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.


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. 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.

Incidencia de vizcachas (Lagostomus maximus) en un cultivo de soja

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Entre enero y mayo de 1994 se evaluó el daño por vizcachas (Lagostomus maximus) en un cultivo de soja de 14 ha, en el N de la provincia de Córdoba (Argentina). Se contaron las plantas remanentes en pie/m2 y se registró el peso total de semillas por vaina en tres sectores con signos de actividad de vizcachas y niveles diferentes de daño, ubicados a distancia creciente de las madrigueras. También se tomaron estos datos en otro sector más alejado (control), sin actividad de vizcachas ni daño aparente. El menor número de plantas remanentes/m² se encontró en el sector próximo a las vizcacheras. El peso total de semillas/vaina fue menor en los dos sectores cercanos a las madrigueras. El porcentaje de hojas de soja en la dieta, verificado mediante el análisis microhistológico de heces frescas, varió entre meses y entre cuevas situadas a diferentes distancias del cultivo. El mayor consumo se registró entre enero y marzo en aquellos individuos que habitaban madrigueras cercanas al cultivo (< 50 m). El daño fue restringido en superficie y relacionado con la cercanía del cultivo a las vizcacheras. Por lo tanto, las pérdidas dependerán de la superficie cultivada y del tamaño y ubicación de la población de vizcachas. En este caso, estas representaron un 3% del ingreso total del productor. Comparando los beneficios de erradicar este roedor y los de su uso sustentable, se concluye que este último es una alternativa para resolver conflictos en el manejo de las poblaciones de vizcacha.


Damage to a soybean crop by viscacha (Lagostomus maximus). From January to May 1994, we evaluated the damage produced by viscachas (Lagostomus maximus) to a 14-ha soybean crop in the N of Córdoba Province (Argentina). Measurements were carried out in three sectors with signs of activity of viscachas and different levels of damage, located at increasing distances from the burrows. Also, measurements were taken in an area (control) with no viscacha activity or apparent damage. We counted remanent plants/m² and weighed all the seeds per fruit. The lowest number of plants was found in the sector nearest the burrows. The lowest seed weight per fruit was recorded in the two sectors that were closest to the burrows. The percentage of leaf of soybean in the diet, verified by microhistological analysis of fresh feces, varied among months and among burrows located at different distances from the crop. The highest values were observed between January and March in those individuals that inhabit burrows near the crop (< 50 m). The damage was restricted in area and related to the proximity of the crop to the viscacha colonies. Therefore, the losses will be related to the size of the cultivated plot and to the size and location of the viscacha population. In this case, losses represented 3% of the farmer’s total income. Comparing the benefits of eradicating this rodent and those of its sustainable use, we conclude that the latter is an interesting alternative for solving conflicts in the management of the populations of viscachas.