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United States Department of Agriculture

Agricultural Research Service


Location: Grassland, Soil and Water Research Laboratory

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

item Seabloom, Eric
item Borer, Elizabeth
item Buckley, Yvonne
item Cleland, Elsa
item Davies, Kendi
item Firn, Jennifer
item Harpole, Stanley
item Hautier, Yann
item Lind, Eric
item Macdougall, Andrew
item Orrock, John
item Prober, Suzanne
item Adler, Peter
item Alberti, Juan
item Anderson, T.
item Bakker, Jonathan
item Biederman, Lori
item Blumenthal, Dana
item Brown, Cynthia
item Brudvig, Lars
item Caldeira, Maria
item Chu, Chengjin
item Crawley, Michael
item Daleo, Pedro
item Damschen, Ellen
item D'antonio, Carla
item Decrappeo, Nicole
item Dickman, Chris
item Du, Guozhen
item Fay, Philip
item Frater, Paul
item Gruner, Daniel
item Hagenah, Nicole
item Hector, Andrew
item Helm, Aveliina
item Hillebrand, Helmut
item Hofmockel, Kirsten
item Humphries, Hope
item Iribarne, Oscar
item Jin, Virginia
item Kay, Adam
item Kirkman, Kevin
item Klein, Julia
item Knops, Johannes
item La Pierre, Kimberly
item Ladwig, Laura
item Lambrinos, John
item Leakey, Andrew
item Li, Qi
item Li, Wei
item Mcculley, Rebecca
item Melbourne, Brett
item Mitchell, Charles
item Moore, Joslin
item Morgan, John
item Mortensen, Brent
item O'halloran, Lydia
item Partel, Meelis
item Pascual, Jesus
item Pyke, David
item Risch, Anita
item Salguero-gomez, Roberto
item Sankaran, Mahesh
item Schuetz, Martin
item Simonsen, Anna
item Smith, Melinda
item Stevens, Carly
item Sullivan, Lauren
item Wardle, Glenda
item Wolkovich, Elizabeth
item Wragg, Peter
item Wright, Justin
item Yang, Louie

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2013
Publication Date: 10/16/2013
Publication URL:
Citation: Seabloom, E., Borer, E.T., Buckley, Y., Cleland, E., Davies, K., Firn, J., Harpole, S., Hautier, Y., Lind, E., Macdougall, A., Orrock, J.L., Prober, S.M., Adler, P., Alberti, J., Anderson, T.M., Bakker, J.D., Biederman, L.A., Blumenthal, D.M., Brown, C.S., Brudvig, L.A., Caldeira, M., Chu, C., Crawley, M.J., Daleo, P., Damschen, E.I., D'Antonio, C.M., Decrappeo, N.M., Dickman, C.R., Du, G., Fay, P.A., Frater, P., Gruner, D.S., Hagenah, N., Hector, A., Helm, A., Hillebrand, H., Hofmockel, K.S., Humphries, H.C., Iribarne, O., Jin, V.L., Kay, A., Kirkman, K.P., Klein, J.A., Knops, J.M., La Pierre, K.J., Ladwig, L.M., Lambrinos, J.G., Leakey, A.D., Li, Q., Li, W., McCulley, R., Melbourne, B., Mitchell, C.E., Moore, J.L., Morgan, J., Mortensen, B., O'Halloran, L.R., Partel, M., Pascual, J., Pyke, D.A., Risch, A.C., Salguero-Gomez, R., Sankaran, M., Schuetz, M., Simonsen, A., Smith, M., Stevens, C., Sullivan, L., Wardle, G.M., Wolkovich, E.M., Wragg, P.D., Wright, J., Yang, L. 2013. Predicting invasion in grassland ecosystems: Is exotic dominance the real embarrassment of richness? Global Change Biology. 19:3677-3687.

Interpretive Summary: Introduced exotic plant species comprise 20-80% of some plant communities, and can cause large losses in the abilities of ecosystems to provide crucial goods and services. However, not all systems become dominated by exotic species, and the reasons for their uneven distributions remain unclear. This study measured exotic plant species numbers (richness) and abundance (cover) in 54 grasslands from nine countries on four continents. We compared exotic species abundance with several factors that could influence abundance, including climate, and native species productivity and diversity. The study shows that exotic abundance is most strongly associated with geographic regions, and that species abundance was a better predictor than richness of exotic species impacts on ecosystems. Future studies of exotic species impacts should focus on their degree of dominance of the plant communities rather than on numbers of species.

Technical Abstract: For two centuries there has been a perception that while exotic species are dominant in many areas, others remain largely unaffected. This unquantified observation suggests a fundamental ecological question: why do exotics dominate some locations and not others? While invasions are clearly important globally, there have been no globally-replicated studies that measure exotic dominance. Rather, there has been a focus on exotic richness, because of the lack of standardized data on exotic abundance. We measured the richness and cover of exotic plant species in 54 grass-dominated ecosystems in nine countries on four continents, ranging from salt marshes to alpine tundra. We found that exotic richness was a poor proxy for exotic dominance at low levels of exotic richness, because exotic richness cannot resolve sites that had a few unimportant invaders (low exotic richness and cover) and those that were dominated by a few highly abundant exotics (low exotic richness and high exotic cover). We also quantified a bimodal pattern of invasion, with nearly all sites either dominated by exotic species or largely uninvaded, and few had an even mix of natives and exotics. Exotic dominance varied mostly among regions (subcontinents) and ecosystems with little variation among sites and blocks nested with ecosystem types. Exotic species were most dominant in areas that had low native grass richness at the site or regional scale suggesting a role for biotic resistance, as grasses comprise the most aggressive invaders. This work underscores the need to move beyond richness as a measure of exotic impact.

Last Modified: 10/19/2017
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