Sharing the space: distribution, habitat segregation and delimitation of a new sympatric area of subterranean rodents

Abstract

Subterranean rodents of the genus Ctenomys usually present an allopatric or parapatric distribution. Currently, two cases of sympatry have been recognized for the genus in the coastal dunes of southern Argentina and southern Brazil. In this context, they are ideal models to test hypotheses about the factors that delimit the patterns of space use and to understand interspecific interactions in small mammals. We investigated the vegetation structure, plant biomass and soil hardness selected by two species of subterranean rodents (Ctenomys flamarioni and C. minutus) when distributed in sympatry and allopatry from nine different areas along the line of coastal dunes in southern Brazil. In addition, our work presents a new record of a third area of sympatry for the genus Ctenomys. Ctenomys flamarioni and C. minutus show habitat segregation in the area where they occur in sympatry. These species show segregation in their selection of microhabitats, differing in relation to soil hardness, plant biomass, and plant cover. Ctenomys flamarioni showed a distinction in habitat selection when occurring in allopatry and sympatry, whereas C. minutus selected the same habitat characteristics under both conditions. A possible explanation to the observed pattern is that these species have acquired different adaptations over time which allows them the ability to exploit different resources and thus avoid competitive interactions all together.

Fig 1. Geographic distribution of C. flamarioni and C. minutus in the coastal plain of southern Brazil.

Two sympatric areas are indicated in the map by letters: A—sympatric area cited by Freitas (1995); B—new sympatric area described by these species. South America map obtained from OpenStreetMap (free available at: http://www.openstreetmap.org/). The image was edited using CorelDraw graphics Suite.

Fig 2. Comparisons of soil hardness, plant biomass, grass cover and herb cover between C. flamarioni and C. minutus distributed in sympatric and allopatric areas.

Top and lower horizontal lines of boxes represent standard deviations. Black points and the center horizontal lines represent the mean and the median, respectively. The results of the statistical tests are displayed in the text. Asterisk indicates a significant difference and “ns”non-significant. For all the variables, the middle “*/ns” reflects a test between species, and the first and third “*/ns” reflect comparisons within species.

Fig 3. Principal component analysis (PCA) of habitat features selected by C. flamarioni (□) and C. minutus (+) species in sympatric area in the southern Brazilian coastal plain.