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重庆快乐十分计划网:Disentangling the abundance–impact relationship for invasive species
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The shape (linear vs. nonlinear), direction (negative vs. positive), and strength of the relationship between invasive alien species (IAS) abundance and native species diversity determines which invaders present the greatest risk to ecosystems. Yet, the form of the relationship between abundance and impact was previously unknown. Our metaanalyses reveal a strongly negative, convex relationship between invader abundance and native populations or communities when invaders are at higher trophic levels. Thus, on average, invasive species’ impacts are strongest at low invader abundance, highlighting the need for proactive policies to prevent introduction and eradicate early infestations. When invaders are at the same trophic levels, their impacts tended to be negative and linear, suggesting that treatment could benefit native communities regardless of invasion stage.
To predict the threat of biological invasions to native species, it is critical that we understand how increasing abundance of invasive alien species (IAS) affects native populations and communities. The form of this relationship across taxa and ecosystems is unknown, but is expected to depend strongly on the trophic position of the IAS relative to the native species. Using a global metaanalysis based on 1,258 empirical studies presented in 201 scientific publications, we assessed the shape, direction, and strength of native responses to increasing invader abundance. We also tested how native responses varied with relative trophic position and for responses at the population vs. community levels. As IAS abundance increased, native populations declined nonlinearly by 20%, on average, and community metrics declined linearly by 25%. When at higher trophic levels, invaders tended to cause a strong, nonlinear decline in native populations and communities, with the greatest impacts occurring at low invader abundance. In contrast, invaders at the same trophic level tended to cause a linear decline in native populations and communities, while invaders at lower trophic levels had no consistent impacts. At the community level, increasing invader abundance had significantly larger effects on species evenness and diversity than on species richness. Our results show that native responses to invasion depend critically on invasive species’ abundance and trophic position. Further, these general abundance–impact relationships reveal how IAS impacts are likely to develop during the invasion process and when to best manage them.
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Author contributions: B.A.B., R.W., A.E.B., J.M.D., and C.J.B.S. designed research; B.A.B., B.B.L., R.W., J.M.A., A.E.B., G.B., J.M.D., R.E., J.L., M.V., and C.J.B.S. performed research; R.W. contributed new reagents/analytic tools; B.A.B., R.W., and J.M.A. analyzed data; and B.A.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: Data used in the study are available on UMass Scholarworks at https://scholarworks.umass.edu/data/67/. R scripts used in the study are available on Zenodo at https://doi.org/10.5281/zenodo.2605254.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1818081116/-/DCSupplemental.
Published under the PNAS license.