Niche overlap and resource partitioning between two sympatric fox species in southern Brazil

Mechanisms that favour the co‐occurrence of morphologically and ecologically similar species in South America are potentially relevant, because two or more species often occur in sympatry. In the present study, we investigated possible mechanisms of resource partitioning between two sympatric species of foxes, the crab‐eating foxCerdocyon thousand the pampas foxPseudalopex gymnocercus, in the National Park of Aparados da Serra in southern Brazil (29°10′S, 50°05′W). We considered three main niche dimensions – habitat, diet and time – and evaluated the overlap between the two species in these dimensions. We conducted the study from June 2000 to October 2001 in an area composed of open grasslands andAraucariaforests. We studied the foxes by using a combination of scat analysis and direct observation. A comparison of their diet indicated that it was very similar for both species in all seasons (Pianka's indexes ranging from 0.920 to 0.957). The most common food item for both species of foxes was rodents, followed by coleopterans, birds and plant remains (seeds and fruits). As expected by the niche‐complementarity hypothesis, we detected differences along other niche axes.Pseudalopex gymnocercusseemed to occur only in open areas, including grasslands and dirt roads, whereasC. thouswas more generalist in habitat use, occurring both inside and at the edge of forests. However, both fox species were common in grassland habitats, where they might compete for resources. The differences were more marked for activity time, with the crab‐eating fox being significantly more nocturnal (circular mean of time of sighting=23:39 h,se=56 min) than the pampas fox (circular mean=19:56 h,se=64 min; Watson'sF=6.06,P=0.02). We suggest that the largerC.thouscould be limiting the activity ofP.gymnocercusby interference competition.