BACKGROUND AND AIMS: Since its emergence in the mid-20th century, invasion biology has matured into a productive research field addressing questions of fundamental and applied importance. Not only has the number of empirical studies increased through time, but also has the number of competing, overlapping and, in some cases, contradictory hypotheses about biological invasions. To make these contradictions and redundancies explicit, and to gain insight into the field's current theoretical structure, we developed and applied a Delphi approach to create a consensus network of 39 existing invasion hypotheses. RESULTS: The resulting network was analysed with a link-clustering algorithm that revealed five concept clusters (resource availability, biotic interaction, propagule, trait and Darwin's clusters) representing complementary areas in the theory of invasion biology. The network also displays hypotheses that link two or more clusters, called connecting hypotheses, which are important in determining network structure. The network indicates hypotheses that are logically linked either positively (77 connections of support) or negatively (that is, they contradict each other; 6 connections). SIGNIFICANCE: The network visually synthesizes how invasion biology's predominant hypotheses are conceptually related to each other, and thus, reveals an emergent structure - a conceptual map - that can serve as a navigation tool for scholars, practitioners and students, both inside and outside of the field of invasion biology, and guide the development of a more coherent foundation of theory. Additionally, the outlined approach can be more widely applied to create a conceptual map for the larger fields of ecology and biogeography.

Berlin Brandenburg Institute of Advanced Biodiversity Research Berlin Germany

Bio Protection Research Centre Lincoln University Lincoln Canterbury New Zealand

Biodiversity Research Systematic Botany University of Potsdam Potsdam Germany

Biological Sciences University of Southampton Southampton United Kingdom

Cary Institute of Ecosystem Studies Millbrook New York United States

Centre for Invasion Biology Department of Botany and Zoology Stellenbosch University Matieland South Africa

Centre for Invasion Biology Department of Mathematical Sciences Stellenbosch University Matieland South Africa

Czech Academy of Sciences Institute of Botany Department of Invasion Ecology Průhonice Czech Republic

Department of Biology Chemistry Pharmacy Institute of Biology Freie Universität Berlin Berlin Germany

Department of Botany and Biodiversity Research University of Vienna Vienna Austria

Department of Ecology Faculty of Science Charles University Prague Czech Republic

Department of Geography King's College London London United Kingdom

Department of Plant Biology and Ecology University of Seville Seville Spain

Ecology Department of Biology University of Konstanz Konstanz Germany

Ecology Evolution and Natural Resources Rutgers University New Brunswick New Jersey

Estación Biológica de Doñana Seville Spain

German Centre for Integrative Biodiversity Research Halle Jena Leipzig Leipzig Germany

Graham Sustainability Institute University of Michigan Ann Arbor Michigan United States

Helmholtz Centre for Environmental Research UFZ Department Community Ecology Halle Germany

Institute of Integrative Biology Department of Environmental Systems Science ETH Zurich Zurich Switzerland

Instituto de Recursos Naturales y Agrobiología de Sevilla CSIC Seville Spain

Leibniz Institute of Freshwater Ecology and Inland Fisheries Berlin Germany

Martin Luther University Halle Wittenberg Institute of Biology Geobotany and Botanical Garden Halle Germany

Ocean and Earth Science National Oceanography Centre University of Southampton Southampton United Kingdom

Philosophische Fakultät Institut für Bibliotheks und Informationswissenschaft Humboldt Universität zu Berlin Berlin Germany

Redpath Museum McGill University Montreal Quebec Canada

School of Biological Sciences Monash University Clayton Victoria Australia

School of BioSciences The University of Melbourne Parkville Victoria Australia

South African National Biodiversity Institute Kirstenbosch National Botanical Gardens Claremont South Africa

Technical University of Munich Freising Germany

The University of Rhode Island Department of Natural Resources Science Kingston Rhode Island

Zhejiang Provincial Key Laboratory of Plant Evolutionary Ecology and Conservation Taizhou University Taizhou China

Zobrazit více v PubMed

Ahn, Y. Y. , Bagrow, J. P. , & Lehmann, S. (2010). Link communities reveal multiscale complexity in networks. Nature, 466, 761–764. 10.1038/nature09182 PubMed DOI

Baker, H. G. (1965). Characteristics and modes of origin of weeds. In Baker H. G., & Stebbins G. L. (Eds.), The genetics of colonizing species; proceedings (pp. 147–168). New York, NY: Academic Press.

