Changes in global economies and trade: the potential spread of exotic freshwater bivalves

The globalization of economies and trade have facilitated the spread of exotic species including the five most important freshwater suspension feeding invaders Dreissena polymorpha, D. bugensis, Corbicula fluminea, C fluminea, and Limnoperna fortunei. We suggest that the spread of these exotic species has not been a continuous process, but rather punctuated by periods of rapid long distance spread (jump), during which species greatly expanded their geographic ranges. Each jump has been associated with changes in the tempo of some human activity, such as the construction of shipping canals for trade, building of reservoirs for water storage and power production, political boundary changes or changes in political systems, which affected the position or permeability of national borders, human migration, changes in the mode and volume of international trade, or recent industrial practices and environmental laws. We hypothesize that the rate of spread of exotic species depends on the spatial scale of spread and may be accelerated or slowed by various human activities. In general, aquatic exotic species may quickly spread along connected waterways in a new continent they invade and soon reach their maximum range (continental scale). However, it will take much longer to colonize all isolated regions (regional scale) and longer still to spread to all isolated lakes and river systems (local scale). The difference in the rate of colonization across scales may be several orders of magnitude.