Human-Mediated Dispersal and the Rewiring of Spatial Networks
Authors: James M. Bullock, Dries Bonte, Gesine Pufal, Carolina da Silva Carvalho, Daniel S. Chapman, Cristina García, Daniel García, Erik Matthysen, Maria Mar Delgado
Journal: Trends in Ecology & Evolution (2018)

Research into human impacts on biodiversity would benefit from considering HMD as a central process, in particular the wide variety of anthropogenic influences on the dispersal of organisms. Particular species or genotypes benefit from increased dispersal ability under HMD, including new linkages among areas of suitable habitat; conversely, others suffer from loss of dispersal opportunities and linkages, as well as increased costs. In total, HMD is expected to rewire spatial networks through the reconfiguration of links among nodes, particularly by changing the distances over which individuals disperse and the creation of highly connected nodes (hubs). As human impacts on the environment increase, ecology and conservation will benefit from considering rewiring holistically, assessing both the positive and negative impacts of HMD on eco-evolutionary dynamics. Humans fundamentally affect dispersal, directly by transporting individuals and indirectly by altering landscapes and natural vectors. This human-mediated dispersal (HMD) modifies long-distance dispersal, changes dispersal paths, and overall benefits certain species or genotypes while disadvantaging others. HMD is leading to radical changes in the structure and functioning of spatial networks, which are likely to intensify as human activities increase in scope and extent. Here, we provide an overview to guide research into HMD and the resulting rewiring of spatial networks, making predictions about the ecological and evolutionary consequences and how these vary according to spatial scale and the traits of species. Future research should consider HMD holistically, assessing the range of direct and indirect processes to understand the complex impacts on eco-evolutionary dynamics. Humans fundamentally affect dispersal, directly by transporting individuals and indirectly by altering landscapes and natural vectors. This human-mediated dispersal (HMD) modifies long-distance dispersal, changes dispersal paths, and overall benefits certain species or genotypes while disadvantaging others. HMD is leading to radical changes in the structure and functioning of spatial networks, which are likely to intensify as human activities increase in scope and extent. Here, we provide an overview to guide research into HMD and the resulting rewiring of spatial networks, making predictions about the ecological and evolutionary consequences and how these vary according to spatial scale and the traits of species. Future research should consider HMD holistically, assessing the range of direct and indirect processes to understand the complex impacts on eco-evolutionary dynamics. Dispersal has become increasingly recognised as an essential process in ecology and evolution, and the past 20 years have produced exciting new approaches to understanding dispersal (Box 1). An area of particular interest is the role of dispersal in the ecological and evolutionary responses of species to anthropogenic environmental change [1Thompson P.L. Gonzalez A. Dispersal governs the reorganization of ecological networks under environmental change.Nat. Ecol. Evol. 2017; 1: 0162Crossref PubMed Scopus (63) Google Scholar, 2Travis J.M.J. et al.Dispersal and species' responses to climate change.Oikos. 2013; 122: 1532-1540Crossref Scopus (267) Google Scholar]. For example, dispersal patterns are critical in determining the ability of species to track a changing climate or to survive habitat loss [3Santini L. et al.A trait-based approach for predicting species responses to environmental change from sparse data: how well might terrestrial mammals track climate change?.Global Change Biol. 2016; 22: 2415-2424Crossref PubMed Scopus (55) Google Scholar, 4Bullock J.M. et al.Modelling spread of British wind-dispersed plants under future wind speeds in a changing climate.J. Ecol. 2012; 100: 104-115Crossref Scopus (74) Google Scholar]. However, humans also affect the dispersal process itself in a variety of ways, the result of which can be characterised as human-mediated dispersal (HMD; see Glossary). Here, we distinguish two forms of HMD. Human-vectored dispersal (HVD) occurs when humans transport organisms directly. Human-altered dispersal (HAD) encompasses the indirect effects of humans on dispersal by altering landscape structure, dispersal vectors, and animal behaviour. Certain aspects of HMD have received much attention, such as human-vectored introductions of non-natives [5Ricciardi A. et al.Invasion science: a horizon scan of emerging challenges and opportunities.Trends Ecol. Evol. 2017; 32: 464-474Abstract Full Text Full Text PDF PubMed Scopus (253) Google Scholar] or alteration of landscapes by habitat fragmentation [6Fahrig L. Ecological responses to habitat fragmentation