Environmental heterogeneity influences species distributions as well as population dynamics within species. Effects of the environment can be both direct and indirect, altering the outcome of biotic interactions. Although it is well known that biotic interactions may strongly affect several vital rates, few studies have investigated how the effect of biotic interactions on life-time fitness and population dynamics depends on environmental context. We studied how the effect of pre-dispersal seed predation on host plant population growth rates varied with soil conditions and vegetation height, monitoring 24 populations of the perennial herb Primula farinosa during three consecutive years. First, we investigated how reductions in population growth rate due to seed predators were related to predation intensity and the sensitivity of population growth rate to predation, respectively. Second, we examined how predation intensity and sensitivity were related to environmental context in terms of soil depth, soil moisture, soil nutrient composition and vegetation height. Both seed predation intensity and sensitivity of population growth rate to seed predation varied considerably among populations, and both contributed to variation in the effects of seed predation on population growth rate. Soil moisture influenced population growth rate in three different ways; via direct effects on potential growth rate, via effects on predation intensity and via effects on the sensitivity of population growth rates to seed predation. We conclude that, in our study system, environmental context influences how biotic interactions affect population dynamics, and that a given environmental parameter can influence population growth rate in different directions through effects on potential growth rate, intensity of biotic interactions, and the sensitivity of population growth rate to these biotic interactions.