It has been argued that the complexity of interactions among species in communities limits the potential for pair-wise coevolution. There are, however, few studies that have tested specific hypotheses of how other species' interactions influence coevolution between particular species pairs. Red squirrels and red crossbills compete for pine seeds. The investigator will test whether the red squirrels impede the coevolutionary interaction between red crossbills and pines by examining characteristics of seed and cone morphology of lodgepole pine where one or both competitors are present (or absent). This research will extend studies of complex species interactions by determining the evolutionary significance of indirect interactions. Second, it will distinguish among several potential explanations for why pair-wise coevolution may be uncommon. Third, it will distinguish between alternative hypotheses of coevolution. This study will provide an understanding of the impact of various seed predators on geographic variation in an important commercial pine species, lodgepole pine, and will help elucidate the importance of different seed predators on pine evolution and diversity. Second, it will provide the basis for understanding why the absence of species from communities can lead to rapid evolutionary change in the remaining species in these communities. The implications are that introductions of formerly absent species may result in increases of the introduced species to the point where they become pests, may lead to local extinctions of unique species, and may result in the homogenization of formerly unique communities.
