Abstract
A long‐standing goal of invasion biology is to identify factors driving highly variable impacts of non‐native species. Although hypotheses exist that emphasize the role of evolutionary history (e.g., enemy release hypothesis & defense‐free space hypothesis), predicting the impact of non‐native herbivorous insects has eluded scientists for over a century.Using a census of all 58 non‐native conifer‐specialist insects in North America, we quantified the contribution of over 25 factors that could affect the impact they have on their novel hosts, including insect traits (fecundity, voltinism, native range, etc.), host traits (shade tolerance, growth rate, wood density, etc.), and evolutionary relationships (between native and novel hosts and insects).We discovered that divergence times between native and novel hosts, the shade and drought tolerance of the novel host, and the presence of a coevolved congener on a shared host, were more predictive of impact than the traits of the invading insect. These factors built upon each other to strengthen our ability to predict the risk of a non‐native insect becoming invasive. This research is the first to empirically support historically assumed hypotheses about the importance of evolutionary history as a major driver of impact of non‐native herbivorous insects.Our novel, integrated model predicts whether a non‐native insect not yet present in North America will have a one in 6.5 to a one in 2,858 chance of causing widespread mortality of a conifer species if established (R 2 = 0.91) Synthesis and applications. With this advancement, the risk to other conifer host species and regions can be assessed, and regulatory and pest management efforts can be more efficiently prioritized.
Highlights
Expansion of global trade has increased establishment of non‐na‐ tive herbivorous insects (Aukema et al, 2010), most of which cause a little impact in their invaded range (Williamson & Fitter, 1996)
We discovered that divergence times between native and novel hosts, the shade and drought tolerance of the novel host, and the presence of a coevolved
We tested the hypothesis that multiple traits better predict high‐impact invasions by focusing on non‐native insect herbivores in North America that specialize on coniferous (Order Pinales) trees, which are widely distributed across latitude and elevation, dominate multiple biomes, are well studied, and have great ecological and economic value (Eckenwalder, 2009)
Summary
Expansion of global trade has increased establishment of non‐na‐ tive herbivorous insects (Aukema et al, 2010), most of which cause a little impact in their invaded range (Williamson & Fitter, 1996). The success of some classical biological control programs provides empirical support for the enemy re‐ lease hypothesis (DeBach & Rosen, 1991), and a lack of coevolved defenses against some invasive herbivorous insects has been doc‐ umented (Brooks, Ervin, Varone, & Logarzo, 2012; Desurmont, Donoghue, Clement, & Agrawal, 2011; Woodard, Ervin, & Marsico, 2012), these hypotheses have not been applied to predict the im‐ pact of non‐native insects. We tested the hypothesis that multiple traits better predict high‐impact invasions by focusing on non‐native insect herbivores in North America that specialize on coniferous (Order Pinales) trees (hereafter, conifer specialists), which are widely distributed across latitude and elevation, dominate multiple biomes, are well studied, and have great ecological and economic value (Eckenwalder, 2009). Our research is the first to generate quantitative evidence for the role of evolutionary history as a predictor of the impact of non‐native insect herbivores on their host plants
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