Abstract
Understanding the mechanisms that support the arrival, establishment and spread of species over an introduced range is crucial in invasion ecology. We analysed the unintentionally introduced herbaceous species that are naturalised in the five Mediterranean-climate regions. There is an asymmetry in the species flows among regions, being the Iberian Peninsula the main donor to the other regions. At interregional scale, the species’ capacity to spread among regions is related to the ecological versatility of the species in the donor area (Iberian Peninsula). At intraregional scale, the species’ capacity to successfully occupy a complete region first depends on the time elapsed from its introduction and afterwards on the degree of occurrence in the region of origin, which is commonly related to its chance of coming into contact with humans. Information on exotic species in their origin region provides insights into invasion process and decision-making to reduce the risks of future invasions.
Highlights
The geographical transport of species associated with human activity has increased with time, currently presenting unprecedented levels[1]
Asymmetries in species flows can occur among different subsets of species, often because given life forms are associated with one specific introduction pathway
In order to reduce the factors that may have influenced the invasiveness of the species, we have only considered the unintentional pathway species, which represent more than 80% of the exotic species in MCRs30
Summary
The geographical transport of species associated with human activity has increased with time, currently presenting unprecedented levels[1]. Very few of these characteristics have revealed consistent patterns[12], and their capacity for prediction has been questioned[6,8,13,14] Likewise, extrinsic factors such as environmental heterogeneity, time since introduction[5], propagule pressure[15,16] or human disturbance[17,18] have been proposed to explain the geographical extent of plant invaders. Asymmetries in species flows between countries or regions may be associated with historical[21], commercial[22] or economic[23] factors These factors are important in the case of deliberate introductions (release into nature, escape from confinement) where human being is responsible for their transport, and provides assistance for them to become established and to spread[24,25]. On the other hand, quantifying the number of naturalized exotic species and their potential for expansion at the regional level (potential regional spread) can more clearly shed light on the processes of plant invasion at the global level
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