The structure of mesopredators' communities is complex and results from a multidimensional web of interactions such as top-down and bottom-up regulation or intraguild interactions. However, these interactions may change geographically along species' distribution ranges. The pine marten (Martes martes) and stone marten (Martes foina) are 2 similar-sized mustelids with overlapping ecological traits and a wide distribution overlap. The absence of stone martens from potentially adequate areas has been advocated as resulting from competitive exclusion by pine martens. Particularly, the preference of both species for mammalian rodents could be the main driver of such competitive stress. However, their elusive behavior and morphological similarity of their scats often precluded the evaluation of their ecological traits in areas of co-occurrence. Using camera trapping and diet analysis on genetically identified scats, we evaluated the interactions between pine and stone martens in the southwestern limit of their range along 3 ecological niche dimensions: spatial, trophic, and temporal, under a hypothesis of competitive dominance of pine martens. We found no spatial segregation, and that coexistence was facilitated by seasonally adjusted shifts along the trophic and temporal axes. While both species often co-occurred, during the season of low food resources, pine martens exploited the less profitable feeding resource. Moreover, they not only displayed an activity pattern that limited their access to rodents, but also reduced the probabilities of direct encounters with stone martens. We suggest that the dominance position has changed in favor of the stone marten in our study area, probably as a result of habitat quality and range edge effects. These findings support the relative instability of interspecific interactions among similar-sized species, which should be evaluated using multidimensional and site-specific approaches.