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Abstract When herbivorous insects interact, they can increase or decrease each other's fitness. As it stands, we know little of what causes this variation. Classic competition theory predicts that competition will increase with niche overlap and population density. And classic hypotheses of herbivorous insect diversification predict that diet specialists will be superior competitors to generalists. Here, we test these predictions using phylogenetic meta‐analysis. We estimate the effects of diet breadth, population density and proxies of niche overlap: phylogenetic relatedness, physical proximity and feeding‐guild membership. As predicted, we find that competition between herbivorous insects increases with population density as well as phylogenetic and physical proximity. Contrary to predictions, competition tends to be stronger between than within feeding guilds and affects specialists as much as generalists. This is the first statistical evidence that niche overlap increases competition between herbivorous insects. However, niche overlap is not everything; complex feeding guild effects indicate important indirect interactions.
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This content will become publicly available on February 19, 2026
What Is a Specialist? Quantifying Host Breadth Enables Impact Prediction for Invasive Herbivores
Herbivores are commonly classified as host specialists or generalists for various purposes, yet the definitions of these terms, and their intermediates, are often imprecise and ambiguous. We quantified host breadth for 240 non‐native, tree‐feeding insects in North America using phylogenetic diversity. We demonstrated that a partitioning of host breadth: (1) causes 67% of non‐native insects to shift from a generalist to specialist category, (2) displays a reduction in host breadth from the native to introduced range, (3) identifies an inflection point in a model predicting the likelihood of non‐native insect ecological impact, with a corresponding change in behaviour associated with specialists versus generalists, and (4) enables three models for strong prediction of whether a non‐native forest insect will cause high impacts. Together, these results highlight the primacy of how herbivore host recognition and plant defenses mediate whether novel host interactions will result in high impact after invasion.
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- Award ID(s):
- 2224545
- PAR ID:
- 10659473
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 28
- Issue:
- 2
- ISSN:
- 1461-023X
- Subject(s) / Keyword(s):
- Evolutionary history generalists vs. specialists herbivores invasion risk assessment phylogenetic diversity
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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