Invasion of North American drainages by alien fish species

1. Data from the literature were used to document colonization patterns by introduced freshwater fishes in 125 drainages across temperate North America. We analysed this data set to quantify susceptibility to invasion, success of the invaders and changes in species richness. 2. Drainages with a high number of impoundments, large basin area and low native species diversity had the greatest number of introduced species. Those drainages containing few native fishes exhibited great variation in the number of invaders, while waters with a rich native fauna contained few introduced species. However, this pattern did not differ significantly from random simulations because the pool of potential invaders is greater for drainages with low species richness. 3. In most drainages, there were more introduced than imperilled or extirpated species, suggesting that invaders tend to increase overall species richness. 4. These patterns suggest that North American fish communities are not saturated with species, but instead, are capable of supporting higher levels of diversity if the pool of potential colonists and the rate of colonization from that pool is increased.