Baker, H. G. (1974). The evolution of weeds. Annual Review of Ecology and Systematics, 5, 1–24. 10.1146/annurev.es.05.110174.000245 DOI

Blackburn, T. M. , Pyšek, P. , Bacher, S. , Carlton, J. T. , Duncan, R. P. , Jarošík, V. , … Richardson, D. M. (2011). A proposed unified framework for biological invasions. Trends in Ecology and Evolution, 26, 333–339. 10.1016/j.tree.2011.03.023 PubMed DOI

Blossey, B. , & Nötzold, R. (1995). Evolution of increased competitive ability in invasive nonindigenous plants—A hypothesis. Journal of Ecology, 83, 887–889. 10.2307/2261425 DOI

Blumenthal, D. M. (2006). Interactions between resource availability and enemy release in plant invasion. Ecology Letters, 9, 887–895. 10.1111/j.1461-0248.2006.00934.x PubMed DOI

Börner, K. (2010). Atlas of science: Visualizing what we know. Cambridge, MA: MIT Press. PubMed PMC

Börner, K. (2015). Atlas of knowledge: Anyone can map. Cambridge, MA: MIT Press.

Callaway, R. M. , & Ridenour, W. M. (2004). Novel weapons: Invasive success and the evolution of increased competitive ability. Frontiers in Ecology and the Environment, 2, 436–443. 10.2307/3868432 DOI

Callaway, R. M. , Thelen, G. C. , Rodriguez, A. , & Holben, W. E. (2004). Soil biota and exotic plant invasion. Nature, 427, 731–733. 10.1038/nature02322 PubMed DOI

Capellini, I. , Baker, J. , Allen, W. L. , Street, S. E. , & Venditti, C. (2015). The role of life history traits in mammalian invasion success. Ecology Letters, 18, 1099–1107. 10.1111/ele.12493 PubMed DOI PMC

Catford, J. A. , Jansson, R. , & Nilsson, C. (2009). Reducing redundancy in invasion ecology by integrating hypotheses into a single theoretical framework. Diversity and Distributions, 15, 22–40. 10.1111/j.1472-4642.2008.00521.x DOI

Chabrerie, O. , Massol, F. , Facon, B. , Thevenoux, R. , Hess, M. , Ulmer, R. , … Renault, D. (2019). Biological invasion theories: Merging perspectives from population, community and ecosystem scales. Preprints. 2019100327

Colautti, R. I. , Grigorovich, I. A. , & MacIsaac, H. J. (2006). Propagule pressure: A null model for biological invasions. Biological Invasions, 8, 1023–1037. 10.1007/s10530-005-3735-y DOI

Colautti, R. I. , Ricciardi, A. , Grigorovich, I. A. , & MacIsaac, H. J. (2004). Is invasion success explained by the enemy release hypothesis? Ecology Letters, 7, 721–733. 10.1111/j.1461-0248.2004.00616.x DOI

Crawley, M. J. , Brown, S. L. , Heard, M. S. , & Edwards, G. R. (1999). Invasion‐resistance in experimental grassland communities: Species richness or species identity? Ecology Letters, 2, 140–148. 10.1046/j.1461-0248.1999.00056.x DOI

Csardi, G. , & Nepusz, T. (2006). The igraph software package for complex network research. InterJournal, Complex Systems, 1695. http://igraph.org

Daehler, C. C. (2001). Darwin's naturalization hypothesis revisited. The American Naturalist, 158, 324–330. 10.1086/321316 PubMed DOI

Darwin, C. (1859). On the origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life. London, UK: J. Murray. PubMed PMC

Davis, M. A. , Grime, J. P. , & Thompson, K. (2000). Fluctuating resources in plant communities: A general theory of invasibility. Journal of Ecology, 88, 528–534. 10.1046/j.1365-2745.2000.00473.x DOI

Diamond, J. , & Case, T. J. (1986). Overview: Introductions, extinctions, exterminations, and invasions. In Diamond J. & Case T. J. (Eds.), Community ecology (pp. 65–79). New York, NY: Harper and Row.

