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opencc-by-3.0-usJun 2021View details →

Invasive tree cover covaries with environmental factors to explain the functional composition of riparian plant communities

Invasive species are a major cause of biodiversity loss worldwide, but their impact on communities and the mechanisms driving those impacts are varied and not well understood. This study employs functional diversity metrics and guilds - suites of species with similar traits - to assess the influence of an invasive tree (Tamarix spp.) on riparian plant communities in the southwestern United States. We asked: 1) What traits define riparian plant guilds in this system? 2) How do the abundances of guilds vary along gradients of Tamarix cover and abiotic conditions? 3) How does the functional diversity of the plant community respond to the gradients of Tamarix cover and abiotic conditions? We found nine distinct guilds primarily defined by reproductive strategy, as well as height, seed weight, specific leaf area, drought and anaerobic tolerance. Guild abundance varied along a covarying gradient of local and regional environmental factors and Tamarix cover. Guilds relying on sexual reproduction, in particular those producing many light seeds over a long period of time were more strongly associated with drier sites and higher Tamarix cover. Tamarix itself appeared to facilitate more shade tolerant species with higher specific leaf areas than would be expected in resource poor environments. Additionally, we found a high degree of specialization (low functional diversity) in the wettest, most flood-prone, lowest Tamarix cover sites as well as in the driest, most stable, highest Tamarix cover sites. These guilds can be used to anticipate plant community response to restoration efforts and in selecting appropriate species for revegetation.

Invasion drives plant diversity loss through competition and ecosystem modification

1. Although invasive plants increasingly contribute to the current biodiversity crisis, the mechanisms through which they impact native communities are still poorly understood. Community ecology theory has emphasized direct competitive displacement over common resources, but invasion-driven ecosystem modifications, such as altered soil pH, might also have consequences for plant diversity. However, the relative importance of ecosystem modification compared to direct resource competition has rarely been tested. 2. Here we studied the invasive vine Vincetoxicum rossicum across invaded meadows in southern Ontario, Canada. In each meadow site, we quantified: 1) the strength of impact on the resident plant community, 2) the potential for competition with resident species (as the degree of niche-dissimilarity and competitive superiority to the residents based on their functional traits), and 3) the amount of ecosystem modification related to invasion. 3. We found that impacts on plant biodiversity were more negative where the invader had greater potential to competitively displace species (because it had a similar niche as the residents or was competitively superior), but also where it strongly altered soil N pools, moisture and pH. 4. Synthesis. Our case study suggests that, while competition is undoubtedly an important driver of invasion impact, ecosystem modifications can have cascading effects on plant communities, thereby magnifying the impacts of biological invasions.

Data from: Latitudinal patterns of alien plant invasions

Latitudinal patterns of biodiversity have long been a central topic in ecology and evolutionary biology. However, while most previous studies have focused on native species, little effort has been devoted to latitudinal patterns of plant invasions (with a few exceptions based on data from sparse locations). Using the most up-to-date worldwide native and alien plant distribution data from 801 regions (including islands), we compared invasion levels (i.e. alien richness/total richness) in the Northern and Southern Hemispheres and across continental regions and islands around the globe. Results from quantile regressions using B-splines to model nonlinearity showed (1) declining richness with increasing latitude, although the highest alien richness occurs at around 40 degrees in both hemispheres, (2) decreasing invasion levels towards higher latitudes on islands but a unimodal pattern in invasion level in continental regions in each hemisphere, (3) significantly higher invasion levels on islands than in continental regions, and (4) a greater variability in invasThrough field observations and published records (e.g., literature search).ion levels on islands at low latitudes than on high-latitude islands. In continental regions, only the mid-latitudes had high variability with both low and high invasion levels. Our findings identified latitudes with invasion hotspots where management is urgently needed, and latitudes with many areas of low invasions but high conservation potential where prevention of future invasions should be the priority.

