Predicting invasion in grassland ecosystems : is exotic dominance the real embarrassment of richness ?

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 grassdominated 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 siteor 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. Disciplines Agriculture | Biodiversity | Ecology and Evolutionary Biology | Terrestrial and Aquatic Ecology Comments This article is from Global Change Biology 19 (2013): 3677, doi:10.1111/gcb.12370 Rights 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. Authors Eric W. Seabloom, Elizabeth T. Borer, Yvonne M. Buckley, Elsa E. Cleland, Kendi F. Davies, Jennifer Firn, W. Stanley Harpole, Yann Hautier, Eric Lind, Andrew S. MacDougall, John L. Orrock, Suzanne M. Prober, Peter B. Adler, Juan Alberti, T. Michael Anderson, Jonathan D. Bakker, Lori A. Biederman, Dana Blumenthal, Cynthia S. Brown, Lars A. Brudvig, Maria Caldeira, Chengjin Chu, Michael J. Crawley, Pedro Daleo, Ellen I. Damschen, Carla M. D'Antonio, Nicole M. DeCrappeo, Chris R. Dickman, Guozhen Du, Philip A. Fay, Paul N. Frater, Daniel S. Gruner, Nicole Hagenah, Andrew Hector, Aveliina Helm, Helmut Hillebrand, Kirsten S. Hofmockel, Hope Humphries, Oscar Iribarne, Virginia L. Jin, Adam Kay, Kevin P. Kirkman, Julia A. Klein, This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/eeob_ag_pubs/7 Johannes M. H. Knops, Kimberly J. La Pierre, Laura M. Ladwig, John G. Lambrinos, Andrew D. B. Leakey, Qi Li, Wei Li, Rebecca L. McCulley, Brett A. Melbourne, Charles E. Mitchell, Joslin L. Moore, John Morgan, Brent D. Mortensen, Lydia R. O'Halloran, Meelis Partel, Jesus Pascual, David A. Pyke, Anita C. Risch, Roberto Salguero-Gomez, Mahesh Sankaran, Martin Schuetz, Anna Simonsen, Melinda Smith, Carly J. Stevens, Lauren Sullivan, Glenda M. Wardle, Elizabeth M. Wolkovich, Peter D. Wragg, Justin Wright, and Louie Yang This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/eeob_ag_pubs/7 Predicting invasion in grassland ecosystems: is exotic dominance the real embarrassment of richness? ER IC W . SEABLOOM , EL I ZABETH T . BORER 1 , YVONNE BUCKLEY 2 , EL SA E . CLELAND , KEND I DAV IE S 4 , J ENN I FER F IRN 5 , W . S TANLEY HARPOLE 6 , YANN HAUT IER 1 , 7 , E R IC L IND 1 , ANDREW MACDOUGALL 8 , JOHN L . ORROCK 9 , SUZANNE M . PROBER 1 0 , P ETER ADLER 1 1 , JUAN ALBERT I 1 2 , T . M ICHAEL ANDERSON 3 , JONATHAN D . BAKKER 1 4 , LOR I A . B I EDERMAN , DANA BLUMENTHAL 1 5 , CYNTH IA S . BROWN 6 , LARS A . BRUDV IG 1 7 , MAR IA CALDE IRA 1 8 , CHENG J IN CHU 9 , M ICHAEL J . CRAWLEY 2 0 , P EDRO DALEO 1 2 , E LLEN I . DAMSCHEN , CARLA M . D ’ANTON IO 2 1 , N ICOLE M . DECRAPPEO 2 2 , CHR I S R . D ICKMAN 3 , GUOZHEN DU 9 , PH I L I P A . FAY 2 4 , PAUL FRATER 6 , DAN IEL S . GRUNER 2 5 , N ICOLE HAGENAH 6 , 2 7 , ANDREW HECTOR 7 , AVEL I INA HELM 8 , HELMUT H ILLEBRAND 9 , K I R STEN S . HOFMOCKEL 6 , HOPE C . HUMPHR IE S 3 0 , O SCAR IR I BARNE 1 2 , V I RG IN IA L . J IN 3 1 , ADAM KAY 3 2 , KEV IN P . K IRKMAN 6 , JUL IA A . KLE IN 3 3 , JOHANNES M . H . KNOPS 3 4 , K IMBERLY J . LA P I ERRE 2 7 , LAURA M . LADWIG 3 5 , JOHN G . LAMBR INOS 3 6 , ANDREW D . B . L EAKEY 3 7 , Q I L I 3 8 , WE I L I 3 9 , REBECCA MCCULLEY 4 0 , BRETT MELBOURNE 4 , CHARLES E . M ITCHELL 4 1 , JO SL IN L . MOORE 4 2 , JOHN MORGAN 3 , BRENT MORTENSEN 6 , LYD IA R . O ’HALLORAN 4 , MEEL I S P € ARTEL 2 8 , J E S US PASCUAL 1 2 , DAV ID