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).