Data from: Consequences of aboveground invasion by non-native plants into restored vernal pools do not prompt changes in belowground processes

Given the frequent overlap between biological plant invasion and ecological restoration efforts it is important to investigate their interactions to sustain desirable plant communities and modify long-term legacies both above and belowground. To address this relationship, we used natural reference, invaded, and constructed vernal pools in the Central Valley of California to examine potential changes in direct and indirect plant effects on soils associated with biological invasion and active restoration ecosystem disturbances. Our results showed that through a shift in vegetation composition and changes in the plant community tissue chemistry, invasion by non-native plant species has the potential to transform plant inputs to soils in vernal pool systems. In particular, we found that while non-native litter decomposition was driven by seasonal and interannual variability, associated with changes in precipitation, the overall decomposition for non-native litter was drastically lower than native species. This shift has important implications for long-term alterations in plant-based inputs to soils in a negative feedback to nutrient cycling. Moreover, these results were independent of historic active restoration efforts. Despite the consistent shift in plant litter decomposition rates and community composition, we did not detect associated shifts in belowground function associated with invasion by non-native plants. Instead, soil C:N ratios and microbial biomass did not differ between invaded and reference naturally occurring pools but were reduced in the manipulated restored pools independent of invasion levels. Our results suggest that while there is an observed invasive positive feedback aboveground, this trajectory is not necessarily represented belowground and restoration legacies were still dominant ten years after practices were applied. Restoration practices that limit invasive plant feedbacks and account for soil legacy recovery, therefore offer the best solution for disturbed ephemeral ecosystems.

FIGURE 5. CAPS assay for A in Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

FIGURE 5. CAPS assay for A. hydrillicola. RsaI digestion of a PCR-amplified fragment of the16S rRNA gene produces a 247 bp sequence that is diagnostic for the species. At top, the sizes of RsaI digestion products from A. hydrillicola and related cyanobacteria are shown. Lane 1: RsaI digestion products of PCR-amplified DNA from an axenic culture of A. hydrillicola. Lane 2: PCR product from DNA of a field sample. Lane 3: RsaI digestion products of PCR-amplified DNA from a field sample. Arrowheads indicate the size (in base pairs) of the products of PCR and RsaI digestion. M = 100 bp DNA markers. Closed circles = PCR primer binding sites. Open circles = RsaI restriction sites.

FIGURE 1 in Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

FIGURE 1. Locations (in order of confirmation) across the Southeastern United States where Aetokthonos hydrillicola, invasive plants (Hydrilla, Egeria, Myriophyllum), and bird deaths from AVM have been confirmed.

FIGURE 7 in Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

FIGURE 7. Secondary structure of conserved domains in the 16S-23S ITS of true-branching Aetokthonos and Fischerella. A–C. D1–D1' helix, D–F. Box-B helix, G–I. V3 helix.

FIGURE 6 in Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

FIGURE 6. Bayesian Analysis based on alignment of 318 OTU's. Posterior probabilities and bootstrap values from a parsimony analysis of the same alignment are shown above or in close proximity to the nodes that are supported at least at the 50% level. Asterisks (*) indicate 1.00 or 100% support, hyphens (-) indicate unsupported node. Nodes with no support from either analysis have no annotation. The six arrows indicate the clades in the tree consisting of true-branching taxa, and show that the former concept of Stigonematales or Section V

FIGURE 3 in Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

FIGURE 3. Electron Microscope views of Aetokthonos hydrillicola. A–C. Scanning electron microscope views showing dehiscent apical caps (white arrows). D. Cells embedded in firm, thick, mucilage. Dark inclusions are likely cyanophycin bodies. E. Dehiscent apical cell showing initiation of dehiscence. F. Four thylakoids with characteristic electron dense and electron light areas, with dark areas associated with thylakoids representing phycobilisomes. G. Cell showing characteristic thylakoids, arrowed thylakoids shown at greater magnitude in Fig. 3F. H. High magnification views of cyanophycin and polyphosphate bodies.

