Socioeconomic legacy yields an invasion debt
- aEnvironment Agency Austria, 1090 Vienna, Austria;
- bBio-Protection Research Centre, P.O. Box 84, Lincoln University, Lincoln 7647, Christchurch, New Zealand;
- cVienna Institute for Nature Conservation and Analyses, 1090 Vienna, Austria;
- dDepartment of Conservation Biology, Vegetation and Landscape Ecology, University of Vienna, 1030 Vienna, Austria;
- eInstitute of Botany, Academy of Sciences of the Czech Republic, 252 43 Průhonice, Czech Republic;
- fDepartment of Ecology, Faculty of Science, Charles University, 128 01 Praha 2, Czech Republic;
- gInstitute of Social Ecology, Alpen Adria Universität, 1070 Vienna, Austria;
- hUFZ, Helmholtz Centre for Environmental Research - UFZ, Department of Community Ecology, 06120 Halle, Germany;
- iInstitute of Ecology and Evolution, University of Bern, 3012 Bern, Switzerland;
- jEstación Biológica de Doñana (EBD-CSIC), E-41092 Seville, Spain;
- kInternational Union for Conservation of Nature Species Survival Commission, Invasive Species Specialist Group, Institute for Environmental Protection and Research, I-00185 Rome, Italy;
- lDipartimento di Biologia Evoluzionistica “Leo Pardi”, Università degli Studi di Firenze, 50125 Firenze, Italy;
- mInstitut National de la Recherche Agronomique , Unité Mixte de Recherche 1202 Biodiversité, Génes et Communautés, Pathologie Forestière, 33140 Villenave d'Ornon, France; and
- nInstitut National de la Recherche Agronomique UR633, Zoologie Forestière, 45075 Orléans, France
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Edited by Harold A. Mooney, Stanford University, Stanford, CA, and approved November 23, 2010 (received for review August 6, 2010)
↵1F.E. and S.D. contributed equally to this work.

Abstract
Globalization and economic growth are widely recognized as important drivers of biological invasions. Consequently, there is an increasing need for governments to address the role of international trade in their strategies to prevent species introductions. However, many of the most problematic alien species are not recent arrivals but were introduced several decades ago. Hence, current patterns of alien-species richness may better reflect historical rather than contemporary human activities, a phenomenon which might be called “invasion debt.” Here, we show that across 10 taxonomic groups (vascular plants, bryophytes, fungi, birds, mammals, reptiles, amphibians, fish, terrestrial insects, and aquatic invertebrates) in 28 European countries, current numbers of alien species established in the wild are indeed more closely related to indicators of socioeconomic activity from the year 1900 than to those from 2000, although the majority of species introductions occurred during the second half of the 20th century. The strength of the historical signal varies among taxonomic groups, with those possessing good capabilities for dispersal (birds, insects) more strongly associated with recent socioeconomic drivers. Nevertheless, our results suggest a considerable historical legacy for the majority of the taxa analyzed. The consequences of the current high levels of socioeconomic activity on the extent of biological invasions will thus probably not be completely realized until several decades into the future.
Footnotes
- 2To whom correspondence should be addressed. E-mail: stefan.dullinger{at}univie.ac.at.
Author contributions: F.E. and S.D. designed research; F.E., S.D., I. Kleinbauer, F.K., P.G., F.G., M.-L.D.-L., A.R., and P.P. performed research; S.D., P.E.H., K.H., V.J., and I. Kühn analyzed data; and F.E., S.D., W.R., P.E.H., V.J., I. Kühn, W.N., M.V., and P.P. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1011728108/-/DCSupplemental.
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