Volumen y Número: Nº 2

Human use and small mammal communities of Araucaria forests in Neuquén, Argentina

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Small mammals were sampled in five closed, humid, Araucaria araucana forests that differed in the degree of anthropogenic disturbance in southwestern Neuquén Province. Nine species were captured in 3416 trap nights. Abrothrix longipilis and Oligoryzomys longicaudatus made up 88% of all captures. Small mammal relative abundance was 52 times higher where grazing was absent compared to a site with intense grazing pressure. Seed predation, primarily by livestock and feral exotic mammals, varied from 59.7% to 15.1% of marked seeds per day. Small mammal community productivity and composition were correlated with understory structure (Mantel test, r = 0.529, p = 0.04), and with rates of seed predation (r = -0.91, n = 4, p = 0.08). Forests with less complex understories had fewer captures and lower mammal diversity. Exotic large mammals appear to affect native small mammals by simplifying the structure of the forest understory and by competing for seeds. Four native species (Abrothrix longipilis, Oligoryzomys longicaudatus, Chelemys macronyx, and Irenomys tarsalis) ate Araucaria piñones. Anthropogenic changes in small mammal communities indicate that management of feral and domestic mammals needs to be a prominent part of the conservation of these majestic forests.

Predictive distribution maps of rodent reservoir species of zoonoses in southern America

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We model potential distribution for three species of rodents known to be reservoirs of zoonotic diseases: Calomys musculinus, Oligoryzomys flavescens and O. longicaudatus.
These models provide general distribution hypotheses obtained using environmental data from record localities. Satellite remote sensing is then used to extrapolate climatic and
ecological features of potentially suitable habitats for these rodents. In the three species mapped, we found high overall correspondence between predicted (based on environmental data) and specimen based distributions. The maps proposed here provide several advantages over dot and shaded outline maps. First, the predictive maps incorporate geographically explicit predictions of potential distribution into the test. Second, the validity of the predictive map can be appreciated when localities of previous records of the studied species, not used as training sites or used as control sites, are overlaid on the map. In this approach, environmental factors, criteria and analytical techniques are explicit and can be easily verified. Hence, we can temporally fit data in more precise distribution maps.

Expansión poblacional de una especie introducida en la Argentina: la ardilla de vientre rojo Callosciurus erythraeus

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Population expansion of an exotic mammal in Argentina: the Red-Bellied Squirrel Callosciurus erythraeus. Biological invasions are one of the major threats to biodiversity and ecosystem functioning, and they provoke economic losses to productive systems. A wild population of the Red-Bellied Squirrel Callosciurus erythraeus, native to South-east Asia, has established in the Province of Buenos Aires (Argentina) since 1973. The objective of this study is to assess the spatial distribution of the Red-Bellied Squirrel and describe the opinion of local inhabitants regarding the presence of this exotic species. We conducted 312 interviews in the district of Luján (original release site of this species) and other neighbouring districts, between August 2003 and March 2004. The area of the range distribution of squirrels was calculated using the minimum convex polygon method in a geographical information system. The present distribution of the Red-Bellied Squirrels (the only squirrel species present in this region) covers an area of approximately 680 km2. The increment of the radial distribution of squirrels was larger during the last five years (1999–2004: 1.6 km/year) than in a previous period (1973–1999: 0.3 km/year). While some inhabitants and local producers reported that the squirrels caused economic damages (e.g. in fruit plantations, afforestations, electric and irrigation systems), other inhabitants enjoy the presence of this species given its ornamental value, as a pet and even as a tourist attraction. The latter may encourage the transport of squirrels creating new invasive points, as has already occurred in the province of Córdoba (Argentina), and generating one of the major difficulties to prevent further expansion of this species.

Main food categories in diets of Sigmodontine rodents in the Monte (Argentina)

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The present study aims at improving the characterization of the dietary status of four Sigmodontine rodents (Graomys griseoflavus, Akodon molinae, Calomys musculinus
and Eligmodontia typus) by quantifying the major food categories (leaves, stems, seeds, Prosopis flexuosa pods, and arthopods) with a modified microhistological technique. The use of this new technique enhances the likelihood of accurately identifying plant parts, such as stems, seeds and fruits that are usually underestimated. Results reveal that hard tissues, like seeds, are a major resource in the diets while other hard tissues, such as stems and P. flexuosa pods, appear for the first time in the diet of all four species of Sigmodontine rodents. Rodent species display considerable trophic flexibility that may be particularly advantageous in arid environments where resource availability is unpredictable and heterogeneous.

