Volumen y Número: Nº 1

Distribución de Necromys lactens y Phyllotis osilae (Rodentia: Cricetidae: Sigmodontinae) en el Noroeste argentino: modelos predictivos basados en el concepto de nicho ecológico

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Distribution of Necromys lactens and Phyllotis osilae (Rodentia: Cricetidae: Sigmodontinae) in northwestern Argentina: predictive models based on the concept of ecological niche. We used presence data from field records, museum specimens and literature sources to model the potential distribution of two species of sigmodontine rodents, Necromys lactens and Phyllotis osilae in northwestern Argentina, based on environmental variables. We used the DOMAIN program, which based on presence data defines the environmental space that imposes conditions to the species distribution. We worked with two data sets, one constituted only by reliable data and the other one constituted by these reliable data plus other information considered more doubtful because of its controvertible identification and location. The models obtained from the reliable data set were more efficient in the prediction of distribution than doubtful data, with Kappa index of 0.69 and 0.63 for Necromys lactens and Phyllotis osilae, respectively. These results indicate that both species are restricted to the upper portions of the most important mountains in the region and that their distribution consists of islands or patches immerse in a complex matrix of forest and semi-desert environment. Both species were associated to high altitude grasslands and ecotone environments between 1200 and 3200 m elevation, being P. osilae‘s distribution a little more extended than N. lactens.

Nuevas localidades argentinas para algunos roedores sigmodontinos (Rodentia: Cricetidae)

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New localities for sigmodontine rodents (Rodentia-Cricetidae) in Argentina. New localities for 24 species of sigmodontine rodents in Argentina are reported based on records obtained by direct trapping and/or the analyses of owl pellets. This report includes the first Argentinean record for Akodon boliviensis and Necromys amoenus. Additionally, we extend the known distribution for Akodon budini, A. sylvanus, A. toba, Necromys cf. N. lasiurus, Calomys musculinus, Loxodontomys micropus, Phyllotis osilae, P. xanthopygus, and Phyllotis wolffsohni. Finally, additional localities for Abrothrix illuteus, A. longipilis, Chelemys macronyx, Notiomys edwardsii, Necromys lactens, Bibimys chacoensis, Holochilus chacarius, Oecomys sp., Oryzomys angouya, O. legatus, Reithrodon auritus, Rhipidomys austrinus, and Euneomys mordax are reported. The results suggest that much work remains yet to be done in order to have an adequate picture of the diversity and distribution of Argentinean sigmodontine rodents.

Dinâmica populacional de marsupiais e roedores no Parque Municipal da Lagoa do Peri, Ilha de Santa Catarina, sul do Brasil

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Population dynamics of marsupials and rodents in Parque Municipal da Lagoa do Peri, Santa Catarina Island, southern Brazil. A two-year mark-recapture study of small mammals was conducted in an area of Atlantic Forest hillside in the state of Santa Catarina, Brazil. Four species of marsupial and seven species of rodent were captured during 12132 trap nights. Aspects of population dynamics and natural history are discussed for each common species. The sex ratio was biased toward males for all species. Oryzomys russatus, Didelphis aurita and Akodon montensis had the highest population densities, the least amount of variation in population density and an inverse relationship between survivorship rates and population densities. Micoureus paraguayanus, Nectomys squamipes and O. angouya registered the higher population densities after continual survivorship rates. The recruitment rates were low for most species (< 50%), with some, M. paraguayanus, Lutreolina crassicaudata, Oligoryzomys nigripes, O. angouya and Oxymycterus aff. judex, disappearing occasionally from the study area. The survivorship rates were high for most species (> 50%). Population densities of D. aurita, O. nigripes and O. aff. judex increased in cold and dry periods. The marsupials reproduced seasonally from late winter until the end of the summer, whereas rodents reproduced throughout the year. No species were long-lived, with average life-span < six months.

Molecular and phylogenetic analysis of mitochondrial control region in Robertsonian karyomorphs of Graomys griseoflavus (Rodentia, Sigmodontinae)

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The South American rodent Graomys griseoflavus is a species with a Robertsonian (Rb) autosomal polymorphism. A marked genetic differentiation between 2n = 42–41 and 2n = 38–34 karyomorphic groups was evidenced by cytogenetic and molecular analysis. The mitochondrial control region was sequenced in all Graomys karyomorphs for its characterization and used to trace more accurate phylogenetic relationships. The molecular organization showed to be coincident with the consensus molecular structure described for other rodent taxa, exhibiting the conserved domains ETAS (extended termination-associated sequences), CD (central domain) and CSB (conserved sequence block) 1, 2 and 3. Phylogenetic trees showed that 2n = 42–41 and 2n = 38–34 karyomorphic groups form separate clades, with neither phylogeographical structure nor population subdivision within Rb karyomorphs. These findings suggest a short evolutionary time for the occurrence and fixation of the chromosomal rearrangements and reinforce the single origin hypothesis for the Rb karyomorphs of G. griseoflavus.

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

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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.