Divíšek, J. , Chytry, M. , Beckage, B. , Gotelli, N. J. , Lososova, Z. , Pysek, P. , … Molofsky, J. (2018). Similarity of introduced plant species to native ones facilitates naturalization, but differences enhance invasion success. Nature Communications, 9, 4631. 10.1038/s41467-018-06995-4 PubMed DOI PMC

Doorduin, L. J. , & Vrieling, K. (2011). A review of the phytochemical support for the shifting defence hypothesis. Phytochemistry Reviews, 10, 99–106. 10.1007/s11101-010-9195-8 PubMed DOI PMC

Duncan, R. P. , & Williams, P. A. (2002). Ecology—Darwin's naturalization hypothesis challenged. Nature, 417, 608–609. 10.1038/417608a PubMed DOI

Elton, C. S. (1958). The ecology of invasions by animals and plants. London, UK: Methuen.

Enders, M. , Havemann, F. , & Jeschke, J. M. (2019). A citation‐based map of concepts in invasion biology. NeoBiota, 47, 23–42. 10.3897/neobiota.47.32608 DOI

Enders, M. , Hütt, M.‐T. , & Jeschke, J. M. (2018). Drawing a map of invasion biology based on a network of hypotheses. Ecosphere, 9, e02146. 10.1002/ecs2.2146 DOI

Enders, M. , & Jeschke, J. M. (2018). A network of invasion hypotheses. In Jeschke J. M. & Heger T. (Eds.), Invasion biology: Hypotheses and evidence (pp. 49–59). Wallingford, UK: CABI.

Eppinga, M. B. , Rietkerk, M. , Dekker, S. C. , De Ruiter, P. C. , Van der Putten, W. H. , & Van der Putten, W. H. (2006). Accumulation of local pathogens: A new hypothesis to explain exotic plant invasions. Oikos, 114, 168–176. 10.1111/j.2006.0030-1299.14625.x DOI

Evans, T. S. , & Lambiotte, R. (2009). Line graphs, link partitions, and overlapping communities. Physical Review E, 80, 016105. 10.1103/PhysRevE.80.016105 PubMed DOI

Fortunato, S. (2010). Community detection in graphs. Physics Reports, 486, 75–174. 10.1016/j.physrep.2009.11.002 DOI

Fridley, J. D. , & Sax, D. F. (2014). The imbalance of nature: Revisiting a Darwinian framework for invasion biology. Global Ecology and Biogeography, 23, 1157–1166. 10.1111/geb.12221 DOI

Gurevitch, J. , Fox, G. A. , Wardle, G. M. , Inderjit, & Taub, D. (2011). Emergent insights from the synthesis of conceptual frameworks for biological invasions. Ecology Letters, 14, 407–418. 10.1111/j.1461-0248.2011.01594.x PubMed DOI

Häder, M. , & Häder, S. (Eds.) (2000). Die Delphi‐Technik in den Sozialwissenschaften: Methodische Forschungen und innovative Anwendungen. Wiesbaden, Germany: VS Verlag für Sozialwissenschaften.

Handcock, M. S. , Hunter, D. R. , Butts, C. T. , Goodreau, S. M. , & Morris, M. (2003). statnet: Software tools for the statistical modeling of network data. http://statnetproject.org PubMed PMC

Havemann, F. , Gläser, J. , & Heinz, M. (2017). Memetic search for overlapping topics based on a local evaluation of link communities. Scientometrics, 111, 1089–1118. 10.1007/s11192-017-2302-5 DOI

Havemann, F. , Gläser, J. , & Heinz, M. (2019). Communities as well separated subgraphs with cohesive cores: Identification of core‐periphery structures in link communities. In Aiello L. M., Cherifi C., Cherifi H., Lambiotte R., Lio P., & Rocha L. M. (Eds.), Complex networks and their applications VII, Studies in computational intelligence (pp. 219–230). Basel, Switzerland: Springer Nature Switzerland. 10.1007/978-3-030-05411-3_18 DOI

