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1. Invaders responded more positively to soil biota than native or noninvasive introduced species, consistent with enemy escape

   https://doi.org/10.17605/OSF.IO/P7WVQ  

   Liu, Yu; Zheng, Yu-Long; Jahn, Lydia V.; Burns, Jean H. (January 2021, OSF)

   Understanding the mechanisms governing biological invasions has implications for population dynamics, biodiversity, and community assembly. The enemy escape hypothesis posits that escape from enemies such as herbivores and predators that were limiting in the native range helps explain rapid spread in the introduced range. While the enemy escape hypothesis has been widely tested aboveground, data limitations have prevented comparisons of below- ground mechanisms for invasive and noninvasive introduced species, which limits our understanding of why only some introduced species become invasive. We assessed the role of soil biota in driving plant invasions in a phylogenetic meta−analysis, incorpo- rating phylogeny in the error structure of the models, and comparing live and sterilized conditioned soils. We found 29 studies and 396 effect size estimates across 103 species that compared live and sterilized soils. We found general positive effects of soil biota for plants (0.099, 95% CI 0.0266, 0.1714), consistent with a role of soil mutualists. The effect size of soil biota among invaders was 3.2× higher than for natives, the strength of effects was weaker for older conditioning species with a longer introduced history, and enemy escape was stronger for distant relatives. In addition, invasive species had a weaker allocation tradeoff than natives. By demonstrating that the net effect of soil biota is more positive for invasive than native and noninvasive introduced species, weakens over time since introduction, and strengthens as phy- logenetic distance increasing, we provide mechanistic insights into the considerable role of soil biota in bio- logical invasions, consistent with the predictions of the enemy escape hypothesis. 

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2. Synergistic effects of canopy chemistry and autogenic soil biota on a global invader

   https://doi.org/10.1111/1365-2745.14113  

   Majumdar, Sudipto; Kaur, Harleen; Rinella, Matthew J.; Kundu, Anish; Vadassery, Jyothilakshmi; Erbilgin, Nadir; Callaway, Ragan M.; Cadotte, Marc W.; Inderjit (July 2023, Journal of Ecology)

   Abstract Soil biota have strong effects on plants, but we have a poor understanding of how plant chemistry might modify these effects. We examined the effect of soil biota associated with an exotic invasive tree,Prosopis juliflora, versus that associated with native species, from seven sites across India on conspecifics and two other plant species. We then measured changes in species‐specific soil biota effects (identified as plant–soil feedbacks, PSFs) when leaf leachate fromP. julifloraor from native plant species was added to soil containing respective live and sterile soil inoculum.We quantified the amino acid L‐tryptophan from leaf leachate ofP. juliflora,Leucaena leucocephala(another invader), and two native species. We also tested effects ofP. julifloraor native species soil inoculum amendment of tryptophan onP. juliflora,P. cinerariaandL. leucocephalaacross seven sites. We then quantified the microbially metabolized derivatives of tryptophan, phytohormone indole‐3‐acetic acid (IAA) and intermediates after adding tryptophan intoP. julifloraand native soils.Soil biota associated withP. julifloragenerated positive effects on conspecifics andL. leucocephala, but negative effects on the native congenerP. cineraria. WhenP. julifloraleaf leachate was added to soil with liveP. juliflorainoculum, PSFs became more positive forP. julifloraand other species, compared to leaf leachate amended with sterile soil inoculum. Native leaf leachate interacted weakly with soil biota to impact biomass of conspecifics and heterospecifics.There was roughly 10× more tryptophan in the leaf leachate ofP. juliflorathan in the leaf leachate of other species. Tryptophan generally increased positive PSFs associated withP. juliflorarelative to soil biota associated with other plant species. When tryptophan was added to liveP. juliflorasoil, IAA and its intermediates were produced at five of seven sites, and at four of these sites soil biota fromP. juliflorahad positive PSFs.Synthesis. These results provide the first experimental evidence that a chemical leached from the leaves of an invader regulates PSFs. Our results indicate that canopy effects and PSFs, which are usually studied independently, can interact in ways that strongly affect conspecifics and neighbouring species. 

