After J. L. Lockwood, P. Cassey and T. Blackburn (2009, Diversity and Distributions, 15, 904–910) first described a theoretical relationship between propagule pressure and colonization pressure, two empirical studies demonstrated that the transport stage of the invasion process can profoundly influence the strength of the relationship among multiple events, as well as predictions of introduction risk. However, studies exploring dynamics of transported communities are rare, as repeated-measures sampling during transportation by any vector is logistically difficult. We constructed a conceptual model of community dynamics during transportation and supported it by empirical data for propagule pressure and colonization pressure of plankton.
A conceptual model of community dynamics was developed based on lognormal species abundance distribution and the simulation model of J. L. Lockwood, P. Cassey and T. Blackburn (2009, Diversity and Distributions, 15, 904–910). We considered four cases: case ‘A’ – no reduction in propagule nor colonization pressure; case ‘B’ – strong reduction in propagule and mild reduction in colonization pressure; case ‘C’ – mild reduction in propagule and strong reduction in colonization pressure; and case ‘D’ – strong reduction in both propagule and colonization pressures.
The cases ‘B’, ‘C’ and ‘D’ were supported by empirical data for invertebrates, dinoflagellates and diatoms from ships’ ballast tanks, respectively. Propagule pressure of invertebrates, dinoflagellates and diatoms decreased 99.95%, 80% and 94% in 25 days, respectively, while colonization pressure decreased 34%, 57% and 64%.
Transport affects both propagule pressure and colonization pressure of taxa, with the magnitude of change dependent on length of transport and taxon-specific survival and reproduction. Our model demonstrates that introduction risk varies substantially across and within taxa depending on the occurrence and severity of selection pressures during transportation which serve to change species abundance distributions.