How do invasive species travel to and through urban environments?
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Globalisation has resulted in the movement of organisms outside their natural range, often with negative ecological and economic consequences. As cities are hubs of anthropogenic activities, with both highly transformed and disturbed environments, these areas are often the first point of entry for alien species. We compiled a global database of cities with more than one million inhabitants that data had on alien species occurrence. We then identified the most prominent pathways of introduction and vectors of spread of alien species in these cities. Most species were intentionally introduced to cities and were released or escaped from confinement. The majority of alien species then spread within cities through natural means (primarily unaided dispersal). Pathway prominence varied across the taxonomic groups of alien species: the most prominent pathway for plants and vertebrates was the escape pathway; for invertebrates the stowaway and contaminant pathways were most likely to facilitate introductions. For some organisms, pathway prominence varied with the geographical and climatic characteristics of the city. The characteristics of the cities also influenced the prominence of vectors of spread for alien species. Preventing the natural spread of alien species within cities, and into adjacent natural environments will be, at best, difficult. To prevent invasions, both the intentional and unintentional introduction of potentially harmful alien species to cities must be prevented. The pathways of introduction and vectors of spread identified here should be prioritised for management.
KeywordsBiological invasions Pathways of introduction Prioritisation Urban invasions Vectors of spread
This research was funded by the South African National Department of Environmental Affairs through its funding of the South African National Biodiversity Institute’s Invasive Species Programme. An early version of this paper was presented at a workshop on “Non-native species in urban environments: Patterns, processes, impacts and challenges” that was hosted and co-funded by the DST-NRF Centre of Excellence for Invasion Biology in Stellenbosch in November 2016. Many participants at the workshop provided useful comments and suggestions which improved the paper. We thank The Global Invasive Species Database for the provision of data, Desika Moodley and Osadolor Ebhuoma for their technical assistance, and two anonymous reviewers for their comments and suggestions.
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