Heger, T. , Bernard‐Verdier, M. , Gessler, A. , Greenwood, A. D. , Grossart, H.‐P. , Hilker, M. , … Jeschke, J. M. (2019). Towards an integrative, eco‐evolutionary understanding of ecological novelty: Studying and communicating interlinked effects of global change. BioScience, 69, 888–899. 10.1093/biosci/biz095 PubMed DOI PMC

Hobbs, R. J. , & Huenneke, L. F. (1992). Disturbance, diversity, and invasion—Implications for conservations. Conservation Biology, 6, 324–337. 10.1046/j.1523-1739.1992.06030324.x DOI

Huston, M. (1979). A general hypothesis of species diversity. The American Naturalist, 113, 81–101. 10.1086/283366 DOI

Jeschke, J. M. (2008). Across islands and continents, mammals are more successful invaders than birds. Diversity and Distributions, 14, 913–916. 10.1111/j.1472-4642.2008.00488.x DOI

Jeschke, J. M. (2014). General hypotheses in invasion ecology. Diversity and Distributions, 20, 1229–1234. 10.1111/ddi.12258 DOI

Jeschke, J. M. , Gómez Aparicio, L. , Haider, S. , Heger, T. , Lortie, C. J. , Pyšek, P. , & Strayer, D. L. (2012). Taxonomic bias and lack of cross‐taxonomic studies in invasion biology. Frontiers in Ecology and the Environment, 10, 349–350. 10.1890/12.WB.016 DOI

Jeschke, J. M. , & Heger, T. (2018). Invasion biology: Hypotheses and evidence. Wallingford, UK: CABI.

Jeschke, J. M. , & Strayer, D. L. (2006). Determinants of vertebrate invasion success in Europe and North America. Global Change Biology, 12, 1608–1619. 10.1111/j.1365-2486.2006.01213.x DOI

Johnstone, I. M. (1986). Plant invasion windows—A time‐based classification of invasion potential. Biological Reviews of the Cambridge Philosophical Society, 61, 369–394. 10.1111/j.1469-185X.1986.tb00659.x DOI

Keane, R. M. , & Crawley, M. J. (2002). Exotic plant invasions and the enemy release hypothesis. Trends in Ecology and Evolution, 17, 164–170. 10.1016/S0169-5347(02)02499-0 DOI

Kueffer, C. (2017). Plant invasions in the Anthropocene. Science, 358, 724–725. 10.1126/science.aao6371 PubMed DOI

Levine, J. M. , & D'Antonio, C. M. (1999). Elton revisited: A review of evidence linking diversity and invasibility. Oikos, 87, 15–26. 10.2307/3546992 DOI

Lively, C. M. (2010). The effect of host genetic diversity on disease spread. The American Naturalist, 175, E149–E152. 10.1086/652430 PubMed DOI

Lockwood, J. L. , Cassey, P. , & Blackburn, T. (2005). The role of propagule pressure in explaining species invasions. Trends in Ecology and Evolution, 20, 223–228. 10.1016/j.tree.2005.02.004 PubMed DOI

Lockwood, J. L. , Cassey, P. , & Blackburn, T. M. (2009). The more you introduce the more you get: The role of colonization pressure and propagule pressure in invasion ecology. Diversity and Distributions, 15, 904–910. 10.1111/j.1472-4642.2009.00594.x DOI

MacArthur, R. (1970). Species packing and competitive equilibrium for many species. Theoretical Population Biology, 1, 1–11. 10.1016/0040-5809(70)90039-0 PubMed DOI

MacArthur, R. , & Levins, R. (1967). Limiting similarity convergence and divergence of coexisting species. The American Naturalist, 101, 377–385. 10.1086/282505 DOI

Mahoney, P. J. , Beard, K. H. , Durso, A. M. , Tallian, A. G. , Long, A. L. , Kindermann, R. J. , … Mohn, H. E. (2015). Introduction effort, climate matching and species traits as predictors of global establishment success in non‐native reptiles. Diversity and Distributions, 21, 64–74. 10.1111/ddi.12240 DOI

