prey selection

Selección de presas de Thylamys bruchi (Marsupialia, Didelphidae) en el Desierto del Monte central, Argentina

Thylamys bruchi es un pequeño marsupial endémico de Argentina que habita el Desierto del Monte; es una especie nocturna y escansorial (i.e. utiliza estrato terrestre y arbóreo). Su dieta es omnívora con tendencia a la insectivoría, independientemente de las fluctuaciones en la disponibilidad de alimento. Este estudio tiene por objetivo evaluar la estrategia alimentaria de T. bruchi analizando estacionalmente la selección de presas y la amplitud de nicho trófico. El trabajo se realizó en la Reserva de Biósfera Ñacuñán, Mendoza, durante las estaciones húmeda y seca de 2014 y 2016. Este estudio se centró en conocer la composición de artrópodos de la dieta y para ello se analizó su consumo y su disponibilidad en el ambiente en las distintas estaciones. La dieta de esta especie presentó poca variabilidad estacional, con una composición de 70% artrópodos y 30% material vegetal. Se identificaron ocho órdenes y una familia de artrópodos, siendo Lepidoptera el más consumido. T. bruchi seleccionó lepidópteros (adultos y larvas) y ortópteros en todas las estaciones. La amplitud de nicho fue mayor en épocas de menor disponibilidad de presas, y menor cuando la abundancia fue mayor. Si bien T. bruchi presenta una estrategia alimentaria generalista, frente a los cambios estacionales en las presas incorpora la mayoría de los ítems disponibles y modifica parcialmente la composición de su dieta al aprovechar ítems más abundantes. Esta flexibilidad y el consumo de ítems alimentarios con mucha energía, como los artrópodos, permitiría que T. bruchi sobreviva en ambientes poco favorables como los desiertos.

Prey selection of Thylamys bruchi (Marsupialia, Didelphidae) in Central Monte Desert, Argentina. Thylamys bruchi is a small and endemic marsupial from Argentina which inhabits the Monte Desert. It presents nocturnal and scansorial habits (i.e. uses terrestrial and arboreal strata) and its diet is omnivorous with a tendency to insectivory, regardless of the fluctuations in food availability. The aim of this study was to evaluate the feeding strategy of T. bruchi seasonally, analyzing the selection of prey and the trophic niche breadth. Fieldwork was carried out at the Ñacuñan Man and Biosphere Reserve, Mendoza, during the wet and dry season of 2014 and 2016. This study focused on assessing the composition of arthropods in the diet. For this purpose, we measured prey consumption and their availability in the environment in the different seasons. T. bruchi‘s diet presented little seasonal variability, with 70% arthropods and 30% plant material. Eight orders and one family of arthropods were identified, with Lepidoptera being the most consumed item. T. bruchi selected Lepidoptera (adults and larvae) and Orthoptera in all seasons. Trophic niche breadth was greater in seasons with less prey availability and narrower when their abundance was greater. Although T. bruchi presents a generalist feeding strategy, in face of seasonal changes in prey abundance, it incorporates most of the available items and partially modifies the composition of its diet by exploiting more abundant items. This flexibility and the consumption of high energy food items such as arthropods may allow T. bruchi to survive in unfavorable and changing environments like deserts.

Variación espacial en la depredación por puma (Puma concolor) sobre guanacos (Lama guanicoe) en La Payunia, Mendoza, Argentina

María J. Bolgeri, Andrés J. Novaro

Estudiamos los patrones de depredación por puma sobre guanacos en dos sitios con diferente topografía en La Payunia, Mendoza, Argentina, analizando selección por sexo, edad y estado nutricional. La depredación fue la causa más frecuente de muerte (73%, n = 118 carcasas). En el sitio Este (más escarpado) los guanacos fueron depredados con mayor frecuencia que lo esperado en base a su densidad. No encontramos selección por parte de pumas por edades ni condición nutricional de guanacos, pero sí de machos por encima de hembras, a diferencia de otros estudios. En invierno, cuando se reduce el forraje, aumentó la frecuencia de carcasas en condición nutricional pobre.

Spatial variation in predation by pumas (Puma concolor) on guanacos (Lama guanicoe) in Payunia, Mendoza, Argentina. We studied patterns of puma predation on guanacos in two sites with different topography in La Payunia, Mendoza, Argentina, analyzing selection of prey by sex, age and nutritional condition. Predation was the most frequent mortality cause (73%, n = 118 carcasses) and was more frequent than expected according to guanaco density in the more rugged eastern site. We did not find prey selection by age nor nutritional condition, but pumas selected guanaco males over females, in contrast with other studies. In winter, when forage availability declines, the frequency of carcasses in poor nutritional condition increased.

Small mammal selection and functional response in the diet of the maned wolf, Chrysocyon brachyurus (Mammalia: Canidae), In southeast Brazil

Adriana A. Bueno, José C. Motta-Junior

Data reported here are intended to describe patterns of predation by a solitary hunter, as well as to bring new insights into the predator-prey relationship in the Neotropical region. The goal of this study was to verify if there was small mammal selection in the diet of the maned wolf. Also, we attempt to test for a functional response in relation to the consumption of small mammals. The study was carried out in the Ecological Station of Itirapina (ESI), São Paulo, Brazil. Faeces collection and small mammal abundance survey by pitfall trapping were conducted simultaneously during 2000–2002. The maned wolf was selective in the consumption of small mammals. Calomys tener and Oligoryzomys nigripes (Muridae) were consumed less than expected by chance, whereas Clyomys bishopi (Echimyidae) was preyed on more than expected. We did not detect a clear functional response by this canid in the ESI to overall shifts in abundance of small mammals. However, prey switching was detected by an increase in diet diversity in the wet season when small mammals become less available.