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Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?
Global Change Biology
  • Eric W. Seabloom, University of Minnesota
  • Elizabeth T. Borer, University of Minnesota
  • Yvonne M. Buckley, University of Queensland
  • Elsa E. Cleland, University of California, San Diego
  • Kendi F. Davies, University of Colorado at Boulder
  • Jennifer Firn, Queensland University of Technology
  • W. Stanley Harpole, Iowa State University
  • Yann Hautier, University of Zurich
  • Eric Lind, University of Minnesota
  • Andrew S. MacDougall, University of Guelph
  • John L. Orrock, University of Wisconsin–Madison
  • Suzanne M. Prober, CSIRO Ecosystem Sciences
  • Peter B. Adler, Utah State University
  • Juan Alberti, Instituto de Investigaciones Marinas y Costeras
  • T. Michael Anderson, Wake Forest University
  • Jonathan D. Bakker, University of Washington
  • Lori A. Biederman, Iowa State University
  • Dana Blumenthal, USDA Agricultural Research Service
  • Cynthia S. Brown, Colorado State University - Fort Collins
  • Lars A. Brudvig, Michigan State University
  • Maria Caldeira, Technical University of Lisbon
  • Chengjin Chu, Lanzhou University
  • Michael J. Crawley, Imperial College London
  • Pedro Daleo, Instituto de Investigaciones Marinas y Costeras
  • Ellen I. Damschen, University of Wisconsin–Madison
  • Carla M. D'Antonio, University of California, Santa Barbara
  • Nicole M. DeCrappeo, United States Geological Survey
  • Chris R. Dickman, University of Sydney
  • Guozhen Du, Lanzhou University
  • Philip A. Fay, USDA-ARS Grassland Soil and Water Research Lab
  • Paul N. Frater, Iowa State University
  • Daniel S. Gruner, University of Maryland
  • Nicole Hagenah, University of KwaZulu-Natal
  • Andrew Hector, University of Zurich
  • Aveliina Helm, University of Tartu
  • Helmut Hillebrand, Carl-von-Ossietzky University
  • Kirsten S. Hofmockel, Iowa State University
  • Hope Humphries, University of Colorado at Boulder
  • Oscar Iribarne, Instituto de Investigaciones Marinas y Costeras
  • Virginia L. Jin, USDA-ARS Agroecosystem Management Research Unit
  • Adam Kay, University of St. Thomas
  • Kevin P. Kirkman, University of KwaZulu-Natal
  • Julia A. Klein, Colorado State University - Fort Collins
  • Johannes M. H. Knops, University of Nebraska–Lincoln
  • Kimberly J. La Pierre, Yale University
  • Laura M. Ladwig, University of New Mexico - Main Campus
  • John G. Lambrinos, Oregon State University
  • Andrew D. B. Leakey, University of Illinois
  • Qi Li, Chinese Academy of Sciences
  • Wei Li, Southwest Forestry University
  • Rebecca L. McCulley, University of Kentucky
  • Brett A. Melbourne, University of Colorado at Boulder
  • Charles E. Mitchell, University of North Carolina at Chapel Hill
  • Joslin L. Moore, University of Melbourne
  • John Morgan, La Trobe University
  • Brent D. Mortensen, Iowa State University
  • Lydia R. O'Halloran, Oregon State University
  • Meelis Partel, University of Tartu
  • Jesus Pascual, Instituto de Investigaciones Marinas y Costeras
  • David A. Pyke, U.S. Geological Survey Forest and Rangeland Ecosystem Science Center
  • Anita C. Risch, Swiss Federal Institute for Forest, Snow and Landscape Research
  • Roberto Salguero-Gomez, The University of Queensland
  • Mahesh Sankaran, National Centre for Biological Sciences
  • Martin Schuetz, Swiss Federal Institute for Forest, Snow and Landscape Research
  • Anna Simonsen, University of Toronto
  • Melinda Smith, Colorado State University - Fort Collins
  • Carly J. Stevens, Lancaster University
  • Lauren Sullivan, Iowa State University
  • Glenda M. Wardle, University of Sydney
  • Elizabeth M. Wolkovich, University of British Columbia
  • Peter D. Wragg, University of Minnesota
  • Justin Wright, Duke University
  • Louie Yang, University of California - Davis
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Invasions have increased the size of regional species pools, but are typically assumed to reduce native diversity. However, global-scale tests of this assumption have been elusive because of the focus on exotic species richness, rather than relative abundance. This is problematic because low invader richness can indicate invasion resistance by the native community or, alternatively, dominance by a single exotic species. Here, we used a globally replicated study to quantify relationships between exotic richness and abundance in grass-dominated ecosystems in 13 countries on six continents, ranging from salt marshes to alpine tundra. We tested effects of human land use, native community diversity, herbivore pressure, and nutrient limitation on exotic plant dominance. Despite its widespread use, exotic richness was a poor proxy for exotic dominance at low exotic richness, because sites that contained few exotic species ranged from relatively pristine (low exotic richness and cover) to almost completely exotic-dominated ones (low exotic richness but high exotic cover). Both exotic cover and richness were predicted by native plant diversity (native grass richness) and land use (distance to cultivation). Although climate was important for predicting both exotic cover and richness, climatic factors predicting cover (precipitation variability) differed from those predicting richness (maximum temperature and mean temperature in the wettest quarter). Herbivory and nutrient limitation did not predict exotic richness or cover. Exotic dominance was greatest in areas with low native grass richness at the site- or regional-scale. Although this could reflect native grass displacement, a lack of biotic resistance is a more likely explanation, given that grasses comprise the most aggressive invaders. These findings underscore the need to move beyond richness as a surrogate for the extent of invasion, because this metric confounds monodominance with invasion resistance. Monitoring species' relative abundance will more rapidly advance our understanding of invasions.

This article is from Global Change Biology 19 (2013): 3677, doi:10.1111/gcb.12370

Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted.
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Eric W. Seabloom, Elizabeth T. Borer, Yvonne M. Buckley, Elsa E. Cleland, et al.. "Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness?" Global Change Biology Vol. 19 (2013) p. 3677 - 3687
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