per se.Annu. Rev. Ecol. Evol. Syst. 2017; 48: 1-23Crossref Scopus (525) Google Scholar]. However, these issues tend to be studied in isolation, and there is a lack of a holistic overview of the different aspects of HMD and how they might interact to drive ecological and evolutionary change.Box 1Dispersal Mechanisms and Eco-Evolutionary ProcessesDispersal comprises the movement of individuals or propagules away from their birthplace, leading to reproduction in a new location and generating spatial gene flow. Active dispersal by autonomous movement is governed by the morphology, behaviour, and physiology of an organism. However, organisms can also be dispersed passively by abiotic or biotic vectors, such as animals, wind, or water. In this case, dispersal is determined by traits that affect uptake by the vector and survival during transport. Given that dispersal is an integral part of the life history of an organism, its benefits and costs are correlated with other key life-history traits [39Bonte D. et al.Costs of dispersal.Biol. Rev. 2012; 87: 290-312Crossref PubMed Scopus (807) Google Scholar], which can result in dispersal syndromes [91Beckman N.G. et al.High dispersal ability is related to fast life-history strategies.J. Ecol. 2018; 106: 1349-1362Crossref Scopus (41) Google Scholar]. Dispersal is often described simply in terms of the probability distribution of where dispersing individuals settle relative to the natal sites (i.e., dispersal kernels; [92Bullock J.M. et al.A synthesis of empirical plant dispersal kernels.J. Ecol. 2017; 105: 6-19Crossref Scopus (130) Google Scholar]). However, dispersal is a complex process comprising departure (i.e., leaving the natal location), transfer (movement), and settlement (establishment in the new breeding location). While these processes still result in dispersal kernels, their consideration allows a more mechanistic assessment of dispersal rooted in the movement ecology framework (e.g., [93Nathan R. et al.A movement ecology paradigm for unifying organismal movement research.Proc. Natl. Acad. Sci. 2008; 105: 19052-19059Crossref PubMed Scopus (1705) Google Scholar]). For example, departure can be influenced by local densities, transfer by the resistance to movement in the intervening landscape, and settlement by local cues. This leads to a more eco-evolutionary view of dispersal, whereby dispersal processes and patterns are the result of evolving responses to the (changing) ecological environment [94Delgado M.M. et al.Prospecting and dispersal: their eco-evolutionary dynamics and implications for population patterns.Proc. R. Soc. B Biol. Sci. 2014; 281: 9Crossref Scopus (46) Google Scholar].A particularly interesting area is that of long-distance dispersal (LDD), which is usually characterised in terms of extreme and rare dispersal events [95Jordano P. What is long-distance dispersal? And a taxonomy of dispersal events.J. Ecol. 2017; 105: 75-84Crossref Scopus (103) Google Scholar]. LDD can connect disparate populations, allowing for connectivity and altering interaction networks (see Box 2 in the main text), meaning that it can have profound effects on eco-evolutionary dynamics. Human activities will affect the kernel through the combined effects of the different aspects of HVD and HAD. For example, HVD by automobiles could increase LDD and bias dispersal towards certain directions, while habitat fragmentation (HAD) could at the same time constrain dispersal, such that many dispersers move very short distances: we give an example of the combined effect of these specific processes in Figure I, which ultimately change eco-evolutionary processes. However, the changes to the dispersal kernel in any particular situation will depend on the type and extent of the HVD and HAD processes taking place. Dispersal comprises the movement of individuals or propagules away from their birthplace, leading to reproduction in a new location and generating spatial gene flow. Active dispersal by autonomous movement is governed by the morphology, behaviour, and physiology of an organism. However, organisms can also be dispersed passively by abiotic or biotic vectors, such as animals, wind, or water. In this case, dispersal is determined by traits that affect uptake by the vector and survival during transport. Given that dispersal is an integral part of the life history of an organism, its benefits and costs are correlated with other key life-history traits [39Bonte D. et al.Costs of dispersal.Biol. Rev. 2012; 87: 290-312Crossref PubMed Scopus (807) Google Scholar], which can result in dispersal syndromes [91Beckman N.G. et al.High dispersal ability is related to fast life-history strategies.J. Ecol. 2018; 106: 1349-1362Crossref Scopus (41) Google Scholar]. Dispersal is often described simply in terms of the probability distribution of where dispersing individuals settle relative to the natal sites (i.e., dispersal kernels; [92Bullock J.M. et al.A synthesis of empirical plant dispersal kernels.J. Ecol. 2017; 105: 