Figure 5

The effect of augmentative releases of predators on (a) foliar-foraging predator abundance, (b) ground-dwelling predator abundance, and (c) parasitoid abundance in landscapes of varying complexity. Predicted responses for the control (solid lines) and augmentative releases (dashed lines) treatments are calculated from the set of best supported linear and generalized mixed-effects models (lme4). Effects of the interactions between treatment and landscape complexity were significant (P < 0.05) for foliar-foraging predators and parasitoid abundance. In the top Figures (a–c) every point represents the mean treatment value in a given experimental plot for a given sampling period (i.e. 22 experimental plots and 3 sampling periods). The bottom figs. (d–f) are effect sizes (mean ± 95% CI) for foliar predators (d), ground predators(e), and parasitoid abundance (f) based on the difference in the marginal means between plots with and without predator releases across the landscape complexity gradient. A positive effect size indicates higher abundance of natural enemies in predator compared to control plots, while a negative effect size indicates lower abundance of natural enemies in predator plots. Pairwise comparisons were individually calculated at even intervals across the landscape complexity gradient. Asterisks denote effect sizes that are significantly different from zero (P < 0.05). Summary statistics of the LMER and GLMER models used to estimate marginal means and confidence intervals are available in Table 1.