FIGURE 2 in Aetokthonos hydrillicola gen. et sp. nov.: Epiphytic cyanobacteria on invasive aquatic plants implicated in Avian Vacuolar Myelinopathy

FIGURE 2. Light microscope views of Aetokthonos hydrillicola. A. Fluorescence microscopy of A. hydrillicola on leaf of Hydrilla, scale = 100 μm. B. Fluorescence microscopy of thallus morphology in culture, scale = 100 μm. C–D. Fluorescence microscopy of branching filaments, arrows show hormogonia production in sheath, Scale = 10 μm. E. Thallus showing apical caps (black arrow) and thick-walled enlarged cells possibly functioning as akinetes (white arrow), scale = 10 μm. F–G. Thallus showing typical branching pattern and dehiscent apical cells (hormocytes?) (arrows), scale=10 μm.

Morrison deer and invasive plants in suburban forests 2021 Ecoscience

Fragmented suburban forests of the northeastern US are challenged by abundant white-tailed deer and nonindigenous plant invasions. Deer browsing/grazing pressure varies among sites, potentially affecting herbivory on nonindigenous plants and their invasion success. We aimed to identify a useful deer pressure indicator for suburban forests and then use it to relate deer pressure to grazing on and abundance of two herbaceous invaders, Microstegum viminuem and Alliaria petiolata. We compared three indicators: fecal pellet accumulation rate, deer browse on indigenous woody plants, and indigenous shrub layer cover. The pellet method produced estimates generally far below the region's known deer density. Browse rates and shrub layer cover were negatively correlated, and correlations of the three indicators with evidence of deer pressure from a subsequent 6.5-year exclosure experiment supported shrub layer cover as the better choice. Using that measure in ten forests, we detected a weak pattern of more grazed stands under greater deer pressure, but few plants per stand were grazed; any negative influence of deer on these species was limited to individuals, without population effects. Alliaria petiolata abundance was unrelated to deer pressure, but M. vimineum abundance was greater in forests with more deer pressure, suggesting facilitation of its invasion.

opencc-by-4.0Jul 2021View details →

Data and code for "Insect and plant invasions follow two waves of globalization"

Data and code for "Insect and plant invasions follow two waves of globalization", Ecology Letters

opencc-by-4.0Aug 2021View details →

Data and code for "Insect and plant invasions follow two waves of globalization"

Data and code from: Bonnamour, A., Gippet, J.M.W.& Bertelsmeier, C. (2021) Insect and plant invasions follow two waves of globalisation. Ecology Letters, 24, 2418–2426. <a href="https://doi.org/10.1111/ele.13863">https://doi.org/10.1111/ele.13863</a>

opencc-zeroSep 2021View details →

Magnitude and timing of resource pulses interact to affect plant invasion

Human activities can cause resource fluctuations through reducing uptake by the resident vegetation (e.g., disturbance) or through changing external resource supply (e.g., fertilization). Resource fluctuations often occur as pulses which are low frequency, large magnitude and short duration, and now are recognized as an important driver of plant invasions. However, resource pulses often vary dramatically in a number of attributes, yet how these attributes mediate the impacts of resource pulses on plant invasions remains unclear. Erigeron canadensis is a serious invader of disturbed habitats and agricultural fields in China. Thus, it experiences nutrient pulses with different magnitudes and timings. Here, we grew E. canadensis and six co-occurring native plant species with three different magnitudes of nutrient enrichment (low, medium or high). For each magnitude, we added equivalent amounts of nutrients with a constant supply as a control or one of three pulses with different timings (early, middle or late stages). We found that pulse magnitude, timing and their interaction significantly affected E. canadensis growth (biomass production) and invasion (proportion of biomass in a pot). For each timing, E. candensis growth and invasion increased with nutrient magnitude. At low magnitude, middle and late pulses promoted E. canadensis growth and invasion. At medium magnitude, late pulses suppressed E. canadensis growth, but did not affect its invasion. At high magnitude, early and middle pulses strongly suppressed E. canadensis growth and invasion. In contrast, natives generally exhibited different responses to nutrient pulses. Our study shows that plant responses are not just dependent on the presence of a resource pulse but also on its attributes. In contrast to theory and many empirical studies, our results show that resource fluctuation does not always promote plant invasion. We highlight that the attributes of resource pulses are key to understanding the impact of resource fluctuations on plant invasion.

opencc-zeroOct 2021View details →

Current and future plant invasions in protected areas: Does clonality matter?