6-19Crossref Scopus (130) Google Scholar]). However, dispersal is a complex process comprising departure (i.e., leaving the natal location), transfer (movement), and settlement (establishment in the new breeding location). While these processes still result in dispersal kernels, their consideration allows a more mechanistic assessment of dispersal rooted in the movement ecology framework (e.g., [93Nathan R. et al.A movement ecology paradigm for unifying organismal movement research.Proc. Natl. Acad. Sci. 2008; 105: 19052-19059Crossref PubMed Scopus (1705) Google Scholar]). For example, departure can be influenced by local densities, transfer by the resistance to movement in the intervening landscape, and settlement by local cues. This leads to a more eco-evolutionary view of dispersal, whereby dispersal processes and patterns are the result of evolving responses to the (changing) ecological environment [94Delgado M.M. et al.Prospecting and dispersal: their eco-evolutionary dynamics and implications for population patterns.Proc. R. Soc. B Biol. Sci. 2014; 281: 9Crossref Scopus (46) Google Scholar]. A particularly interesting area is that of long-distance dispersal (LDD), which is usually characterised in terms of extreme and rare dispersal events [95Jordano P. What is long-distance dispersal? And a taxonomy of dispersal events.J. Ecol. 2017; 105: 75-84Crossref Scopus (103) Google Scholar]. LDD can connect disparate populations, allowing for connectivity and altering interaction networks (see Box 2 in the main text), meaning that it can have profound effects on eco-evolutionary dynamics. Human activities will affect the kernel through the combined effects of the different aspects of HVD and HAD. For example, HVD by automobiles could increase LDD and bias dispersal towards certain directions, while habitat fragmentation (HAD) could at the same time constrain dispersal, such that many dispersers move very short distances: we give an example of the combined effect of these specific processes in Figure I, which ultimately change eco-evolutionary processes. However, the changes to the dispersal kernel in any particular situation will depend on the type and extent of the HVD and HAD processes taking place. Here, we show how HMD is expected to have complex effects on spatial networks (Box 2) of populations and communities and we demonstrate the benefits of considering the variety of HVD and HAD processes in combination. First, we review the different forms of HVD and HAD and consider the types of organism and community that are affected by these processes. Humans have probably mediated dispersal throughout our history, and there is evidence that early humans and preindustrial societies changed the distributions of species [7Boivin N.L. et al.Ecological consequences of human niche construction: examining long-term anthropogenic shaping of global species distributions.Proc. Natl. Acad. Sci. 2016; 113: 6388-6396Crossref PubMed Scopus (405) Google Scholar, 8Levis C. et al.Persistent effects of pre-Columbian plant domestication on Amazonian forest composition.Science. 2017; 355: 925-931Crossref PubMed Scopus (308) Google Scholar], and that humans have performed important ecosystem functions more generally [9Bliege Bird R. Nimmo D. Restore the lost ecological functions of people.Nat. Ecol. Evol. 2018; 2: 1050-1052Crossref PubMed Scopus (51) Google Scholar]. However, human activities are undergoing rapid expansion in scope and spatial extent: the human footprint extends over 75% of the global land area [10Venter O. et al.Sixteen years of change in the global terrestrial human footprint and implications for biodiversity conservation.Nat. Commun. 2016; 7: 11Crossref Scopus (814) Google Scholar], and it is intensifying rapidly both on land and in the sea [10Venter O. et al.Sixteen years of change in the global terrestrial human footprint and implications for biodiversity conservation.Nat. Commun. 2016; 7: 11Crossref Scopus (814) Google Scholar, 11Watson R.A. et al.Marine foods sourced from farther as their use of global ocean primary production increases.Nat. Commun. 2015; 6: 6Crossref Scopus (69) Google Scholar]. Consequently, below we present evidence that increasing HMD leads to radical changes in the structure and functioning of spatial networks, and causes the rewiring of spatial interactions from genes to ecosystems (Figure 1). Considered in this integrated manner, the impact of HMD reaches beyond the introduction of non-native species by also changing ecological and evolutionary dynamics in native regions. We then draw conclusions about the benefits of studying HMD in a holistic manner. We do not cover HMD of human diseases, which has specific attributes and has been the topic of many studies, as reviewed in [12Funk S. et al.Modelling the influence of human behaviour on the spread of infectious diseases: a review.J. R. Soc. Interface. 