Volumen y Número: Vol. 13

Habitat use and natural history of small mammals in the central Paraguayan Chaco

I conducted a small mammal trapping study in the central Paraguayan Chaco region of South America to investigate habitat selection by small mammals at different spatial scales. Small mammals were collected in forest, successional thorn scrub, pasture, and crop fields representing both relatively undisturbed habitats and agroecosystems. A total of 1,089 small mammals representing 13 species were captured during 23296 trap nights. Pastures had the highest species richness as well as the highest number of captures. Some small mammal species such as Calomys laucha and Akodon toba were captured in a variety of habitats whereas others like Holochilus chacarius and Bolomys lasiurus were captured almost exclusively in pastures. Principal components analysis distinguished small mammal species primarily associated with agricultural habitats (e.g. Calomys spp.) from those associated with more wooded habitats (e.g. Graomys griseoflavus and Oligoryzomys chacoensis). These results corroborate other studies on habitat use by small mammals in this region, but with some notable exceptions, such as the first documentation of high densities of Calomys musculinus in western Paraguay.

Los mamíferos finipleistocénicos de la Formación Quebrada Quereo (IV Región, Chile): biogeografía, bioestratigrafía e inferencias paleoambientales

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The Late Pleistocene mammal record of Quebrada Quereo Formation: biogeography, biostratigraphy and paleoclimatic inferences. This paper describes the fossil fauna recovered from the Quebrada Quereo Formation (Late Pleistocene – Holocene) located at Choapa Province, IV Region, Chile. In this formation, two cultural levels (Quereo I y II) with Pleistocenic fauna were detected. The remains identified include living species (Dusycion cf. D. culpaeus), as well as extinguished fauna (Palaeolama sp., Antifer sp., Equus [Amerhippus] sp., cf. Panthera onca, Milodontidae, and Gomphoteriidae). For each of these, we present taxonomic, paleogeographic and paleoclimatic remarks. The possible presence of P. onca in Quebrada Quereo Formation constitutes the first evidence of a locally extinct felid outside the Patagonic area of Chile. The identified faunal assemblage presents differences with those recorded in Argentinean territory; which is explained by the presence of the Cordillera de los Andes. The Chilean paleofaunistic assemblages, therefore, are related to those found in Bolivia and the Andean occidental sector in general, although some enrichment with taxa from the oriental side of the range is not discarded.

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.