Trait divergence in resource use and susceptibility to predation can promote local competitor coexistence if such divergence generates demographic advantages when species are rare, producing frequency-dependent stabilizing effects. These effects may vary spatially as populations experience different ecological conditions shaping species interactions. Here, we examine how population-specific differences in competitive and predator–prey interactions among damselfly larvae are associated with variation in the strength and occurrence of stabilizing mechanisms underlying coexistence. Using field transplant experiments, we compared growth and mortality rates between local and transplanted damselfly populations to assess whether stabilizing effects differed across population–environment contexts. We observed population-specific differences in growth rates in one species, but found no evidence that resource competition generated stabilizing effects. By contrast, fish predation imposed strong frequency-dependent mortality generating stabilization, and the occurrence and magnitude of this effect differed between local and non-local populations. However, the direction and strength of these differences varied between species: in one species, frequency-dependent predation effects were marginally reduced, whereas in the other they were effectively absent. These asymmetries suggest that population-specific responses to predators, potentially driven by local adaptation, may influence coexistence outcomes, even under similar ecological settings. A laboratory experiment revealed no differences in predation rates imposed by fish on local versus non-local damselfly prey, indicating that observed field patterns are unlikely to arise from predator local adaptation to prey alone. Collectively, our results highlight how spatial variation in species interactions can generate heterogeneity in stabilizing processes, while underscoring the challenges of disentangling ecological and evolutionary mechanisms in natural systems.