Plotting the course of an African clawed frog invasion in Western France

The African clawed frog, Xenopus laevis, is an invasive species with considerable impact in mediterranean climates, similar to its native South African Cape. A population has been established in western France since the early 1980s with a single, known, original release point. This study attempts to determine the limits of the invasion by trapping in 169 ponds in 2001 and 2002. Subsequent trapping of 192 ponds in 2003 and 2004 was undertaken in order to chart the progress of invasion, and to test the hypothesis that ponds were mostly colonised using rivers and streams as corridors. Of ponds without X. laevis in 2001/2002, 36% were found to have been colonised by 2003/2004. The findings clearly show that, while lotic corridors are used by this principally aquatic species, most ponds are colonised through overland migration. The consequences of this finding for invasions in France and other European countries are briefly discussed.