2010; 7: 1247-1256Crossref PubMed Scopus (770) Google Scholar].Box 2Spatial Ecological NetworksBiological communities can be envisioned as local interaction networks [96Bascompte J. Jordano P. Mutualistic Networks. Princeton University Press, 2014Crossref Google Scholar], with species represented as nodes and interactions as links and defined within a finite spatial extent (e.g., sites or habitat patches; see Figure 3 in the main text). Antagonistic and mutualistic interaction frequencies depend on both the relative abundances of species (with more abundant species showing higher interaction probabilities) and the matching of traits fostering interactions (e.g., long-tongued insects with long-corolla flowers). The local interaction networks are organised over larger spatial extents by species-specific routine movement (spatial coupling) or dispersal (metapopulations and metacommunities). Spatial coupling occurs within generations and is typically mediated by resource-acquisition strategies, either foraging or mate search. Metapopulation and metacommunity dynamics emerge from dispersal, and generate changes in patch occupancy and abundances at these larger scales. The strength of the spatial interactions are determined by the specific dispersal rates, which generally decline with increased distance and landscape resistance (see Box 1 in the main text), and the abundances of species in the source population. Dispersal determines the presence and/or abundance of local species and gene flow, but local competition, predation, or mutualism interactions in the metacommunity will in turn impact dispersal [97Bonte D. Dahirel M. Dispersal: a central and independent trait in life history.Oikos. 2017; 126: 472-479Crossref Scopus (112) Google Scholar]. Therefore, the spatial and local topology of ecological networks is likely to be coupled nonlinearly through eco-evolutionary dynamics.The dynamical properties of the spatial network are typically analysed using matrix models that combine Lotka-Volterra formulations of species interactions with species-specific among-patch dispersal rates [80Melián C.J. et al.Deciphering the interdependence between ecological and evolutionary networks.Trends Ecol. Evol. 2018; 33: 504-512Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar] or through aggregated food-chain approaches [98Pillai P. et al.Metacommunity theory explains the emergence of food web complexity.Proc. Natl. Acad. Sci. 2011; 108: 19293-19298Crossref PubMed Scopus (125) Google Scholar]. Evolutionary dynamics can be integrated by adding gene interaction networks to produce dynamic local trait distributions that determine interspecific interaction strengths. However, the eco-evolutionary approach is still in its infancy because it relies on a comprehensive understanding of the genetic architecture underlying trait distribution and its connection to species interactions [80Melián C.J. et al.Deciphering the interdependence between ecological and evolutionary networks.Trends Ecol. Evol. 2018; 33: 504-512Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar].Spatial ecological networks can be altered by both human-driven changes in the local interaction network among species and changes in dispersal interactions among patches. Given that the stability of the spatial interaction network depends on the distribution of interaction strengths [99François M. et al.Linking community and ecosystem dynamics through spatial ecology.Ecol. Lett. 2011; 14: 313-323Crossref PubMed Scopus (179) Google Scholar], any selection exerted by HMD on traits of species and genotypes that mediate interaction strengths will strongly impact this stability. This topological complexity eventually determines the robustness and resilience, and, ultimately, the ecosystem functioning of the entire spatial network. To what degree the hierarchical integration of gene interactions changes this view is currently an open question. Biological communities can be envisioned as local interaction networks [96Bascompte J. Jordano P. Mutualistic Networks. Princeton University Press, 2014Crossref Google Scholar], with species represented as nodes and interactions as links and defined within a finite spatial extent (e.g., sites or habitat patches; see Figure 3 in the main text). Antagonistic and mutualistic interaction frequencies depend on both the relative abundances of species (with more abundant species showing higher interaction probabilities) and the matching of traits fostering interactions (e.g., long-tongued insects with long-corolla flowers). The local interaction networks are organised over larger spatial extents by species-specific routine movement (spatial coupling) or dispersal (metapopulations and metacommunities). Spatial coupling occurs within generations and is typically mediated by resource-acquisition strategies, either foraging or mate search. Metapopulation and metacommunity dynamics emerge from dispersal, and generate changes in patch occupancy and abundances at these larger scales. The strength of the spatial interactions are determined by the specific dispersal rates, which generally decline with increased distance and landscape resistance (see Box 1 in the main text), and the abundances of species in the source population. Dispersal determines the presence and/or abundance of local species and gene flow, but local competition, predation, or mutualism interactions in the metacommunity will in turn impact dispersal [97Bonte D. Dahirel M. Dispersal: a central and independent trait in life history.Oikos. 