Pulliam’s (1988) model of sources and sinks demonstrated the importance of considering spatial variation in demographic rates for understanding population persistence. One of the factors contributing to such spatial variation is variation in the occurrence of other species, including prey, predators and mutualists. Here we consider how such variation in community context affects what could be termed sources and sinks in the evolution of species interactions. We focus on the seed dispersal mutualism between Clark’s nutcrackers (Nucifraga columbiana) and limber pine (Pinus flexilis), and how the presence and absence of a seed predator, the red squirrel (Tamiasciurus hudsonicus), likely causes the mutualists to experience demographic sinks and sources, respectively. Although sink populations of limber pine mostly represent the later stages in forest succession, when limber pine trees are older, species interactions within the source and sink populations will affect the evolution and maintenance of the seed dispersal mutualism. In general, the persistence of mutualisms is probably dependent on the amount of habitat that lacks a competitively superior antagonist (i.e., a “source” habitat) and on whether selection exerted by antagonists conflicts with selection exerted by mutualists. Because most mutualisms are vulnerable to exploitation by antagonists, and the distributions of antagonists are unlikely to overlap completely with mutualists, we believe that such a source–sink perspective will be useful for examining the evolution and persistence of mutualisms.