Descripción: We analyzed the effect of density-dependent habitat selection and interspecific competition on the use of space by small rodent species in agroecosystems. We studied rodent abundance in cropfields and their borders, weedy margins less disturbed by agricultural activities. We could distinguish two kind of species: those habitat intolerants, Akodon azarae and Oligoryzomys flavescens, which select the borders, and those habitat tolerants, Calomys laucha and Calomys musculinus. The two most abundant species in the community, A. azarae and C. Laucha, differ in their habitat use: while the first has a clear preference for borders, the other is more equally distributed between habitats, although it is more abundant in fields. Both species show a shift towards an increased use of fields via density-dependent habitat selection with increasing abundance at some moments of the year. C. musculinus does not show habitat preference in any season, overlaping with the other species in both habitats. There is an interspecific effect on habitat use between A. azarae and C. laucha : While the first species cause a shift in habitat preference of C. laucha towards fields, this latter species affects the density-dependent habitat use of A. azarae. It is concluded that the pattern of habitat use of the studied species is affected by their differential preferences as well as by intra and interspecific density-dependent processes that change seasonally.

Descripción: Competitive relationships between rodent species were studied in pampean agrosystems. Akodon azarae, Calomys laucha, Calomys musculinus and Oligoryzomys flavescens show a differential spatial distribution between cropfields and their borders in this system. The goal of this paper was to assess the role of competition in determining spatial distributions and relative abundances of these species. A removal experiment in border habitats showed that the removal of A. azarae causes an increase in captures, survival and residency time in C. laucha and O. flavescens (as compared to control areas). Removal of C. laucha didn't cause any change in the remaining species. Results showed that competition with A. azarae limits the use of field borders by C. laucha and O. flavescens. Presence of A. azarae in border habitats prevents the establishment of residents of C. laucha and O. flavescens, thereby causing also higher mortality and lower reproductive rates in these two species than those registered when A. azarae is removed. Interspecific encounters in a test arena showed that behavioral interactions are contributing to spatial segregation, with A. azarae becoming dominant over C. laucha. © 1993, Walter de Gruyter. All rights reserved.

Descripción: We report results of dietary analyses of Akodon azarae and Calomys laucha and of food availability in corn fields and their borders in the Pampean region of central Argentina. Sampling was conducted at different developmental crop stages, in order to assess the influence of food availability on diet and reproductive performance. Both species were generalistic and opportunistic feeders, but differed in food habits and nutritional requirements for reproduction : A azarae had omnivorous diets and its breeding activity was related to high requirements of insects, whereas C. laucha was mainly an herbivorous-granivorous feeder and required high amounts of green forage to improve its reproductive performance. We discuss the role that food availability may play as a potential factor for competitive interactions at the different crop stages, regarding the changes in abundance of both species and their differences in diet, competitive ability, habitat preferences and colonizing potential. © 1992, Walter de Gruyter. All rights reserved.

Descripción: Les relations interspecifiques entre une serie de rongeurs Cricetides ont ete etudiees dans des ecosystemes agraires de la province de Buenos-Aires de 1979 ä 1982. Leurs relations spatiales et numeriques ont ete analysees dans un Systeme de double habitat comprenant les champs cultives et leurs bordures. Une competition interspecifique asymetrique pour Pespace a ete mise en evidence, surtout pendant Fete chez 1‘espece dominante Akodon azarae^ et on a constate des differences individuelles dans 1’aptitude ä la competition. Les femelles de cette espece etaient plus dominantes que les males, et les juveniles de Calomys laucha etaient plus disperses que les adultes. Les mecanismes de coexistence d'especes differentes dans les bordures sont discutees. © 1992, Walter de Gruyter. Alle Rechte vorbehalten.

Descripción: We studied hantavirus seroprevalence and virus variability in rodent populations in Diego Gaynor, northwest of Buenos Aires province, Argentina. Rodent samplings were conducted in railroads and cropfield borders in March and July 1999, September and December 2000, and March 2001. Antibody detection was performed by an enzyme link immunosorbent assay (ELISA), using the recombinant nucleoprotein of Andes (AND) virus as antigen. Tissue samples were taken from positive antibody individuals in order to confirm the presence of hantavirus genomic material and to identify virus genotypes. Akodon azarae was the most abundant species, followed by Oligoryzomys flavescens, while Calomys laucha and C. musculinus were rarely caught. We found a rate of seroprevalence of 9.3% for a total sample of 291 A. azarae and 13.5% for 37 O. flavescens. After molecular analyses of hantavirus, we confirmed the presence of hantavirus genomic material in 16 individuals with ELISA (+) results and two individuals with ELISA (-). Four amplimers for each species were sequenced and compared to the corresponding sequences of representative hantaviruses. We identified the AND Cent Lee from three O. flavescens, and the Pergamino virus from four A. azarae and from one O. flavescens. A. azarae males had higher seroprevalence than females, and heavier individuals showed higher seroprevalence than lighter ones. We did not find seroprevalence differences according to sex in O. flavescens, although this result may have been produced by the low sample size. The lowest seroprevalence was found in a period of high rodent density, when juveniles prevailed in the population. We found higher seroprevalences than those detected in previous studies for other localities of central Argentina where cases of hantavirus pulmonary syndrome (HPS) have been reported. The presence of AND Cent Lee virus in rodent populations of the study area, which is responsible of HPS cases in central Argentina, suggests that human populations are at risk of HPS disease, although there were not reported cases of this disease until today.

Descripción: We experimentally assessed the effect of controlling vegetation height along farm perimeters on the abundance of rodents in 2 broiler poultry farms in central Argentina. We carried out an experimental design based on the before-after-control-impact method. After vegetation treatments, there was a significant decrease in rodent abundance at the perimeter of the farm with control of vegetation height because of the reduction of the Pampean grassland mouse Akodon azarae. In poultry houses, there was a significant decrease in rodent abundance on nonaffected farms because of the reduction of the commensal house mouse Mus musculus domesticus, possibly because of a major collocation of rodenticide. Our results indicate that both the control of vegetation growth at the perimeters and the appropriate timing of rodenticide applications are effective measures for rodent control on broiler poultry farms when both control measures are applied simultaneously. We achieved effective rodent control through an understanding of the habitat use and population dynamics of the species involved and the characteristics of the area where the control program would be applied. © 2009 Poultry Science Association, Inc.

Descripción: We studied the dietary niche of the Barn Owl (Tyto alba) in temperate agroecosystems of central Argentina by describing seasonal and geographic variation in the food habits of this owl in four districts of the Pampean region (Flooding, Inland, Rolling, and Southern Pampas). We identified 21,925 prey items from samples of fresh pellets collected in summer (n = 23) and winter (n = 26). Mammals,' mostly sigmodontine rodents, were the main prey items (91.9%), followed by amphibians (6.5%) and birds (1.6%). Arthropods were also a common prey item (found in 45% of the samples). The consumption of arthropods and amphibians was higher in summer than in winter, indicating that seasonal changes in prey abundances are reflected in the Barn Owl diet. We found no differences in food-niche breadth among the four study districts, but food-niche breadth varied between seasons, being higher during summer. Six rodent species were common to all districts: Calomys spp., Akodon azarae, Oligoryzomys flavescens, Mus musculus, Rattus spp., and Holochilus brasiliensis. Calomys spp. was numerically dominant in 46 of the 49 samples, and together with A. azarae and O. flavescens comprised the bulk of the diet (> 80%). Predation on rodents may reflect population dynamics of the prey species with high predation rates when peaks in abundance of sigmodontine rodents occurred (autumn-winter). © The Neotropical Ornithological Society.