Environmental context influences both the intensity of seed predation and plant demographic sensitivity to attack.

Variation in mutualistic and antagonistic interactions are important sources of variation in population dynamics and natural selection. Environmental heterogeneity can influence the outcome of interactions by affecting the intensity of interactions, but also by affecting the demography of the populations involved. However, little is known about the relative importance of environmental effects on interaction intensities and demographic sensitivity for variation in population growth rates. We investigated how soil depth, soil moisture, soil nutrient composition, and vegetation height influenced the intensity of seed prédation as well as host plant demography and sensitivity to seed prédation in the perennial herb Primula farinosa. Intensity of seed prédation ranged from 0% to 80% of seeds damaged among the 24 study populations and was related to soil moisture in two of four years. The effect of seed prédation on plant population growth rate (λ) ranged from negligible to a reduction in X by 0.70. Sensitivity of population growth rate to prédation explained as much of the variation in the reductions in population growth rate due to seed prédation as did prédation intensity. Plant population growth rate in the absence of seed prédation and sensitivity to prédation were negatively related to soil depth and soil moisture. Both intensity of prédation and sensitivity to prédation were positively correlated with potential population growth rate and, as a result, there was no significant relationship between prédation intensity and realized population growth rate. We conclude that in our study system environmental context influences the effects of seed prédation on plant fitness and population dynamics in two important ways: through variation in interaction intensity and through sensitivity to the effects of this interaction. Moreover, our results show that a given abiotic factor 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 interactions. [ABSTRACT FROM AUTHOR]