Aim: Protected areas (PAs) play an important role in biodiversity conservation, but remain increasingly threatened by invasive alien plant species (IAPS) in conjunction with global climate change. The latter is modifying the distribution of the former, and the magnitude and direction of distributional changes are predicted to vary depending on species dispersal mode. Here we address the question of whether clonality is expected to affect the future invasion pattern in PAs. Location: World-wide. Time period: 1950–2100. Major taxa studied: 36 invasive alien plant species Methods: We used ensembles of three species distribution models (GLM, GAM and Maxent) based on > 70,000 occurrence records to project the distribution of 36 of the world's most invasive clonal and non-clonal plants in > 20,000 PAs. Projections were based on three greenhouse gas concentration scenarios (low, medium and high) for 2080. Results: Climate change showed little impact on the global invasion pattern in PAs and clonality showed little effect when all biomes were processed in concert. However, we discerned that the future invasion risk of clonal IAPS markedly increased in biomes located at high elevation and high latitude compared to non-clonal IAPS, while the risk decreased in lower-elevation tropical and subtropical biomes where asexual reproduction may be a less successful trait. We also showed that invasion hotspots overlapped with biodiversity hotspots and two realms (i.e., Nearctic and Palearctic), which calls for bridging the gap between invasion and conservation sciences and for more concerted management strategies. Main conclusions: We suggest that effective management of IAPS in PAs should consider in which biomes PAs are located as well as the reproductive traits of IAPS that are present or may become so.

Supplementary material 5 from: Bowman EA, Plowes RM, Gilbert LE (2023) Evidence of plant-soil feedback in South Texas grasslands associated with invasive Guinea grass. NeoBiota 81: 33-51. https://doi.org/10.3897/neobiota.81.86672

Results of t-test examining differences in soil characteristics between invaded and uninvaded sites. Electrical conductivity, phosphorus, and sulfur were log-transformed prior to analysis.

Supplementary material 4 from: Bowman EA, Plowes RM, Gilbert LE (2023) Evidence of plant-soil feedback in South Texas grasslands associated with invasive Guinea grass. NeoBiota 81: 33-51. https://doi.org/10.3897/neobiota.81.86672

Results of one-way ANOVA examining the effect of autoclave time on soil characteristics. Electrical conductivity, phosphorus, and sulfur were log-transformed prior to analysis.

Supplementary material 1 from: Bowman EA, Plowes RM, Gilbert LE (2023) Evidence of plant-soil feedback in South Texas grasslands associated with invasive Guinea grass. NeoBiota 81: 33-51. https://doi.org/10.3897/neobiota.81.86672

Soil sampling sites showing extent of Guinea grass patch (white boundary, I) and adjacent uninvaded grassland (N) with nearby mesquite tree mottes. Google Earth Imagery date 1/13/2014. Scale bar 70m.

Supplementary material 2 from: Bowman EA, Plowes RM, Gilbert LE (2023) Evidence of plant-soil feedback in South Texas grasslands associated with invasive Guinea grass. NeoBiota 81: 33-51. https://doi.org/10.3897/neobiota.81.86672

Initial germination of Guinea grass seed (a) and the seedbank (b) during week 1 was higher in soil from invaded sites than uninvaded sites. All data shown here are non-transformed.

Supplementary material 3 from: Bowman EA, Plowes RM, Gilbert LE (2023) Evidence of plant-soil feedback in South Texas grasslands associated with invasive Guinea grass. NeoBiota 81: 33-51. https://doi.org/10.3897/neobiota.81.86672

Effect of soil handling method on Guinea grass seedling count (a), native community plant abundance (b), and native community biomass (c). MSS: mixed soil sampling; ISS: individual soil sampling. All data shown are non-transformed.