Determining the adaptive significance of plant secondary metabolites requires studies that examine the allocation of chemical compounds across space and time, as well as the effects on ecological interactions surrounding plants. Although secondary metabolites have been primarily studied in leaves, many fruits contain complex mixtures of secondary metabolites that could play key roles in mediating interactions with both mutualists and antagonists. We used ecological field experiments in combination with analytical chemistry to document (1) variation in interactions with seed dispersers and seed predators across space and time and (2) how intraspecific variation in chemical traits of seeds and elaiosomes (seed appendages that attract seed-dispersing ants) of Sanguinaria canadensis (Papaveraceae) mediates this variation. Across space, we found that although the activity of seed-dispersing ants increased with elevation, rates of seed dispersal did not, suggesting that changes in fruit chemical and morphological traits make higher elevation fruits relatively less attractive. Moreover, throughout fruit development, ant preferences for seeds first decreased before strongly increasing to fruit maturity. Such effects were not driven by changes in seed morphology or the total concentrations of nutrients (fatty acids) or defense compounds (alkaloids) in elaiosomes, but rather jointly driven by changes in the composition of fatty acids and alkaloids. In contrast, the preferences of seed predators did not change throughout fruit development. Overall, these results demonstrate that changes in fruit chemical traits across space and time can play a key, yet variable, role in mediating interactions with mutualistic and antagonistic fruit consumers. By documenting intraspecific variation in allocation patterns of plant nutrients and secondary metabolites, this research provides insight into the evolutionary ecology of plant chemical traits.