Spatial, Dietary and Temporal Niche Dimensions in Ecological Segregationof Two Sympatric, Congeneric Marsupial Species

Didelphis aurita and D. albiventris are widely distributed in South America, with a range of sympatry in the limit of their distribution, particularly in Araucaria mixed ombrophilous forest in the southern Atlantic Forest. We investigated the spatial, feeding, and time use between these morphologically similar species in a remnant of Araucaria forest in southern Brazil for one year. We tested the hypothesis that these species when in sympatry segregate each other in space use, diet, and/or activity time. We expect that they segregate between each other primarily in the dimension of space use, as occurs for Australian congeneric marsupials. We used a mark-capture-release protocol for obtaining data. We analysed the spatial segregation by measuring the distance of captures in relation to the remnant centre, stream and edges. There were significant differences in the use of space, as adult females of D. aurita used mainly the remnant interior and stream sides, and D. albiventris females its edges or open areas. The consumption of feeding resources, particularly fruits, was different mainly between females and during the breeding season. However, there was no difference in the activity time between species. We believe that the territorial behaviour of D. aurita females had a crucial role in this spatial segregation with D. albiventris females, leading to a diet differentiation, particularly for fruits which were highly available inside the remnant. Interspecific competition between females is thought to be the main reason maintaining D. albiventris females far from the richest parts of the remnant. The mechanism behind this ecological segregation is discussed, and an ecological niche shift when both species are in sympatry is suggested, rather than the ghost of competition past.