Abstract
BackgroundUnderstanding the dimensions of pathways of introduction of alien plants is important for regulating species invasions, but how particular pathways differ in terms of post-invasion success of species they deliver has never been rigorously tested. We asked whether invasion status, distribution and habitat range of 1,007 alien plant species introduced after 1500 A.D. to the Czech Republic differ among four basic pathways of introduction recognized for plants.Principal FindingsPathways introducing alien species deliberately as commodities (direct release into the wild; escape from cultivation) result in easier naturalization and invasion than pathways of unintentional introduction (contaminant of a commodity; stowaway arriving without association with it). The proportion of naturalized and invasive species among all introductions delivered by a particular pathway decreases with a decreasing level of direct assistance from humans associated with that pathway, from release and escape to contaminant and stowaway. However, those species that are introduced via unintentional pathways and become invasive are as widely distributed as deliberately introduced species, and those introduced as contaminants invade an even wider range of seminatural habitats.ConclusionsPathways associated with deliberate species introductions with commodities and pathways whereby species are unintentionally introduced are contrasting modes of introductions in terms of invasion success. However, various measures of the outcome of the invasion process, in terms of species' invasion success, need to be considered to accurately evaluate the role of and threat imposed by individual pathways. By employing various measures we show that invasions by unintentionally introduced plant species need to be considered by management as seriously as those introduced by horticulture, because they invade a wide range of seminatural habitats, hence representing even a greater threat to natural areas.
Highlights
The past decade has seen much research focused on practical issues of biological invasions, such as the impact of invasive species [1,2,3,4], and on scientific topics generating knowledge that can be used to predict and regulate their introductions [5,6]
Pathways associated with deliberate species introductions with commodities and pathways whereby species are unintentionally introduced are contrasting modes of introductions in terms of invasion success
Various measures of the outcome of the invasion process, in terms of species’ invasion success, need to be considered to accurately evaluate the role of and threat imposed by individual pathways
Summary
The past decade has seen much research focused on practical issues of biological invasions, such as the impact of invasive species [1,2,3,4], and on scientific topics generating knowledge that can be used to predict and regulate their introductions [5,6]. Pathways are defined as a suite of processes that result in the introduction of an alien species from one geographical location to another, and vectors include dispersal mechanisms and means of introduction [11] Good knowledge of both these categories provides options for limiting contamination of vectors (e.g., through control of pest populations in source regions), monitoring pathways for target pests, and generic management measures that may have added benefits beyond the target pest species (e.g., machinery cleaning, contaminant control, hull cleaning and antifouling, ballast water exchange). Such interventions have the potential for reducing propagule pressure [12,13,14,15] and the likelihood of establishment and spread. We asked whether invasion status, distribution and habitat range of 1,007 alien plant species introduced after 1500 A.D. to the Czech Republic differ among four basic pathways of introduction recognized for plants
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