Evidence of publication bias
More negative effects of stressors in studies with lower precision suggest that 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 S8). We thus adjusted meta-analytic estimates for analyses in Q1 and Q2 by including variance as an additional moderator in both models.
Some results in Q1 differed qualitatively after adjusting for small study effects. Specifically, effects of endogenous environmental stressors and pollution became non-significant when variance was included as a moderator (Table S9; Fig. S9). 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 few studies (n = 8).
In Q2, our qualitative results remained essentially unchanged after adjusting for publication bias. Overall, effects of endogenous environmental stressors reduced host survival and increased both infectivity traits (Table S10; Fig. S10). 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 S10). Finally, the negative impact of chemical pollution on host survival and prevalence in our primary analysis (Table S5; Fig. 3) became indistinguishable from zero in the adjusted model (Table S10; Fig. S10). However, we caution that this result was based on a relatively small number of experiments (n = 9).