Long-term variations in rodent abundance in a rural landscape of the Pampas, Argentina

Relatedness dynamics and sex-biased dispersal in a seasonal cycle of corn mice from intensively managed agroecosystems

The sex-biased dispersal and kinship dynamics are important factors shaping the spatial distribution of individuals and are key parameters affecting a variety of ecological and evolutionary processes. Here, we studied the spatial distribution of related individuals within a population of corn mice Calomys musculinus in a seasonal cycle to infer dispersal patterns. The sampling was carried out from spring 2005 to winter 2006 in field borders of intensively managed agroecosystems. Genotyping data from 346 individuals with 9 microsatellites showed spatial genetic structure was weak for males, but not for females. The results indicate a complex spatial kinship dynamic of related females across all seasons. Which, contrary to our expectations, dispersal distances decrease with the increase of the population abundance. Meanwhile, male dispersal distances were greater when population abundance increased and thus the availability of active females. Males disperse greater distances to mate and sire offspring with distant females as a possible inbreeding avoidance mechanism. This study shows that C. musculinus is capable of much greater scattering distances than previously reported and that dispersal occurs fluidly and without barriers across the agroecosystem. The indirect benefit of dispersal on individual fitness could be related to relaxing the competition in the natal area and increasing the mating rate. Our study highlights the value of combining genetic relatedness, fieldwork observations, and behavioral data to estimate dispersal at a fine geographical scale.

Environmental drivers of long-term variations in the abundance of the red hocicudo mouse (Oxymycterus rufus) in Pampas agroecosystems

During the 20th century, there has been an ongoing agricultural expansion and global warming, two of the main determinants influencing biodiversity changes in Argentina. The red hocicudo mouse (Oxymycterus rufus) inhabits subtropical grasslands and riparian habitats and has increased its abundance in recent years in central Argentina agroecosystems. This paper describes the long-term temporal changes in O. rufus abundance in Exaltación de la Cruz department, Buenos Aires province, Argentina, in relation to weather fluctuations and landscape features, as well as analyzes the spatio-temporal structure of captures of animals. We used generalized liner models, semivariograms, the Mantel test, and autocorrelation functions for the analysis of rodent data obtained from trappings conducted between 1984 and 2014. O. rufus showed an increase in abundance across the years of study, with its distribution depending on landscape features, such as habitat types and the distance to floodplains. Capture rates showed a spatio-temporal aggregation, suggesting expansion from previously occupied sites. O. rufus was more abundant at lower minimum temperatures in summer, higher precipitation in spring and summer, and lower precipitations in winter. Weather conditions affected O. rufus abundance, but there was local variation that differed from global patterns of climate change.

Modelling relative abundance of Oligoryzomys flavescens, an Orthohantavirus reservoir, in an endemic hantavirus pulmonary syndrome zone

Hantavirus pulmonary syndrome (HPS) is a zoonotic emerging infectious disease caused by New World orthohantaviruses (family Hantaviridae) hosted by rodents of the family Cricetidae. In Argentina, one of its main hosts is the sigmodontine rodent Oligoryzomys flavescens, a widely distributed mouse of the Pampas, Delta and Espinal ecoregions of central-east Argentina. Because the abundance of the reservoir and its proportion in the rodent community affects both virus prevalence and human exposure risk, its estimation throughout its known geographical distribution is of key importance for the design of public health strategies to prevent HPS. The aim of this study was therefore to model the relative abundance of O. flavescens in most of the Pampas ecoregion within Buenos Aires Province, Argentina, where hantavirus pulmonary syndrome is endemic. To do this we used owl-pellet samples collected between 2006 and 2008 from 51 sites distributed throughout most of Buenos Aires province. Mammalian prey in each pellet was identified to the lowest possible taxonomic level by examination of the skulls, dentaries and molars. We modelled the frequency of O. flavescens found in each sample as a function of climatic, environmental, and topographic data of each site. The two best models were applied to a Geo referential Information System to build maps of estimated frequency (as a proxy of relative abundance) within Buenos Aires province. Estimated relative abundance of O. flavescens in Buenos Aires province was significantly associated with annual mean temperature, annual precipitation and presence of freshwater bodies, and varied among sub-regions, with the Inland and Rolling Pampas being the regions with highest frequencies. Knowing in which areas O. flavescens abundance is expected to be higher can be used to concentrate limited sanitary efforts in those areas that are most needed in order to reduce transmission and increase detection.

