More Like this

1. Macroscale analyses suggest invasive plant impacts depend more on the composition of invading plants than on environmental context

   https://doi.org/10.1111/geb.13749  

   Beaury, Evelyn M. ; Sofaer, Helen R. ; Early, Regan ; Pearse, Ian S. ; Blumenthal, Dana M. ; Corbin, Jeffrey D. ; Diez, Jeffrey ; Dukes, Jeffrey S. ; Barnett, David T. ; Ibáñez, Inés ; et al ( August 2023 , Global Ecology and Biogeography)

   Native biodiversity is threatened by the spread of non‐native invasive species. Many studies demonstrate that invasions reduce local biodiversity but we lack an understanding of how impacts vary across environments at the macroscale. Using ~11,500 vegetation surveys from ecosystems across the United States, we quantified how the relationship between non‐native plant cover and native plant diversity varied across different compositions of invading plants (measured by non‐native plant richness and evenness) and environmental contexts (measured by productivity and human activity).

   Continental United States.

   Surveys from 1990s‐present.

   Terrestrial plant communities.

   We fit mixed effects models to understand how native plant richness, diversity and evenness varied with non‐native cover. We tested how this relationship varied when non‐native cover interacted with non‐native plant richness and evenness, and with productivity and human activity.

   Across the United States, communities with greater cover of non‐native plants had lower native plant richness and diversity but higher evenness, suggesting rare native plants can be lost while dominant plants decline in abundance. The relationship between non‐native cover and native community diversity varied with non‐native plant richness and evenness but was not associated with productivity and human activity. Negative associations were strongest in areas with low non‐native richness and evenness, characterizing plant communities that were invaded by a dominant non‐native plant.

   Non‐native plant cover provides a first approximation of invasion impacts on native community diversity, but the magnitude of impact depended on non‐native plant richness and evenness. Relationships between non‐native cover and native diversity were consistent in strength across continental scale gradients of productivity and human activity. Therefore, at the macroscale, invasive plant impacts on native plant communities likely depend more on the characteristics of the invading plants, that is the presence of a dominant invader, than on the environmental context.

    

   more » « less
2. SPCIS: Standardized Plant Community with Introduced Status database

   https://doi.org/10.1002/ecy.3947  

   Petri, Laís ; Beaury, Evelyn M. ; Corbin, Jeffrey ; Peach, Kristen ; Sofaer, Helen ; Pearse, Ian S. ; Early, Regan ; Barnett, David T. ; Ibáñez, Inés ; Peet, Robert K. ; et al ( January 2023 , Ecology)

   The movement of plant species across the globe exposes native communities to new species introductions. While introductions are pervasive, two aspects of variability underlie patterns and processes of biological invasions at macroecological scales. First, only a portion of introduced species become invaders capable of substantially impacting ecosystems. Second, species that do become invasive at one location may not be invasive in others; impacts depend on invader abundance and recipient species and conditions. Accounting for these phenomena is essential to accurately understand the patterns of plant invasion and explain the idiosyncratic results reflected in the literature on biological invasions. The lack of community‐level richness and the abundance of data spanning broad scales and environmental conditions have until now hindered our understanding of invasions at a macroecological scale. To address this limitation, we leveraged quantitative surveys of plant communities in the USA and integrated and harmonized nine datasets into the Standardized Plant Community with Introduced Status (SPCIS) database. The database contains 14,056 unique taxa identified within 83,391 sampling units, of which 52.6% have at least one introduced species. The SPCIS database includes comparable information on plant species occurrence, abundance, and native status across the 50 U.S. States and Puerto Rico. SPCIS can be used to answer macro‐scale questions about native plant communities and interactions with invasive plants. There are no copyright restrictions on the data, and we ask the users of this dataset to cite this paper, the respective paper(s) corresponding to the dataset sampling design (all references are provided in Data S1: Metadata S1: Class II‐B‐2), and the references described in Data S1: Metadata S1: Class III‐B‐4 as applicable to the dataset being utilized.

    

   more » « less
3. Expanding the invasion footprint: Ventenata dubia and relationships to wildfire, environment, and plant communities in the Blue Mountains of the Inland Northwest, USA

   https://doi.org/10.1111/avsc.12511  

   Tortorelli, Claire M. ; Krawchuk, Meg A. ; Kerns, Becky K. ; Fraser, ed., Lauchlan ( August 2020 , Applied Vegetation Science)

   A recently introduced non‐native annual grass,Ventenata dubia, is challenging previous conceptions of community resistance in forest mosaic communities in the Inland Northwest. However, little is known of the drivers and potential ecological impacts of this rapidly expanding species. Here we (1) identify abiotic and biotic habitat characteristics associated with theV. dubiainvasion and examine how these differ betweenV. dubiaand other problematic non‐native annual grasses,Bromus tectorumandTaeniatherum caput‐medusae; and (2) determine how burning influences relationships betweenV. dubiaand plant community composition and structure to address potential impacts on Inland Northwest forest mosaic communities.

   Blue Mountains of the Inland Northwest, USA.

   We measured environmental and plant community characteristics in 110 recently burned and nearby unburned plots. Plots were stratified to capture a range ofV. dubiacover, elevations, biophysical classes, and fire severities. We investigated relationships betweenV. dubia, wildfire, environmental, and plant community characteristics using non‐metric multidimensional scaling and linear regressions.

