Clothing, footwear and possessions (pathway vector)
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Clothing, footwear and possessions (pathway vector)
International Common Names
- English: human epizoochory; human-mediated dispersal (HMD)
OverviewTop of page
Being attached to an individual person’s clothing or footwear is never the only means by which a plant is dispersed, and is unlikely even to ever be the most important means. It is a secondary means at most; more commonly a minor one. It will also be primarily involved in local spread, and only in exceptional circumstances, in international introductions. However, it has been shown to be important in specific areas where other pathways are uncommon, such as uninhabited islets, e.g. in the Galapagos and the sub-Antarctic where frequently visiting researchers are a significant risk (Whinam et al., 2005) or national parks or other protected areas with a regular inflow of (eco) tourists.
DescriptionTop of page
Summary of organism types or species introduced
Many invasive plants could be inadvertently transported by individual people, and thorough research could unearth very many examples. This datasheet presents 21 examples of plant species that have been recorded as likely or possibly dispersed by attaching themselves to clothes and footwear.
Emex australis and Emex spinosa have hard, thorny achenes that lie on the ground so that one thorn is always pointing upwards. They share the common name 'three-corner jack' and the spines are slightly reflexed so that they can hook onto passing objects, and the erect habit of the plant would encourage dissemination by this method. Attachment of the achenes to the tyres of vehicles, aircraft and machinery is the main method of spread, and allows the seeds to be transported long distances, though they are also dispersed on the soles of shoes (Lemerle, 1996). The spines of E. spinosa are shorter and less robust than those of E. australis, which may explain the slower rates of spread of E. spinosa within Australia. Although E. spinosa achenes are less likely than E. australis achenes to impale and then remain attached to broad, flat rubber surfaces such as the soles of shoes, their smaller size allows them to wedge between the treads of shoes and tyres.
The spiny fruits of the false puncture vine (Tribulus cistoides) are well equipped for dispersal by wild and domestic animals, and also on human clothes and footwear. The large and small spines on the fruit are arranged at different angles so that, no matter how the seed falls, one of the spines always points upward to meet the unwary foot, hoof or vehicle tyre (Holm et al., 1977) which gives rise to another common name, 'caltrop', the spiked metal ball thrown under the feet of horses in mediaeval warfare. The common puncture vine (Tribulus terrestris) may have been disseminated across the world in the wool of European sheep (Holm et al., 1977) and could also be carried on clothes or shoes.
Seed of garlic mustard (Alliaria petiolata) is transported by humans, potentially great distances, through mud on the soles of shoes. This is indicated by the observations of A. petiolata at woodland and park entrances, and its lining the edges of footpaths and woodland hiking trails in parts of North America.
Cheatgrass or downy brome (Bromus tectorum) has barbs on the lemma, palea and awns which are very effective in aiding seed dispersal, seeding in animal fur and also human clothing, especially in socks (WSSA, 2003).
The burs of southern sandbur (Cenchrus echinatus) seed heads can become firmly attached to clothes and the coats of animals by the barbed spines (Cardenas et al., 1972).
Seeds of several thistles such as Cirsium arvense can be carried to new locations by sticking to the clothes and shoes of humans, and to the fur and feet of animals (Holm et al., 1991).
The common ragwort (Senecio jacobaea) is reported to be dispersed by 'humans and their animals' (Schmidl, 1972) and S. vulgaris is also transported attaching itself to clothes, shoes, etc. (McHenry et al., 1990).
The seeds of crofton weed (Ageratina adenophora) are known to attach themselves, often in mud, to clothes of agricultural workers as well as tourists, hikers, and especially to farm machinery.
Two knapweeds, Centaurea diffusa and Centaurea stoebe subsp. micranthos, are considered to have been spread by attaching themselves to shoes in North America (Watson and Renney, 1974).
Dispersal of the common or Scotch broom (Cytisus scoparius) and the Montpellier broom (Genista monspessulana) is thought to occur by the movement of seed in mud attached to all-terrain vehicles and ramblers' boots (Parsons and Cuthbertson, 1992; Peterson and Prasad, 1998).
The leafy spurge (Euphorbia esula) can be spread by casual contact and dispersed by human activity, and soils contaminated by leafy spurge seeds may adhere to shoes, cars and farming equipment. The ripe fruits of the sun spurge (Euphorbia helioscopia) split explosively to scatter seeds around the plant, from where they may be further spread in irrigation and flood waters, in mud on vehicles, boots and animals and in plant trash, hay and straw.
Seeds of Senna occidentalis can be spread in mud sticking to animal hooves, footwear, farm machinery and other vehicles (Parsons and Cuthbertson, 1992).
Seed of the prostrate knotweed (Polygonum aviculare) may be dispersed in mud on footwear or tyre treads (Grime et al., 1988).
