Soledad Albanese

Differential use of vertical space by small mammals in the Monte Desert, Argentina

Abstract Space use in deserts usually has been considered only along the horizontal dimension; however, vertical structure could be an important variable for habitat segregation among small mammal species. Our study assessed the use of vertical space by small mammals of the Monte Desert by live-trapping animals at different heights. We recorded 1,336 captures of 4 rodent and 1 marsupial species in 27,600 trap nights. All 5 species were captured on the ground and in tree layers, but only the gray leaf-eared mouse (Graomys griseoflavus) and the desert mouse opossum (Thylamys pallidior) used vertical space appreciably. G. griseoflavus used the arboreal space independently of habitat, plant species, or branch diameter, whereas T. pallidior showed a more selective behavior, being present at greater heights and on large-diameter branches of Prosopis trees. All rodent species used lower more than higher parts of arboreal strata. They used vertical space more or only during the dry season when resource availability is low. Our study suggests that vertical structure offers greater opportunities to acquire resources when these are scarce and plays a role in the coexistence of small desert mammals.

Historia natural de un roedor raro del desierto argentino, Salinomys delicatus (Cricetidae: Sigmodontinae)

El raton delicado de los salares (Salinomys delicatus) es un pequeno roedor endemico de Argentina. Ha sido considerado como vulnerable a la extincion dada su distribucion restringida y en parches, tamano poblacional pequeno y especializacion en habitats salinos. A pesar de que el raton delicado tiene adaptaciones morfologicas y fisiologicas para la supervivencia en ambientes aridos y salitrosos, poco es lo que se conoce de su historia natural. El presente trabajo tiene como objetivo estudiar la historia natural de S. delicatus, reportar nuevas localidades de ocurrencia, caracterizar el uso de habitat, su dieta y el ensamble acompanante, y describir su biologia reproductiva y morfologia. Se registraron dos nuevos sitios de ocurrencia en ambientes de bosques en galeria y bajos salinos en la region noreste de la provincia de Mendoza (Argentina), siendo las primeras citas para esta provincia. S. delicatus presenta una dieta omnivora, como es frecuente en otros roedores de desierto, y consume en igual medida semillas, artropodos y plantas halofitas. El ensamble acompanante esta compuesto por no mas de tres especies de pequenos mamiferos que varian segun la localidad, siendo esta riqueza similar a otros sitios del Monte. La proporcion de sexos y el patron de dimorfismo sexual mostraron un marcado desvio hacia las hembras (H:M = 3.6:1.1 y H:M = 1.151 respectivamente). La morfologia externa y craneal presenta una importante variabilidad intra e interpoblacional, sugiriendo que el aislamiento juega un rol importante. Cuando se consideraron adultos y juveniles, conjuntamente dos de las seis medidas externas (longitud total y longitud de cabeza y cuerpo) y siete de las 22 medidas craneales resultaron significativamente mayores en hembras que en machos. Cuando se compararon solo los adultos, cuatro caracteristicas externas (longitud total, longitud de cabeza y cuerpo, largo de la cola y peso) y seis medidas craneales fueron significativamente mayores en hembras que en machos. Este trabajo refuerza la importancia del desarrollo de nuevos estudios mas detallados sobre la historia de vida de S. delicatus y permite reafirmar la importancia de conservacion de esta especie.

Unvarying diet of a Neotropical desert marsupial inhabiting a variable environment: the case of Thylamys pallidior

Studies on the diet and other aspects of the natural history of Neotropical marsupials have focused mainly on a few species from tropical and forest habitats. Research on desert marsupials, on the other hand, is almost absent outside Australia. The desert mouse opossum, Thylamys pallidior, is a small marsupial which inhabits the arid lands of Argentina, Chile, Bolivia, and Peru. In Argentina, it occurs in the Monte desert, a highly seasonal system with a heterogeneous landscape which affords a good opportunity to perform comparisons among different environmental situations. We analyzed fecal samples from 123 individuals and compared their diet among different seasons, habitat types, sexes, and ages. The diet of T. pallidior was composed of 68.7% of arthropods and 31.3% of plant material, mainly leaves (24.6%). We found no significant differences in the proportions of any main food category consumed for any of the factors analyzed. Consumption of both plant and animal material seems to be important in the diet of T. pallidior which manages to keep their proportions constant despite the strong variability and seasonality of the habitat. Contrary to most didelphid species, but similarly to most mammals of this area, leaves seem to represent an important source of food possibly because of their abundance and stability in the Monte desert. This represents the first study to focus on the diet of a Thylamys species inhabiting an arid environment.