Understanding factors that influence the distribution and abundance of seed dispersers is important because of the role these species play in maintaining plant communities. The temperate forest of Patagonia has an unusually high frequency of mutualisms, including obligate seed dispersal of a keystone mistletoe (Tristerix corymbosus) by the marsupial Dromiciops gliroides. We examined whether the distribution and abundance of D. gliroides was related to the distribution and abundance of this mistletoe, which is a principal food source, or alternatively, whether other habitat features constrain the distribution and abundance of this marsupial. We conducted field surveys for D. gliroides, mistletoe, and other habitat variables and developed a set of habitat models in which model variables were defined a priori. We found that the distribution of D. gliroides was related to bamboo cover. Bamboo is an important source of nest material and nest sites. However, when the minimum requirement for bamboo cover was met, abundance of D. gliroides tracked abundance and fruit production of mistletoe plants. Habitat constraints imposed by bamboo on D. gliroides have important conservation implications because both anthropogenic and natural processes have significant impacts on bamboo in the temperate forest of Patagonia.