A . PYKE 2 2 , AN ITA C . R I SCH 4 5 , ROBERTO SALGUERO -G OMEZ 2 , MAHESH SANKARAN 6 , MART IN SCHUETZ 4 5 , ANNA S IMONSEN 4 7 , MEL INDA SMITH 4 8 , CARLY STEVENS 4 9 , LAUREN SULL IVAN , GLENDA M . WARDLE 2 3 , EL I ZABETH M .WOLKOV ICH 5 0 , P ETER D . WRAGG 1 , JU ST IN WR IGHT 5 1 and LOUIE YANG Department of Ecology, Evolution, and Behavior, University of MN, St. Paul, MN 55108, USA, ARC Centre of Excellence for Environmental Decisions, School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia, Ecology, Behavior & Evolution Section, University of California, San Diego, La Jolla, CA 92093, USA, Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA, Queensland University of Technology, Biogeosciences, Brisbane, Queensland 4000, Australia, Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA, Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH‐8057, Zurich, Switzerland, Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada, Department of Zoology, University of Wisconsin, Madison, WI 53706, USA, CSIRO Ecosystem Sciences, Private Bag 5, Wembley, WA 6913, Australia, Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT 84322, USA, Instituto de Investigaciones Marinas y Costeras (UNMdP-CONICET), Mar del Plata, Argentina, Department of Biology, Wake Forest University, Winston-Salem, NC 27109, USA, School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195-4115, USA, Rangeland Resources Research Unit, USDA Agricultural Research Service, Fort Collins, CO 80526, USA, Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523, USA, Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA, Centro de Estudos Florestais, Instituto Superior de Agronomia, Technical University of Lisbon, Lisbon, Portugal, School of Life Sciences, Lanzhou University, Lanzhou 730000, China, Department of Biology, Imperial College London, Silwood Park, Ascot SL5 7PY, UK, Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA, U.S. Geological Survey Forest and Rangeland Ecosystem Science Center, Corvallis, OR 97331, USA, Desert Ecology Research Group, School of Biological Sciences, University of Sydney, Sydney, NSW 2006, Australia, USDA-ARS Grassland Soil and Water Research Lab, Temple, TX 76502, USA, Department of Entomology, University of Maryland, College Park, MD 20742, USA, School of Life Sciences, University of KwaZulu-Natal, Scottsville, Pietermaritzburg 3209, South Africa, Department of Ecology, Evolutionary Biology, Yale University, New Haven, CT 06520, USA, Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia, Institute for Chemistry and Biology of the Marine Environment, Carl-von-Ossietzky University, Wilhelmshaven, Germany, INSTAAR, University of Colorado, Boulder, CO 80309-0450, USA, USDA-ARS Agroecosystem Management Research Unit, Lincoln, NE 68583, USA, Biology Department, University of St. Thomas, Saint Paul, MN 55105, USA, Department Forest, Rangeland & Watershed Stewardship, Colorado State University, Fort Collins, CO 80523-1472, USA, School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA, Department of Biology, University of New Mexico, Albuquerque, NM 87103, USA, Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA, Department of Plant Biology and Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA, Key Laboratory of Adaptation and Evolution of © 2013 John Wiley & Sons Ltd 3677 Global Change Biology (2013) 19, 3677–3687, doi: 10.1111/gcb.12370