STRUCTURE AND FLORISTICS OF HABITATS ASSOCIATED WITH 5 RODENT SPECIESIN AN AGROECOSYSTEM IN CENTRAL ARGENTINA

Microhabitat use for five rodent species (Calomys musculinus, Calomys laucha, Akodon azarae, Oligoryzomys flavescens and Bolomys obscurus) i nhabiting agroecosystems of the central Argentine pampa was investigat ed for 17 months at six mark-recapture grids. Thirteen vegetation vari ables were measured along 748 transects at trap stations where rodents were captured and 252 stations where no captures were made. Principal components analysis was used to describe physiognomic differences amo ng crop and post-harvest habitats, as well as the less-disturbed borde rs of crop fields. Multiple logistic regression was used to assess the significance of principal components in predicting the presence of ro dent species. Associations of rodents with plant species in border hab itats were explored with Two-Way-Indicator-Species Analysis and corres pondence analysis.Aerial coverage by vegetation, as well as ground cov er by litter, and graminoid species richness, were important variables in predicting the presence of all rodent species, except C. laucha. V ertical vegetation density and maximum height were also important in d etermining the presence of C. musculinus in soybean fields. Within bor der habitats, C. laucha was found in lower quality microhabitats (incr eased bare ground, decreased vegetative cover, and decreased vertical vegetation density) and was associated with the invasive, introduced g rass, Cynodon dactylon. C. laucha was restricted to apparently sub-opt imal areas within border habitats during periods of high rodent densit y. These data indicate subtle differences in rodent-plant associations among the members of the rodent assemblage and possible competitive e xclusion of C. laucha from stable habitats. Calomys musculinus is the principal reservoir for Junin virus, aetiological agent of Argentine h aemorrhagic fever. These results have practical implications in helpin g define the risk of human disease on a fine scale and provide a theor etical basis for reservoir control and risk reduction.