No abstract

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 Oil· goryzomys 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.Resume. -Nous avons analyse Peffet de la selection de l'habitat densite-dependante, et de la competition interspecifique sur 1'utilisation de 1'espace par les especes de petits rongeurs qui vivent dans les agroecosystemes. Nous avons etudie l'abondance des rongeurs dans les champs cultives et leurs limites, des bordures couvertes d'herbe moins perturbees par les acti-vites agricoles. On distingue deux categories d'especes : celles qui ne tolerent pas de variation de leur habitat, Akodon azarae et Oligoryzomys flavescens qui choisissent les bordures, et celles qui sont tolerantes, Calomys laucha et Calomys musculinus. Les deux especes les plus importantes dans la communaute, A. azarae et C. laucha, different dans leur utilisation de l'habitat. La premiere a une nette preference pour les bordures, tandis que 1'autre est repartie plus egalement dans les differents habitats, bien qu'elle soit plus abondante dans les champs. Les deux especes manifestent une tendance ä un usage accru des champs par intermediate d'une selection de l'habitat densite -dependante, avec une abundance qui s'accroit ä certains moments de 1'annee. C. musculinus ne montre en aucune saison de preference d'habitat, se trouvant avec 1'autre espece dans les deux habitats. II y a un effet interspecifique sur ('utilisation de l'habitat entre A. azarae et C. laucha: tandis que la premiere espece cause un changement dans la preference d'habitat de C. laucha vers les champs, cette derniere espece affecte l'utilisation de l'habitat densite-dependante de A. azarae. On conclut que le schema d'utilisation de l'habitat par les espe...

We studied the effect of removing Akodon azarae (Muridae, Sigmodontinae) on community and demographic parameters of rodent species in crop field borders of Central Argentina. We applied three replicated treatments: enclosure and removal of A. azarae, enclosure without removal, and a control without removal or enclosure. We conducted 14 monthly capture-mark-recapture samplings between October 1988 and March 1990. During the study period we observed an increase in Mus domesticus (Muridae, Murinae) abundance in removal areas. Other species did not respond to A. azarae removal. When A. azarae was removed, M. domesticus appeared to be competitively dominant over the remaining species of the community, increasing its relative abundance. Reproductive parameters of M. domesticus were more sensitive to treatments than survival parameters.