Melbourne, B. A. , Cornell, H. V. , Davies, K. F. , Dugaw, C. J. , Elmendorf, S. , Freestone, A. L. , … Yokomizo, H. (2007). Invasion in a heterogeneous world: Resistance, coexistence or hostile takeover? Ecology Letters, 10, 77–94. 10.1111/j.1461-0248.2006.00987.x PubMed DOI

Mitchell, C. E. , Agrawal, A. A. , Bever, J. D. , Gilbert, G. S. , Hufbauer, R. A. , Klironomos, J. N. , … Vazquez, D. P. (2006). Biotic interactions and plant invasions. Ecology Letters, 9, 726–740. 10.1111/j.1461-0248.2006.00908.x PubMed DOI

Prinzing, A. , Durka, W. , Klotz, S. , & Brandl, R. (2001). The niche of higher plants: Evidence for phylogenetic conservatism. Proceedings of the Royal Society B: Biological Sciences, 268, 2383–2389. 10.1098/rspb.2001.1801 PubMed DOI PMC

Pulliam, H. R. (2000). On the relationship between niche and distribution. Ecology Letters, 3, 349–361. 10.1046/j.1461-0248.2000.00143.x DOI

Pyšek, P. , & Richardson, D. M. (2007). Traits associated with invasiveness in alien plants: Where do we stand? In Nentwig W. E. (Ed.), Biological invasions (pp. 97–125). Berlin, Germany: Springer‐Verlag.

R Development Core Team (2018). R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; http://www.R‐project.org

Rejmánek, M. , & Richardson, D. M. (1996). What attributes make some plant species more invasive? Ecology, 77, 1655–1661. 10.2307/2265768 DOI

Ricciardi, A. , & Atkinson, S. K. (2004). Distinctiveness magnifies the impact of biological invaders in aquatic ecosystems. Ecology Letters, 7, 781–784. 10.1111/j.1461-0248.2004.00642.x DOI

Richards, C. L. , Bossdorf, O. , Muth, N. Z. , Gurevitch, J. , & Pigliucci, M. (2006). Jack of all trades, master of some? On the role of phenotypic plasticity in plant invasions. Ecology Letters, 9, 981–993. 10.1111/j.1461-0248.2006.00950.x PubMed DOI

Richardson, D. M. , Allsopp, N. , D'Antonio, C. M. , Milton, S. J. , & Rejmanek, M. (2000). Plant invasions—The role of mutualisms. Biological Reviews, 75, 65–93. 10.1017/S0006323199005435 PubMed DOI

Richardson, D. M. , & Pyšek, P. (2008). Fifty years of invasion ecology—The legacy of Charles Elton. Diversity and Distributions, 14, 161–168. 10.1111/j.1472-4642.2008.00464.x DOI

Sala, O. E. , Chapin, F. S. , Armesto, J. J. , Berlow, E. , Bloomfield, J. , Dirzo, R. , … Wall, D. H. (2000). Biodiversity—Global biodiversity scenarios for the year 2100. Science, 287, 1770–1774. 10.1126/science.287.5459.1770 PubMed DOI

Schulz, A. N. , Lucardi, R. D. , & Marsico, T. D. (2019). Successful invasions and failed biocontrol: The role of antagonistic species Interactions. BioScience, 69, 711–724. 10.1093/biosci/biz075 DOI

Settele, J. , Hammen, V. , Hulme, P. , Karlson, U. , Klotz, S. , Kotarac, M. , … Kuhn, I. (2005). ALARM: Assessing LArge‐scale environmental Risks for biodiversity with tested Methods. Gaia, 14, 69–72. 10.14512/gaia.14.1.20 DOI

Shea, K. , & Chesson, P. (2002). Community ecology theory as a framework for biological invasions. Trends in Ecology and Evolution, 17, 170–176. 10.1016/S0169-5347(02)02495-3 DOI

Sher, A. A. , & Hyatt, L. A. (1999). The disturbed resource‐flux invasion matrix: A new framework for patterns of plant invasion. Biological Invasions, 1, 107–114. 10.1023/A:1010050420466 DOI

Simberloff, D. , & Gibbons, L. (2004). Now you see them, now you don't—Population crashes of established introduced species. Biological Invasions, 6, 161–172. 10.1023/B:Binv.0000022133.49752.46 DOI

Simberloff, D. , & Holle, B. V. (1999). Positive interactions of nonindigenous species: Invasional meltdown? Biological Invasions, 1, 21–32.

