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Meta‐analysis is increasingly used in ecology and evolutionary biology. Yet, in these fields this technique has an important limitation: phylogenetic non‐independence exists among taxa, violating the statistical assumptions underlying traditional meta‐analytic models. Recently, meta‐analytical techniques incorporating phylogenetic information have been developed to address this issue. However, no syntheses have evaluated how often including phylogenetic information changes meta‐analytic results. To address this gap, we built phylogenies for and re‐analysed 30 published meta‐analyses, comparing results for traditional vs. phylogenetic approaches and assessing which characteristics of phylogenies best explained changes in meta‐analytic results and relative model fit. Accounting for phylogeny significantly changed estimates of the overall pooled effect size in 47% of datasets for fixed‐effects analyses and 7% of datasets for random‐effects analyses. Accounting for phylogeny also changed whether those effect sizes were significantly different from zero in 23 and 40% of our datasets (for fixed‐ and random‐effects models, respectively). Across datasets, decreases in pooled effect size magnitudes after incorporating phylogenetic information were associated with larger phylogenies and those with stronger phylogenetic signal. We conclude that incorporating phylogenetic information in ecological meta‐analyses is important, and we provide practical recommendations for doing so.

Summary 1.Invasive plants often have novel biotic interactions in their introduced ranges. These interactions, including less frequent herbivore attacks, may convey a competitive advantage over native plants. Invasive plants may vary in defence strategies (resistance vs. tolerance) or in response to the type of herbivore (generalists vs. specialists), but no study to date has examined this broad set of traits simultaneously. 2. Here, we examined resistance and tolerance of Chinese tallow (Triadica sebifera) populations from the introduced and native ranges to generalist (Cnidocampa flavescens) and specialist herbivores (Gadirtha inexacta) in the native range. 3. In a field common-garden test of resistance, caterpillars of each species were raised on plants from native and invasive populations. We found the specialist grew larger on and consumed more mass of invasive plant populations than native populations, while the generalist showed the same performance between them. The results were consistent with our laboratory bioassay using excised leaves. Chemical analyses showed that the invasive plants had lower tannin content and higher ratio of carbohydrate to protein than those of their native counterparts, suggesting that plants from invasive populations have altered chemistry that has a larger impact on specialist than on generalist resistance. 4. To test for differences in herbivore tolerance, plants were first defoliated by specialist or generalist herbivory and then allowed to regrow for 100 days in a field common garden. We found that plants from invasive populations had greater herbivore tolerance than native populations, especially for tolerance to generalists. They also grew more rapidly than native counterparts in the absence of herbivory. 5. Synthesis. The results of these experiments indicate that differences in selective pressures between ranges have caused dramatic reductions in resistance to specialist herbivores and those changes in plant secondary chemistry likely underlie these differences. The greater tolerance of invasive populations to herbivory appears to at least partly reflect an increase in growth rate in the introduced range. The greater tolerance to generalist herbivores suggests the intriguing possibility of selection for traits that allow plants to tolerate generalist herbivores more than specialist herbivores.

Plant-associated soil microbes are important mediators of plant defence responses to diverse above-ground pathogen and insect challengers. For example, closely related strains of beneficial rhizosphere Pseudomonas spp. can induce systemic resistance (ISR), systemic susceptibility (ISS) or neither against the bacterial foliar pathogen Pseudomonas syringae pv. tomato DC3000 (Pto DC3000). Using a model system composed of root-associated Pseudomonas spp. strains, the foliar pathogen Pto DC3000 and the herbivore Trichoplusia ni (cabbage looper), we found that rhizosphere-associated Pseudomonas spp. that induce either ISS and ISR against Pto DC3000 all increased resistance to herbivory by T. ni. We found that resistance to T. ni and resistance to Pto DC3000 are quantitative metrics of the jasmonic acid (JA)/salicylic acid (SA) trade-off and distinct strains of rhizosphere-associated Pseudomonas spp. have distinct effects on the JA/SA trade-off. Using genetic analysis and transcriptional profiling, we provide evidence that treatment of Arabidopsis with Pseudomonas sp. CH267, which induces ISS against bacterial pathogens, tips the JA/SA trade-off towards JA-dependent defences against herbivores at the cost of a subset of SA-mediated defences against bacterial pathogens. In contrast, treatment of Arabidopsis with the ISR strain Pseudomonas sp. WCS417 disrupts JA/SA antagonism and simultaneously primes plants for both JA- and SA-mediated defences. Our findings show that ISS against the bacterial foliar pathogens triggered by Pseudomonas sp. CH267, which is a seemingly deleterious phenotype, may in fact be an adaptive consequence of increased resistance to herbivory. Our work shows that pleiotropic effects of microbiome modulation of plant defences are important to consider when using microbes to modify plant traits in agriculture.

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