Appendix A.
To evaluate the effect of any bias that multiple data points from a single paper would
impose on the results, we calculated a single effect size for any paper that contained three or
more independent datapoints. Summary meta-analyses were then conducted on each response
variable (e.g. population abundance, individual growth rate, survival and fecundity) in this
reduced dataset (non-toxic prey studies only). All studies where predator growth rate was the
measured response variable contained only a single data point. Therefore, results on predator
growth rate are the same as in the full dataset and not reported here.
Results:
Summary effect & heterogeneity in the effect of non-native prey on native predator population
abundance
The reduced data set contained a total of twenty-seven datapoints (in contrast to 68
datapoints in the full analysis). Summary analysis of the effect size indicated that non-native
prey had a significant positive effect on native predators relative to native prey (Effect size, lnR
= 0.52, df = 26, bootstrap 95% CI = 0.25 – 0.80; Rosenthal’s number 236). Additionally there
was significant heterogeneity in effect sizes (QT = 41.13, df = 26, p = 0.03).
Summary effect & heterogeneity in the effect of non-native prey on native predator fecundity
The reduced data set contained a total of six datapoints (in contrast to 8 datapoints in the
full analysis). Summary analysis of the effect size indicated that non-native prey had a
significant negative effect on native predators relative to native prey (Effect size, lnR = -1.03, df
= 5, 95% bootstrap CI = -1.64 - -0.46; Rosenthal’s number 17). Additionally there was not
significant heterogeneity in effect sizes (QT = 6.31, df = 5, p = 0.28).
Summary effect & heterogeneity in the effect of non-native prey on native predator survival
The reduced data set contained a total of seven datapoints (in contrast to 10 datapoints in
the full analysis). Summary analysis of the effect size indicated that non-native prey had a
similar effect effect on native predators relative to native prey (Effect size, lnR = 0.25, df = 6,
95% bootstrap CI = -0.24 – 1.08). Additionally there was significant heterogeneity in effect sizes
(QT = 41.13, df = 6, p < 0.001).