Mammals of the Cosigüina Peninsula of Nicaragua

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Nicaragua’s Cosigüina Peninsula, located at the northwestern tip of the country, is one of the most poorly studied biotic regions in Central America. The peninsula has been
occupied for millennia because the climate of the region supported human habitation and because of its strategic position along the rich Pacific coast. The combination of long-term occupancy by humans and the cataclysmic eruptions of Volcán Cosigüina have produced a heavily impacted landscape. During the 1960s, the University of Kansas conducted multiyear field surveys of the terrestrial mammals on the peninsula and the adjacent mainland to quantify species diversity, relationships, abundances, habitat use, and reproduction. The mammalian fauna of the peninsula contains at least 39 species of terrestrial mammals, which includes 7 orders and 17 families. These include Didelphimorphia (2 species)—Didelphidae, 2; Chiroptera (22)—Emballonuridae, 2; Noctilionidae, 1; Mormoopidae, 1; Phyllostomidae, 12; Vespertilionidae, 3; Molossidae, 3; Carnivora (4)—Procyonidae, 1; Mustelidae, 1; Felidae, 2; Perissodactyla (1)—Tapiridae, 1; Artiodactyla (1)—Cervidae, 1; Rodentia (8)—Sciuridae, 1; Heteromyidae, 1; Muridae, 5; Dasyproctidae, 1; Lagomorpha (1)—Leporidae, 1. We provide new information on distributions, systematics, morphometrics, and natural history of the species of terrestrial mammals on the Cosigüina Peninsula, including a number of new records for the peninsula. We document that diversity and abundances of mammals can be substantial in a heavily impacted landscape. In comparison with five other mammalian faunas in Nicaragua, the Cosigüina fauna is most similar in size and diversity with those from elsewhere in the Pacific lowlands. The fauna from the Cordillera los Maribios, which is composed of the volcanic peaks along the eastern edge of the Pacific Lowlands, has the lowest number of species recorded for any of the six faunas with only 21 species recorded; however, this fauna may be under sampled or the unstable environments offered by these active volcanoes may not support a large or diverse mammalian fauna. The mammalian faunas from the remaining two physiographic regions of Nicaragua—Central Highlands and Atlantic Lowlands—have larger, more diverse faunas than that of the Cosigüina Peninsula and elsewhere in the Pacific lowlands. Three reserves in Nicaragua’s Sistema Nacional de Áreas Protegidas now protect more than one fourth of the peninsula.

Áreas de acción en un ensamble de roedores del desierto del Monte (Mendoza, Argentina)

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Home range of a rodent population in the Monte desert (Mendoza, Argentina). In the central portion of the Monte desert four small rodent species coexist: Graomys griseoflavus, Akodon molinae, Eligmodontia typus, and Calomys musculinus. Using the Convex Polygon Method, we assessed the home range of these species at different habitats and made comparisons among species, and between sexes and different seasons of the year. We found that home range did not differ among species, but there is a tendency to increase range size as the species corporal size increases. Overlapping of home range was different at different seasons of the year, probably due to different population densities, but home range size was constant along the year. Habitat type and sex affect home range only for G. griseoflavus and A. molinae, respectively.

Biologia reprodutiva de Delomys dorsalis (Hensel, 1872) —Rodentia, Sigmodontinae— em área de floresta ombrófila mista, Rio Grande do Sul, Brasil

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Reproductive biology of Delomys dorsalis (Hensel, 1872)—Rodentia, Sigmodontinae—in an area of mixed forest with conifers, at Rio Grande do Sul, Brasil. Delomys dorsalis is restricted to the wet tropical and subtropical forests of southern and southeastern Brazil and northeastern Argentina. The reproductive cycle of this species was studied by the histological examination of the reproductive tracts of animals caught in an area of mixed forest with conifers (29° 23′ S, 50° 23′ W), in southern Brazil, and from observations on a laboratory group of individuals. Fourteen expeditions were carried out from February 1997 to April 1998, during approximately 3 nights, using 140 live traps set on the ground and on branches between 1.5 and 2.0 m high. Reproductively active individuals were observed year round, although winter was marked by a reduction in breeding activity resulting from recruitment. Females showed a post-partum oestrus and a gestation time between 21 and 22 days. The litter size in captivity ranged from two to four, though pregnant females collected from the field had even five embryos. External reproductive features, frequently used as indicatives of the reproductive status of small mammals in ecological studies, were not accurate and underestimated the number of active animals in the population. Some individuals showed a remarkable scansorial ability that should be considered in future studies about population dynamics.