Habitat use and diet in sympatric species of rodents of the low Parana delta, Argentina

Plant cover availability has been mentioned as one of the most important resources determining cricetid habitat use. In this paper, we describe the effect of variations in the principal dietary items (identified through in situ dietary studies) on the use of low and up-habitats by Oxymycterus rutilans, Akodon azarae, Scapteromys tumidus and Olygoryzomys delticola, in the low delta from Buenos Aires. Our results show that A. azarae feed mainly on invertebrates and to a lesser degree, on plant remains. Invertebrates are also the principal item in S. tumidus and O. rutilans diet, while O. delticola prefer green remnants. Both S. tumidus and O. delticola use low habitats all year round, while A. azarae and O. rutilans show seasonal variations in their habitat preference. In neither case, seasonal variations were associated to food availability. We suggest that the morphological adaptations to amphibious life of S. tumidus and the climbing habits of O. delticola made these species more efficient in low habitat (i.e., floodable and with an arboreal-shrub stratus), than A. azarae and O. rutilans. In the latter species, the seasonal variations of their habitat use seem to be a strategy used by populations to avoid the negative effects of extreme temperatures.