ABSTRACT:

Invasion dynamics are influenced by both vector operation and propagule pressure. Which propagules are entrained in a vector depends on how, where, and when a vector operates, but the timing and effects of vector operations on species delivery patterns is poorly resolved. Using the live marine baitworm trade, we tested vector selectivity across 3 boreal seasons (summer 2011, fall 2011, and spring 2012). We compared macroinvertebrate assemblages at the source (Maine, US east coast field) and in baitboxes upon delivery (Mid-Atlantic distributors, US east coast) and quantified live and dead biota to test for interactive effects of season and vector stage (i.e. source vs. destination) on per capita abundance, species richness, diversity, functional richness, and community composition. In all, we identified 46262 hitchhiking macro-organisms from 56 distinct taxa. Among live biota, taxonomic richness, functional group richness, and abundance differed by vector stage and season. Community composition showed seasonality for functional groups, but not for taxonomic groups. Vector stage affected dead community composition more than season, implying that vector operations (i.e. handling at source and during shipping) filter species transfers differentially. Dead communities were typically composed of the most abundant live organisms in the same baitboxes, emphasizing how important propagule pressure is to successful transport. Some combinations of 5 key functional traits (body size, feeding mode, growth form, modularity, and motility) were associated with increased survival during vector transfer. Successful species transfers are correlated with specific functional traits and propagule pressure, both of which are influenced by seasonal variation.