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3. Global test of the enemy release hypothesis reveals similar patterns of herbivory across native and non-native plants

   https://doi.org/10.1101/2024.10.21.619365  

   Galmán, Andrea; Hahn, Philip G; Inouye, Brian D; Underwood, Nora; Liu, Yanjie; Whitehead, Susan R; Wetzel, William C (October 2024, bioRxiv)

   The Enemy Release Hypothesis (ERH) proposes that non-native plants escape their co-evolved herbivores and benefit from reduced herbivory in their introduced ranges. Numerous studies have tested this hypothesis, with conflicting results, but previous studies focus on average levels of herbivory and overlook the substantial within-population variability in herbivory, which may provide unique insights into the ERH. We tested differences in mean herbivory and added a novel approach to the ERH by comparing within-population variability in herbivory between native and non-native plant populations. We include several covariates that might mask an effect of enemy release, including latitude, regional plant richness, plant growth form and plant cover. We use leaf herbivory data collected by the Herbivory Variability Network for 788 plant populations (616 native range populations and 172 introduced range populations) of 503 different native and non-native species distributed worldwide. We found no overall differences in mean herbivory or herbivory variability between native and non-native plant populations. Taken together, our results indicate no evidence of enemy release for non-native plants, suggesting that enemy release is not a generalized mechanism favoring the success of non-native species. 

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4. Reciprocal human-natural system feedback loops within the invasion process

   https://doi.org/10.3897/neobiota.62.52664  

   Sinclair, James S.; Brown, Jeffrey A.; Lockwood, Julie L. (October 2020, NeoBiota)

   null (Ed.)

   Biological invasions are inextricably linked to how people collect, move, interact with and perceive non-native species. However, invasion frameworks generally do not consider reciprocal interactions between non-native species and people. Non-native species can shape human actions via beneficial or detrimental ecological and socioeconomic effects and people, in turn, shape invasions through their movements, behaviour and how they respond to the collection, transport, introduction and spread of non-natives. The feedbacks that stem from this ‘coupled human and natural system’ (CHANS) could therefore play a key role in mitigating (i.e. negative feedback loops) or exacerbating (i.e. positive feedback loops) ongoing and future invasions. We posit that the invasion process could be subdivided into three CHANS that span from the source region from which non-natives originate to the recipient region in which they establish and spread. We also provide specific examples of feedback loops that occur within each CHANS that have either reduced or facilitated new introductions and spread of established non-native species. In so doing, we add to exisiting invasion frameworks to generate new hypotheses about human-based drivers of biological invasions and further efforts to determine how ecological outcomes feed back into human actions. 

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5. Nonnative tree invaders lead to declines in native tree species richness

   https://doi.org/10.1073/pnas.2424908122  

   Liu, Yunpeng; Scheiner, Samuel M; Hogan, J Aaron; Thomas, Matthew B; Soltis, Pamela S; Guralnick, Robert P; Soltis, Douglas E; Lichstein, Jeremy W (April 2025, Proceedings of the National Academy of Sciences)

   Biological invasions are profoundly altering Earth’s ecosystems, but generalities about the effects of nonnative species on the diversity and productivity of native communities have been elusive. This lack of generality may reflect the limited spatial and temporal extents of most previous studies. Using >5 million tree measurements across eastern US forests from 1995 to 2023, we quantified temporal trends in tree diversity and biomass. We then analyzed community-level changes in native tree diversity and biomass in relation to nonnative tree invasion and native species colonization. Across the entire eastern United States, native tree species richness decreased over time in plots where nonnatives occurred, whereas nonnative species richness and the biomass of both natives and nonnatives increased over time. At the community scale, native richness tended to decline following nonnative invasion, whereas native biomass and richness-independent measures of trait and phylogenetic diversity tended to remain stable. These patterns can be explained by the rarity of the displaced native species and their functional and phylogenetic similarity to native species that survived nonnative invasions. In contrast, native survivors tended to be functionally distinct from nonnative invaders, suggesting an important role for niche partitioning in community dynamics. Colonization by previously absent native species was associated with an increase in native richness (beyond the addition of native colonizers), which contrasts with declines in native richness that tended to follow nonnative invasion. These results suggest a causal role for nonnative species in the native richness decline of invaded communities. 

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