Dog fennel (Anthemis cotula) achenes may occur in mud or soil caked onto animal hooves or hide, in the cuffs of trousers, or in animal faeces (Kay, 1971) though these are not considered common means of dispersal.
The seeds of purple loosestrife (Lythrum salicaria) are likely to be dispersed in mud adhering to aquatic wildlife or via consumption by waterfowl, or attached to livestock, all-terrain vehicle tyres and human footwear, although there is no direct evidence to support any of these potential pathways (Thompson et al., 1987).
Humans are also thought to be minor dispersal agents of seeds or achenes of Siam weed (Chromolaena odorata).
Fruit or seed have generally evolved one of a number of specific adaptations, such as hooks on part of the fruit itself, or fruit that are covered by a persistent calyx equipped with hooks or persistent styles with hooked tips. Seeds that fall into trouser turn-ups or are stuck in mud to clothes or footwear need no such characteristics, however. Some species have a form or habit that appears well-adapted to promoting adhesion to passing animals (humans now included) such as an erect form and position of the fruits.
The ability to stay attached is also important to guarantee the distance travelled. Wichmann et al. (2009) studied how many seeds are carried by humans on shoes of two plant species. Over half of all seeds fell off within 5 m, but some were regularly still attached to shoes after 5 km. Semi-mechanistic models suggested primary dispersal by wind and secondary dispersal by humans, and that walking humans can disperse seeds to very long distances, up to at least 10 km.
Geographical routes and corridors
On a local scale, corridors follow footpaths, tracks, roads, etc. They also follow the 'paths' of ecologists, researchers or eco-tourists, which could be considered as a significant subset of people responsible for epihomochory.
Humans have inadvertently carried seeds on their hair, hides, clothes and footwear since the earliest times. However, the scale of this has increased with a greater number of people travelling ever-greater distances, but it still remains only a minor means of plant introduction and spread.
Species Transported by VectorTop of page
ManagementTop of page
The accidental spread of plants within an area by people may be unavoidable. However, impacts can be made to reduce the risk of introduction to new areas. Inspection surveys need to be made to assess the level of risk, such as were carried out on people travelling to remote sub-Antarctic locations by Whinam et al. (2005). Following this work, changes were implemented regarding management and logistical arrangement to reduce the risks, which have proved effective.
Other studies have made similar recommendations regarding simple checks and hygiene, such as Venner (2007) who suggested that road workers carefully remove any plant material from their clothes and footwear to avoid the risk of introduction of invasive species to new areas. Awareness raising is one of the most common means, by educating visitors about the risks and how they can reduce them. Many national parks and protected areas include such warnings on their websites and brochures, asking people to ensure that they have cleaned the mud off their walking boots or shoes, and to check their clothes for the presence of attached seeds, etc. Instituting more checks on individuals at key entry points would be more costly, but more effective. These could be airports, ports, the gates to national parks, etc.
ReferencesTop of page
Cardenas J; Reyes CE; Doll JD, 1972. Tropical weeds Vol. 1. Bogota, Colombia: Instituto Colombiano Agropecuario.
Kay QON, 1971. Biological flora of the British Isles. Anthemis cotula L. Journal of Ecology, 59:623-636.
Kerr S; Cardenas S; Hendy J, 2004. Migration and the environment in the galapagos: an analysis of economic and policy incentives driving migration, potential impacts from migration control, and potential policies to reduce migration pressure. Motu Working Paper Series, No. 03-17. Wellington, New Zealand: Motu (Economic Research and Public Policy), 188pp.
McHenry WB; Bushnell RB; Oliver MN and Norris RF, 1990. Three poisonous plants common in pasture and hay: fiddleneck, common groundsel, yellow starthistle. University of California Cooperative Extension Publ. 21483, Berkeley, CA.
Schmidl L, 1972. Biology and control of ragwort, Senecio jacobaea L., in Victoria, Australia. Weed Research, 12:37-45.
Thompson DQ; Stuckey RL; Thompson EB, 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. United States Fish and Wildlife Service, Fish and Wildlife Research No.2. Washington DC, USA: United States Department of the Interior.
Whinam J; Chilcott N; Bergstrom DM, 2005. Subantarctic hitchhikers: expeditioners as vectors for the introduction of alien organisms. Biological Conservation, 121(2):207-219. http://www.sciencedirect.com/science/journal/00063207
Wichmann MC; Alexander MJ; Soons MB; Galsworthy S; Dunne L; Gould R; Fairfax C; Niggemann M; Hails RS; Bullock JM, 2009. Human-mediated dispersal of seeds over long distances. Proceedings of the Royal Society of London. Series B, Biological Sciences, No.1656:523-532. http://publishing.royalsociety.org/index.cfm?page=1569
WSSA, 2003. 1,000 weeds of North America: an identification guide. Lawrence, USA: Weed Science Society of America.
ContributorsTop of page
6/30/2009 Original text by:
Nick Pasiecznik, Consultant, France