Consequences of novel plant-insect interactions: A meta-analysis of Lepidoptera and exotic host plants
Investigating the effects of invasion on native biodiversity is one of the most pressing challenges in ecology. As humans have colonized the planet, the number of species that have been introduced to new ecosystems has increased tremendously. These introductions, while often detrimental to global biodiversity, provide novel opportunities to study species interactions. Our goal in this study was to quantify the overall effects of invasive plant species on butterfly and moth communities. In addition, we sought to elucidate the fitness consequences of non-native hosts on native lepidopterans. We conducted a meta-analysis on a total of 34 papers representing 81 experiments: 34 lepidopteran performance studies, 14 oviposition preference studies, 13 survival studies, 12 community abundance studies, and 8 community richness studies. To assess the generality of the response of lepidopteran species and communities to invasion by exotic plants, we calculated effect sizes for each study and estimated the distribution of the true effect size using a hierarchical Bayesian model for (1) lepidopteran species richness, (2) abundance, (3) larval performance, and (4) larval survival. In addition, we estimated the probability of publication bias, in terms of the probability that non-significant results were not selected for publication, for each of the response variables.
We found that larvae overwhelmingly performed worse on exotic hosts and suffered reduced survival rates. In addition, alien plant invasion reduced the overall abundance and richness of lepidopteran communities. We did not find a significant relationship between oviposition preference and host origin. No publication bias was detected for any of the response variables. Reduced abundance of moth and butterfly larvae may have trophic effects on insectivores, particularly birds. Several mechanisms by which invasive plants may reduce lepidopteran abundance have been suggested, including crowding out of native hosts, changing plant architecture by forming dense thickets that are not conducive to basking or feeding, and facilitating invasive pests. Our results suggest that exotic plant species may be a threat to native insect biodiversity due to their role as ecological traps. Assuming that native hosts are still extant and accessible, invasive plants should be eradicated from habitat patches in order to mitigate severe reductions in insect abundances, especially for the most specialized insects. However, as landscapes become highly altered by anthropogenic change, it may be the case that weeds will be the only hosts widely available. This may explain why we see widespread utilization of exotic hosts in highly disturbed and modified areas.