Evidence of publication bias
More negative effects of stressors in studies with lower precision suggested publication bias may partially explain our results for both Q1 and Q2 (Fig. 4). We confirmed these negative relationships between effect size and precision using a two-step modified Egger’s test (Table S5). We thus adjusted meta-analytic estimates for the analyses in Q1 and Q2 by including variance as an additional moderator in both models.
Some of our results in Q1 differed qualitatively after adjusting for small study effects. Specifically, the effects of endogenous environmental stressors and pollution became non-significant when variance was included as a moderator (Table S6; Fig. S4). Moreover, the effect of resource limitation on survivorship changed direction after the small-study adjustment. However, we note that this effect was indistinguishable from zero in both unadjusted and adjusted models and was based on a few studies (n = 8).
In Q2, our qualitative results remained largely unchanged after adjusting for publication bias. Overall, the effects of endogenous environmental stressors reduced host survival and increased both infectivity traits (Table S7; Fig. S5). As in our primary analysis, resource limitation in the adjusted model negatively affected fecundity, but the meta-analytic effect on intensity was marginally non-significant (Table S7). Finally, adjusting for small-study effects revealed that the negative effects of chemical pollution on host survival and prevalence found in our primary analysis (Table S4; Fig. 3) became indistinguishable from zero in the adjusted model (Table S7; Fig. S5). However, we caution that this result was based on a relatively small number of experiments (n = 9).