2017; 126: 472-479Crossref Scopus (112) Google Scholar]. Therefore, the spatial and local topology of ecological networks is likely to be coupled nonlinearly through eco-evolutionary dynamics. The dynamical properties of the spatial network are typically analysed using matrix models that combine Lotka-Volterra formulations of species interactions with species-specific among-patch dispersal rates [80Melián C.J. et al.Deciphering the interdependence between ecological and evolutionary networks.Trends Ecol. Evol. 2018; 33: 504-512Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar] or through aggregated food-chain approaches [98Pillai P. et al.Metacommunity theory explains the emergence of food web complexity.Proc. Natl. Acad. Sci. 2011; 108: 19293-19298Crossref PubMed Scopus (125) Google Scholar]. Evolutionary dynamics can be integrated by adding gene interaction networks to produce dynamic local trait distributions that determine interspecific interaction strengths. However, the eco-evolutionary approach is still in its infancy because it relies on a comprehensive understanding of the genetic architecture underlying trait distribution and its connection to species interactions [80Melián C.J. et al.Deciphering the interdependence between ecological and evolutionary networks.Trends Ecol. Evol. 2018; 33: 504-512Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. Spatial ecological networks can be altered by both human-driven changes in the local interaction network among species and changes in dispersal interactions among patches. Given that the stability of the spatial interaction network depends on the distribution of interaction strengths [99François M. et al.Linking community and ecosystem dynamics through spatial ecology.Ecol. Lett. 2011; 14: 313-323Crossref PubMed Scopus (179) Google Scholar], any selection exerted by HMD on traits of species and genotypes that mediate interaction strengths will strongly impact this stability. This topological complexity eventually determines the robustness and resilience, and, ultimately, the ecosystem functioning of the entire spatial network. To what degree the hierarchical integration of gene interactions changes this view is currently an open question. HVD is the direct dispersal of organisms by human actions, either intentionally or accidentally (Figure 2). Intentional HVD not only comprises the transport of organisms for human use in agriculture, horticulture, hunting, biocontrol, ornamental use, or to be kept as pets, but also includes translocation for conservation purposes [13Seddon P.J. et al.Reversing defaunation: restoring species in a changing world.Science. 2014; 345: 406-412Crossref PubMed Scopus (393) Google Scholar]. Accidental HVD can be by attachment to humans [14Wichmann M.C. et al.Human-mediated dispersal of seeds over long distances.Proc. R. Soc. B Biol. Sci. 2009; 276: 523-532Crossref PubMed Scopus (135) Google Scholar] or on and in entities moved physically by humans, such as vehicles [15Weiss F. et al.Mountain bikes as seed dispersers and their potential socio-ecological consequences.J. Environ. Manag. 2016; 181: 326-332Crossref PubMed Scopus (16) Google Scholar], pets [16Koch K. et al.A voyage to Terra Australis: human-mediated dispersal of cats.BMC Evol. Biol. 2015; 15: 262Crossref PubMed Scopus (21) Google Scholar], ornamental and cultivated plants [17Chapman D. et al.Global trade networks determine the distribution of invasive non-native species.Global Ecol. Biogeogr. 2017; 26: 907-917Crossref Scopus (126) Google Scholar], livestock [18Auffret A.G. Can seed dispersal by human activity play a useful role for the conservation of European grasslands?.Appl. Veg. Sci. 2011; 14: 291-303Crossref Scopus (46) Google Scholar], human introduction of wild animals [19Simberloff D. Von Holle B. Positive interactions of nonindigenous species: invasional meltdown?.Biol. Invasions. 1999; 1: 21-32Crossref Scopus (1562) Google Scholar], and human products and food [20Valls L. et al.Human-mediated dispersal of aquatic invertebrates with waterproof footwear.Ambio. 2016; 45: 99-109Crossref PubMed Scopus (23) Google Scholar] (Figure 2C). We differentiate the movement of animals by humans (HVD; e.g., livestock herding or pet transport) from the self-willed movement of animals managed or introduced by humans (e.g., free-roaming livestock or escaped introduced species, which is HAD). HVD is most studied in plants and animals, but human transport of other organisms such as fungi [21Golan J.J. Pringle A. Long-distance dispersal of fungi.Microbiol. Spectr. 