénicos. Durante esta investigación de 23 meses, se evaluó la dinámica temporal con respecto a la Oscilación Sur / El Niño, la precipitación y el incendio. Las densidades de algunas especies fueron bastante variables. En general, las respuestas a los patrones de precipitación se hicieron evidentes solamente varios meses después de las quemas, o (en la parcela frecuentemente quemada) no fueron observadas. Algunas especies, más características de bosques o de vegetación secundaria, fueron encontradas solamente en forma esporádica o estacionalmente. En conjunto, estas observaciones proporcionan una fuerte evidencia sobre la importancia de los estudios poblacionales a largo plazo en áreas marginales o transicionales, en donde dos o más ecorregiones están representadas, y la fauna característica de cada ecorregión será susceptible a fluctuaciones de su ambiente biótico y abiótico.

Graomys hypogaeus Cabrera, 1934 es un sinónimo de Eligmodontia moreni (Thomas, 1896)

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Se estudió el holotipo de Graomys hypogaeus Cabrera, 1934, una especie correspondiente al género Eligmodontia de acuerdo a autores previos. Sobre la base de caracteres morfológicos y métricos se concluye que G. hypogaeus debe ser considerado un sinónimo junior de Eligmodontia moreni (Thomas, 1896), una especie ampliamente distribuida en el centro-oeste de Argentina.


Graomys hypogaeus Cabrera, 1934 is a synonym of Eligmodontia moreni (Thomas, 1896). We studied the holotype of Graomys hypogaeus Cabrera, 1934, a putative species of Eligmodontia according to previous authors. Based on morphology and metrics we concluded that G. hypogaeus must be considered as a junior synonym of Eligmodontia moreni (Thomas, 1896), a species widely distributed in west-central Argentina.