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.

Bird occupancy in intensively managed agroecosystems under large-scale organic and conventional farming in Argentina: A multi-species approach.

Several studies in European and North American agroecosystems conclude that organic farming benefits birds compared to conventional farming. Nevertheless, there are some biases toward these geographic regions and farm size. Argentinian agroecosystems are particularly homogeneous with large arable fields and sparse uncultivated field margins (i.e. large-scale homogenous cropping systems). In Argentina only 0.55% of the total farmland is under organic farming. Thus, our aims were to assess differences in bird occupancy between organic versus conventional farming regimes, and whether bird occupancy varied in relation to annual crop proportion in both farming regimes in central Argentina agroecosystems. We surveyed 156 points in farms under conventional and 154 in organic farming regimes during two bird-breeding seasons. We used multi-species occupancy models with a Bayesian approach to estimate bird occupancy. We observed that the type of farming regime (organic in relation to conventional) had a weak effect on avian occupancy, varying by species and groups. Probability of occupancy was higher for a few insectivorous and omnivorous species but lower for carnivores in organic farms in relation to conventional ones. The proportion of annual crops was positively correlated with occupancy of an insectivore aerial forager, some insectivore foliage gleaners, a granivore, and some omnivorous species in organic farms, but not conventional farms. This work contributes to reducing geographic and small-scale heterogeneous cropping system biases in the avian agroecological literature. Our results, together with future studies needed to assess landscape configuration and composition, and resource availability for birds in each farming regime, will allow the evaluation of organic farming as a tool for the conservation of bird species in large-scale homogeneous cropping systems in temperate regions.

The landscape complexity relevance to farming effect assessment on small mammal occupancy in Argentinian farmlands.

The responses of organisms to organic farming depend on the taxonomic group and landscape complexity. Following the intermediate landscape complexity hypothesis, organic farming can compensate for the lack of complexity in simple landscapes. Argentinian farmlands are simple with large fields and scarce linear habitat array, and conventional agriculture is almost the only agriculture practice. We hypothesize that there is an interaction effect of landscape complexity and farming practices on occupancy and species richness of small mammals in farmland of central Argentina. We selected circular landscapes under organic farming and low- and high-intensity conventional farming and quantified heterogeneity in each landscape considering different cover types (crops, resting plots, fallow land, border habitats, grasslands and man-made structures). We used multi-species occupancy models accounting for multiple seasons with a Bayesian approach to make the estimates. Landscapes under organic farms had the highest level of landscape heterogeneity. In simple Argentinian farmlands, organic farming benefited species richness and occupancy of all small mammal species. Some management strategies used in organic farming (wide and vegetated border habitats, diversity in types of production, winter cover crops, natural or semi-natural patches) should be taken into account to increase landscape complexity in conventional farming.

Temporal and spatial host abundance and prevalence of Andes hantavirus in southern Argentina.

Andes virus (AND) is a hantavirus hosted by the sigmodontine rodent Oligoryzomys longicaudatus in southern Argentina, where it is responsible for most cases of hantavirus pulmonary syndrome (HPS). Our study provides data about the spatial variation in abundance of the rodent host of AND hantavirus. We report results of a longitudinal study performed in a locality of the Andean region of Chubut Province. From November 2003 (spring) to July 2006 (winter), O. longicaudatus was the most common species captured (63%) and it showed significant differences in abundance among habitats and seasons. Most antibody-positive rodents were O. longicaudatus (9.2%), followed by A. longipilis (3.6%) and A. olivaceus (1.5%). The highest number of antibody-positive animals was observed for males that belonged to the heaviest mass classes. Antibody-positive O. longicaudatus were more abundant in brush habitats. We found low richness of rodents and abundance of O. longicaudatus in areas affected by anthropogenic activity. The infection seems to be regionally persistent, but the risk to humans in a landscape would be localized. To develop accurate models for predicting HPS outbreaks, further research is needed to characterize rodent movement patterns across the landscape.