   Ventenata dubiawas most abundant in sparsely vegetated, basalt‐derived rocky scablands interspersed throughout the forested landscape. Plant communities most heavily invaded byV. dubiawere largely uninvaded by other non‐native annual grasses.Ventenata dubiawas abundant in both unburned and burned areas, but negative relationships betweenV. dubiacover and community diversity were stronger in burned plots, where keystone sagebrush species were largely absent after fire.

   Ventenata dubiais expanding the overall invasion footprint into previously uninvaded communities. Burning may exacerbate negative relationships betweenV. dubiaand species richness, evenness, and functional diversity, including in communities that historically rarely burned. Understanding the drivers and impacts of theV. dubiainvasion and recognizing how these differ from other annual grass invasions may provide insight into mechanisms of community invasibility, grass‐fire feedbacks, and aid the development of species‐specific management plans.

    

   more » « less
4. Wild herbivores enhance resistance to invasion by exotic cacti in an African savanna

   https://doi.org/10.1111/1365-2745.14010  

   Wells, Harry B. M. ; Crego, Ramiro D. ; Alston, Jesse M. ; Ndung'u, S. Kimani ; Khasoha, Leo M. ; Reed, Courtney G. ; Hassan, Abdikadir A. ; Kurukura, Samson ; Ekadeli, Jackson ; Namoni, Mathew ; et al ( October 2022 , Journal of Ecology)

   Whether wild herbivores confer biotic resistance to invasion by exotic plants remains a key question in ecology. There is evidence that wild herbivores can impede invasion by exotic plants, but it is unclear whether and how this generalises across ecosystems with varying wild herbivore diversity and functional groups of plants, particularly over long‐term (decadal) time frames.

   Using data from three long‐term (13‐ to 26‐year) exclosure experiments in central Kenya, we tested the effects of wild herbivores on the density of exotic invasive cacti,Opuntia strictaandO. ficus‐indica(collectively,Opuntia), which are among the worst invasive species globally. We also examined relationships between wild herbivore richness and elephant occurrence probability with the probability ofO. strictapresence at the landscape level (6150 km²).

   Opuntiadensities were 74% to 99% lower in almost all plots accessible to wild herbivores compared to exclosure plots.Opuntiadensities also increased more rapidly across time in plots excluding wild herbivores. These effects were largely driven by megaherbivores (≥1000 kg), particularly elephants.

   At the landscape level, modelledOpuntia strictaoccurrence probability was negatively correlated with estimated species richness of wild herbivores and elephant occurrence probability. On average,O. strictaoccurrence probability fell from ~0.56 to ~0.45 as wild herbivore richness increased from 6 to 10 species and fell from ~0.57 to ~0.40 as elephant occurrence probability increased from ~0.41 to ~0.84. These multi‐scale results suggest that any facilitative effects ofOpuntiaby wild herbivores (e.g. seed/vegetative dispersal) are overridden by suppression (e.g. consumption, uprooting, trampling).

   Synthesis. Our experimental and observational findings that wild herbivores confer resistance to invasion by exotic cacti add to evidence that conserving and restoring native herbivore assemblages (particularly megaherbivores) can increase community resistance to plant invasions.

    

   more » « less
5. Disturbance or propagule pressure? Unravelling the drivers and mapping the intensity of invasion of free‐ranging dogs across the Atlantic forest hotspot

   https://doi.org/10.1111/ddi.12845  

   Ribeiro, Fernando S. ; Nichols, Elizabeth ; Morato, Ronaldo G. ; Metzger, Jean Paul ; Pardini, Renata ; Santini, ed., Luca ( December 2018 , Diversity and Distributions)

   Identifying the drivers of biological invasions is crucial to predict the risk of invasion across broad spatial scales and to devise strategies to prevent invasion impacts. Here, we explore the relative importance and synergies between two key drivers—propagule pressure and landscape disturbance—in determining the invasion of native forest remnants by dogs, one of the most abundant, widely distributed, and harmful invasive species worldwide.

   Brazilian Atlantic Forest.

   Combining a camera trap dataset (96 sites in forest remnants) and censuses of populations of dogs raised by humans across 12 landscapes (2,830 ha each), we usedN‐mixture models that account for imperfect detection to confront alternative hypotheses of invasion drivers. We then used this empirical evidence to predict the intensity of dog invasion across the Atlantic Forest hotspot.

   Propagule pressure (density of raised dogs, positive effect) and landscape disturbance (forest cover, negative effect) were equally important drivers of dog invasion, presenting additive rather than synergistic effects. Dogs invade forest remnants far from their homes, making the density of raised dogs the key component of propagule pressure (relative to dog spatial distribution). Forest cover was more important than either the length or density of forest edges, suggesting that both reduced area of forested barriers to long‐distance movements and increased proximity of forests to edges facilitate dog access to forests. Across the Atlantic Forest, the combination of high human population density and extensive deforestation makes dog invasion an additional and widespread threat.

   Combined with available maps of priority areas for biodiversity conservation, our spatial prediction of dog invasion can help target areas for integrated management actions. These actions should go beyond measures to control dog populations and encompass the maintenance and restoration of native forests and strategic planning of afforestation through planted forests.

    

   more » « less