2017; 5: 24Google Scholar] and protists [22Perrigo A.L. et al.What's on your boots: an investigation into the role we play in protist dispersal.J. Biogeogr. 2012; 39: 998-1003Crossref Scopus (13) Google Scholar] has also been demonstrated. For organisms to undergo HVD, they first need to be exposed to human contact and be taken up (e.g., attached or captured) for departure (Figure 1). Therefore, HVD will only occur in areas where humans are either resident or travelling through. This already encompasses most of the globe [10Venter O. et al.Sixteen years of change in the global terrestrial human footprint and implications for biodiversity conservation.Nat. Commun. 2016; 7: 11Crossref Scopus (814) Google Scholar, 11Watson R.A. et al.Marine foods sourced from farther as their use of global ocean primary production increases.Nat. Commun. 2015; 6: 6Crossref Scopus (69) Google Scholar], but as human populations and frequency of movement increase, HVD will become more common, facilitated by a greater number and density of, for example, road networks, urban areas, and shipping routes [23Miller A.W. Ruiz G.M. Arctic shipping and marine invaders.Nat. Clim. Change. 2014; 4: 413Crossref Scopus (111) Google Scholar, 24Auffret A.G. et al.The geography of human-mediated dispersal.Divers. Distrib. 2014; 20: 1450-1456Crossref Scopus (34) Google Scholar] (Figure 2A). The subsequent patterns of transfer and settlement (Box 1) and, thus, the shape and extent of dispersal kernels, will be affected by the specific HVD process. Some forms of HVD permit settlement during human transit, by active or passive deposition of individuals along the transport network. For instance, seeds attached to hikers will generally be transported along walking routes, but could detach at any point on the path. The resulting dispersal kernels often resemble those caused by attachment to animals [25Bullock J.M. et al.Process-based functions for seed retention on animals: a test of improved descriptions of dispersal using multiple data sets.Oikos. 2011; 120: 1201-1208Crossref Scopus (25) Google Scholar] and patterns along the network will exhibit simple distance decay. By contrast, other forms of HVD have low probabilities of settlement during human transit (e.g., organisms in ballast water or ornamental plants in lorries) and will mainly settle at nodes of the transport network (ports, cities, etc.), causing discontinuous dispersal patterns dominated by long-distance jumps. Furthermore, much contemporary human travel behaviour might best be described as a continuous random-walk process, incorporating long time lags between movements and scale-free jumps [26Brockmann D. et al.The scaling laws of human travel.Nature. 2006; 439: 462-465Crossref PubMed Scopus (1596) Google Scholar]. The dispersal kernels resulting from this behaviour are likely to contrast strongly with the unimodal, distance decay form of many natural dispersal kernels (Box 1). Such dispersal might best be described by gravity models, which can capture how human movement patterns reflect not only distance, but also changed patterns caused by travel between 'attractive' nodes, such as cities [27Jongejans E. et al.A unifying gravity framework for dispersal.Theor. Ecol. 2015; 8: 207-223Crossref Scopus (19) Google Scholar]. Long-distance dispersal (i.e., the tail of the dispersal kernel) has particularly important consequences for ecology and evolution (Box 1), and several studies have demonstrated longer distance dispersal under HVD than through natural processes. These include seeds travelling over 20 times further by attachment to hiking boots compared with dispersal by wind [14Wichmann M.C. et al.Human-mediated dispersal of seeds over long distances.Proc. R. Soc. B Biol. Sci. 2009; 276: 523-532Crossref PubMed Scopus (135) Google Scholar], dispersal of an invasive fish in ballast water 400 times further than the maximum under natural movement [28Johansson M.L. et al.Human-mediated and natural dispersal of an invasive fish in the eastern Great Lakes.Heredity. 2018; 120: 533-546Crossref PubMed Scopus (17) Google Scholar], and transport of marine invertebrates by shell fisheries ten times further than their maximum distances as plankton [29Woodin S.A. et al.Population structure and spread of the polychaete Diopatra biscayensis along the French Atlantic coast: human-assisted transport by-passes larval dispersal.Mar. Environ. Res. 2014; 102: 110-121Crossref PubMed Scopus (16) Google Scholar]. While the characteristics of human movement make it likely that dispersal distances will be increased under HVD, it is not a given that HVD will always lead to long-distance dispersal (Figure 2B). The outcome depends on the HVD process, and the resulting distances can be shorter than under natural dispersal [30von der Lippe M. et al.Human-mediated dispersal of seeds by the airflow of vehicles.PLoS One. 2013; 8e52733Crossref PubMed Scopus (96) Google Scholar]. The propensity of a species for HVD will be determined largely by traits that affect uptake and retention by the human vec