Question

How is an invasive species introduced?

Answer 1

Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions.
CHeck the gov site: http://www.invasivespeciesinfo.gov/whatis.shtml

Answer 2

Pathways are the means by which species are transported from one location to another. Natural pathways include wind, currents, and other forms of dispersal in which a specific species has developed morphological and behavioral characteristics to employ.

Man-made pathways are those pathways which are enhanced or created by human activity. These are characteristically of two types.

Answer 3

Also from the NISC site.