Non‐native tree pests have a broader host range than native pests and differentially impact host lineages

Abstract

Abstract Non‐native pests in North America are a growing threat to native trees and forest communities. Theory suggests that a less specialised niche, as reflected by a pest's broad host range, may facilitate successful pest invasions. Incorporating a pest's host range characteristics along with life‐history traits may thus help us better predict future invasions and impacts. We quantified the host range of North American tree pests using indices of host taxonomic richness and the standard effect size of the mean pairwise distance between hosts, then compared the host ranges of non‐native and native pests. We next examined whether non‐native and native pests tended to be associated with phylogenetically distinct sets of host tree lineages. Finally, we evaluated whether pest impacts were associated with pest host ranges, nativity or pest type (i.e. insect vs. pathogen). We found that the set of tree hosts impacted by non‐native pests was phylogenetically distinct from hosts of native pests, and that non‐native insect pests had significantly broader host ranges than native insect pests, perhaps due to an innate ability to associate with diverse tree species. We also found that pathogens generally had broader host ranges than insect pests—possibly a result of more frequent host range expansion. While severity was not associated with pest nativity per se, non‐native pathogens had the greatest impact on their hosts across all pest subsets. Synthesis. We identified important differences in the host ranges of native and non‐native pests, with non‐native pests associated with a broader range of hosts, and this difference was most evident in comparisons between insect pests. We suggest a broad host range might facilitate non‐native pest establishment. We also highlight the need for further research on pest life histories and impacts to better understand the consequences of pest invasions.