Roberto Murúa

Microhabitat selection in two Chilean cricetid rodents

SummaryA discriminant analysis on vegetational variables was performed in order to determine differences in habitat utilization by two sympatric Chilean rodents. Akodon olivaceus brachiotis is associated with vegetational variables that provide greater cover from above. Oryzomys longicaudatus philippii, on the other hand, is related with structural variables such as foliage density, which provide dense areas with thick understory that offer protection from a horizontal viewing. A clear relationship was found between shrub and herbaceous cover and length of species hindfoot.

The Small Mammal Community of a Chilean Temperate Rain Forest: Lack of Evidence of Competition between Dominant Species

Southern Chilean temperate rain forests support a diverse small mammal fauna comprised of both rodents and marsupials. Secondary growth forests have a less diverse fauna dominated by two sigmodontines, Akodon olivaceus and Oryzomys longicaudatus , with a scarcer third species, A. longipilis , usually present. To investigate interspecific interactions among these species, a series of reciprocal removal experiments was conducted in a coastal secondary growth forest during 1981–1982. All individuals of A. olivaceus and O. longicaudatus were removed from 0.5 ha open grids during monthly censuses. The population responses and demographic attributes of these and the unmanipulated species, A. longipilis , were monitored. During the experiment (duration = 21 months), the identities of the removed species were reversed after 12 months following characteristic annual population declines to zero. An unmanipulated 1.2 ha control grid provided baseline data. Monthly removals of A. olivaceus were found to be more effective than those of O. longicaudatus due primarily to rapid rates of immigration in the latter species. No significant effect of removals on the remaining dominant species was observed either during the whole study, the months of May–December 1981–82, or months in which removals were effective in lowering experimental grid densities below control grid levels. However, the third, scarcer species, A. longipilis , showed a significant ( P < 0.05) increase in population densities in response to removal of A. olivaceus during the latter two time units. While a reciprocal response might have been predicted among the ecologically similar akodonts, the lack of significant response to removals among the numerically dominant species as reflected in population densities or demographic attributes does not support the presence of major competitive effects between A. olivaceus and O. longicaudatus in this community.

Habitat utilization of two muroid species in relation to population outbreaks in southern temperate forests of Chile

Large-scale outbreaks of two species of rodents (Oligoryzomys longicaudatus and Abrothrix olivaceus) in response to a large increase in food resources in San Martin Experimental Preserve and in the Peulla area of the Vicente Perez Rosales National Park, were observed during fruiting and seedling of arborescent bamboo (Chusquea spp.). This unique phenomenon enabled the analysis of the effect of increased density on patterns of habitat use by these rodent species with mark-recapture grids in each area. Vegetation analysis was performed at three strata at each capture site. Associations between habitat variables and rodents presence or absence was assessed by using a logistic regressions. Habitat preference was strongly influenced by population density. Vegetation variables were important predictors for the presence of these rodent species only in years of low numbers. The results corroborate the predictions of the Fretwell-Lucas model of habitat selection

Second-order feedback and climatic effects determine the dynamics of a small rodent population in a temperate forest of South America

Abstract The multiannual cyclic fluctuations exhibited by arvicoline rodents in the Northern Hemisphere have attracted the attention of population ecologists. However, despite the abundant information on small rodent dynamics in South America, there are no studies reporting cyclic population dynamics. Here, we report evidence of cyclic population dynamics in a South American small rodent, the longhaired field mouse (Abrothrix longipilis) from southern temperate forests in Chile. The time-series analyses showed that longhaired field mice dynamics are better represented by a second-order autoregressive model characterized by 3-year cyclic dynamics. The 3-year cycles are clearly shown in the autocorrelation factor (ACF) pattern and in the dominant frequency of the spectral analysis. In addition, we determined nonlinear effects of the Antarctic Oscillation Index (AAOI). The results shown here pointed out that we need the integration of studies about cyclic small rodent populations from the different continents and beyond the Northern Hemisphere to resolve the enigma underlying the cyclic population dynamics exhibited by many small rodent species.

Comparative demography and diversity of small mammals in precordilleran temperate rainforests of Southern Chile

Small mammals were studied in two southern Chilean temperate rainforests in the precor-dillean Andes during 2 low-rainfall years following the 1982 El Nino event. Forests had somewhat different levels of canopy, shrub, and herbaceous cover, and species richness of trees but most of the same plants. Most captures were of four sigmodontine rodents, Akodon olivaceus, Abrothrix longipilis, Abrothrix sanborni , and Oligoryzomys longicaudatus ; five other species and a putative hybrid were recorded. Maximum numbers were in January–July (late summer to winter) and lower numbers in August–December (late winter to early summer). All species had seasonal reproduction in September–April (spring to autumn). A. olivaceus and A. longipilis generally were long-lived, whereas survival rates were low for O. longicaudatus . Responses after the 1982 El Nino were small, and some populations increased during 1984. Populations of A. olivaceus fluctuated more than those of A. longipilis ; those of A. sanborni were low and O. longicaudatus was sporadic and irruptive. Lower-elevational Chilean and precordilleran Argentine forests have similar species composition, but differences in demography and dominance of the former by more widespread, omnivorous A. olivaceus , animalivorous-fungivorous Abrothrix , and granivorous O. longicaudatus . Opportunities for immigration may explain greater homogeneity of populations of small mammals in Chilean rainforests relative to Argentine ones. Although responses to El Nino and subsequent droughts were weak, flowering episodes of bamboo ( Chusquea ) can have strong effects due to increased availability of food.

Ecología y evolución de hantavirus en el Cono Sur de América

Los hantavirus tienen huespedes especie especificos pertenecientes a una familia comun Muridae con tres sub familias, dos de ellas Murinae y Arvieolinae que se distribuyen en areas geograficas de Europa Asia y Oceania con un genero Arvicolinae en America del Norte y la Sub familia Sigmodontinae en Centro America y Sudamerica. Estudios de la filogenia del huesped y el virus muestran fuertes similitudes al ser comparados, lo que sugiere una asociacion de mucha mas larga data con un proceso de coevolucion entre el agente infeccioso y sus huespedes roedores. La historia de la tierra y los procesos tectonicos y climaticos que afectaron al continente en epocas preteritas son relevantes para comprender la actual distribucion de los reservorios huespedes y sus parasitos. Se entregan antecedentes biogeograficos de los roedores con la distribucion geografica de los hantavirus en Sudamerica, analisis filogenetico de los virus, epidemiologia molecular que sustentan la propuesta que el virus y el roedor han coevolucionado antes del momento de separarse la Familia Muridae en subfamilias (Murinae, Arvicolinae y Sigmodontinae) y anterior al ingreso de los roedores sigmodontinos al continente sudamericano. Se discute la dificultad en demarcar especie nueva de hantavirus y la existencia de varios linajes con diferencias pequenas entre si para ser consideradas como especies virales. Se describen diferencias y similitudes entre las dos especies de hantavirus que mas casos han producido en America del Norte (virus Sin Nombre) y en el Cono Sur de de America (Virus Andes).