Residence Time

Not only biological traits of species are important. Cultural influence has been recognized as an important factor co determining the fate of species subsequent to their first introduction to a new area. Stochastic effects, which depend on initial inoculum size, residence time, chance events, and the number of introduction events (propagule pressure) and their spatial distribution, co determine whether a species becomes invasive. A key generalization is that the probability of invasion increases with residence time, that is, the time since the introduc tion of a taxon to a new area. Residence time itself is a dimension of propagule pressure: the longer the residence time, the region, the more propagules are produced and dispersed, and the greater the chances of new populations be established. The positive relationship between current geographical distribution and/or frequency of alien species and their residence time has been documented for a number of regions as well as for individual species at different scales. In Europe, the effect of residence time is still obvious after several millennia of plant invasions. Those archeophytes that invaded soon after the beginning of Neolithic agriculture are more common and have wider distribution ranges than those that arrived later.

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