Population survey of small rodents on islands located inside a region of endemism for hantavirus pulmonary syndrome

Ecological studies of rodent species, especially as reservoirs of zoonoses, can identify spatiotemporal conditions associated with irruptions of abundances, as well as predict areas and times with higher risk of disease transmission. The aims of this research were to describe and identify (i) the rodent community composition; (ii) their population structure and breeding season; (iii) temporal and spatial variations in their population abundance; and (iv) the environmental factors associated with these variations on islands of upper Paraná River Delta, a zone of endemism for hantavirus pulmonary syndrome (HPS) in Argentina (Entre Ríos and Santa Fe provinces). We carried out seasonal surveys over 3 years (2014–2017) with live capture traps on seven islands (natural protected areas and under livestock grazing). Three hundred seventy-seven sigmodontine rodents of seven species were captured. While the maximum richness was seven, only four species coexisted at most on an island at the same time. Although changes in reproduction were detected throughout the year, seasonality, land use, and vegetation structure did not explain changes in abundance of rodents. Rodent abundances were affected mainly by flooding-related factors and meteorological conditions (rainfall and temperatures). The recovery of rodent populations after river flooding was species-specific and heterogeneous. The abundance of Oxymycterus rufus and Akodon azarae was affected by El Niño Southern Oscillation (ENSO); A. azarae did not recover after the flood at least during the study period. After the flood, populations of Oligoryzomys flavescens, the reservoir of HPS, also declined; however, this species’ populations were the first to recover its numbers, becoming dominant in the post-flood rodent community.

Weather and agricultural intensification determine the breeding performance of a small generalist predator

Land-use changes due to agricultural intensification and climatic factors can affect avian reproduction. We use a top predator of agroecosystems, the American kestrel (Falco sparverius) breeding in nest boxes in Central Argentina as a study subject to identify if these two drivers interact to affect birds breeding. We analyzed their breeding performance across a gradient of agricultural intensification from native forest, traditional farmland to intensive farmland. The surface devoted to soybean was used as a proxy of agriculture intensification; however, it did not affect the breeding performance of American kestrels. Even though the presence of pastures was important to determine the probability of breeding successfully. Climatic variables had strong effects on the species breeding timing, on the number of nestlings raised by breeding pairs and on the probability of those pairs to breed successfully (raising at least one fledgling). Our results highlight the relevance of pastures and grasslands for American kestrel reproduction. These environments are the most affected by land-use change to intensive agriculture, being transformed into fully agricultural lands mostly devoted to soybean production. Therefore, future expansion of intensive agriculture may negatively affect the average reproductive parameters of American Kestrels, at least at a regional scale. Further research will be needed to disentangle the mechanisms by which weather variables affect kestrel breeding parameters.

Evaluation of habitat requirements of small rodents and effectiveness of an ecologically-based management in a hantavirus-endemic natural protected area in Argentina

Hantavirus pulmonary syndrome is a severe cardio pulmonary disease transmitted to humans by sylvan rodents found in natural and rural environments. Disease transmission is closely linked to the ecology of animal reservoirs and abiotic factors such as habitat characteristics, season or climatic conditions. The main goals of this research were: to determine the biotic and abiotic factors affecting richness and abundance of rodent species at different spatial scales, to evaluate different methodologies for studying population of small rodents, and to describe and analyze an ecologically-based rodent management experience in a highly touristic area. A 4-year study of small rodent ecology was conducted between April 2007 and August 2011 in the most relevant habitats of El Palmar National Park, Argentina. Management involved a wide range of control and prevention measures, including poisoning, culling and habitat modification. A total of 172 individuals of 5 species were captured with a trapping effort of 13 860 traps-nights (1.24 individuals/100 traps-nights). Five rodent species were captured, including 2 hantavirus-host species, Oligoryzomys nigripes and Akodon azarae. Oligoryzomys nigripes, host of a hantavirus that is pathogenic in humans, was the most abundant species and the only one found in all the studied habitats. Our results are inconsistent with the dilution effect hypothesis. The present study demonstrates that sylvan rodent species, including the hantavirus-host species, have distinct local habitat selection and temporal variation patterns in abundance, which may influence the risk of human exposure to hantavirus and may have practical implications for disease transmission as well as for reservoir management.