Sommer, S. (2005). The importance of immune gene variability (MHC) in evolutionary ecology and conservation. Frontiers in Zoology, 2, 16. 10.1186/1742-9994-2-16 PubMed DOI PMC

Stohlgren, T. J. , Jarnevitch, C. , & Chong, G. W. (2006). Scale and plant invasions: A theory of biotic acceptance. Preslia, 78, 405–426.

Swanson, D. R. (1986). Undiscovered public knowledge. Library Quarterly, 56, 103–118. 10.1086/601720 DOI

te Beest, M. , Le Roux, J. J. , Richardson, D. M. , Brysting, A. K. , Suda, J. , Kubešová, M. , & Pysek, P. (2012). The more the better? The role of polyploidy in facilitating plant invasions. Annals of Botany, 109, 19–45. 10.1093/aob/mcr277 PubMed DOI PMC

Thuiller, W. , Gallien, L. , Boulangeat, I. , de Bello, F. , Munkemuller, T. , Roquet, C. , & Lavergne, S. (2010). Resolving Darwin's naturalization conundrum: A quest for evidence. Diversity and Distributions, 16, 461–475. 10.1111/j.1472-4642.2010.00645.x DOI

Trujillo, C. M. , & Long, T. M. (2018). Document co‐citation analysis to enhance transdisciplinary research. Science Advances, 4, e1701130. 10.1126/sciadv.1701130 PubMed DOI PMC

van Kleunen, M. , Weber, E. , & Fischer, M. (2010). A meta‐analysis of trait differences between invasive and non‐invasive plant species. Ecology Letters, 13, 235–245. 10.1111/j.1461-0248.2009.01418.x PubMed DOI

Vaz, A. S. , Kueffer, C. , Kull, C. A. , Richardson, D. M. , Schindler, S. , Muñoz‐Pajares, A. J. , … Honrado, J. P. (2017). The progress of interdisciplinarity in invasion science. Ambio, 46, 428–442. 10.1007/s13280-017-0897-7 PubMed DOI PMC

Vidal‐Garcia, M. , & Keogh, J. S. (2017). Invasive cane toads are unique in shape but overlap in ecological niche compared to Australian native frogs. Ecology and Evolution, 7, 7609–7619. 10.1002/ece3.3253 PubMed DOI PMC

Wang, T. , Hu, J. T. , Wang, R. Q. , Liu, C. H. , & Yu, D. (2018). Tolerance and resistance facilitate the invasion success of Alternanthera philoxeroides in disturbed habitats: A reconsideration of the disturbance hypothesis in the light of phenotypic variation. Environmental and Experimental Botany, 153, 135–142. 10.1016/j.envexpbot.2018.05.011 DOI

Weiher, E. , & Keddy, P. A. (1995). Assembly rules, null models, and trait dispersion—New questions front old patterns. Oikos, 74, 159–164. 10.2307/3545686 DOI

Wickham, H. (2007). Reshaping data with the reshape package. Journal of Statistical Software, 21, 12. http://www.jstatsoft.org/v21/i12/

Williamson, M. H. , & Brown, K. C. (1986). The analysis and modelling of British invasions. Philosophical Transactions of the Royal Society of London Series B, Biological Sciences, 314, 505–522. 10.1098/rstb.1986.0070 DOI

Disentangling the relationships among abundance, invasiveness and invasibility in trait space

Plant-soil interactions in the native range of two congeneric species with contrasting invasive success

Dimensions of invasiveness: Links between local abundance, geographic range size, and habitat breadth in Europe's alien and native floras

The Hierarchy-of-Hypotheses Approach: A Synthesis Method for Enhancing Theory Development in Ecology and Evolution