Jp. Pointier et al., Introduction and spread of Thiara granifera (Lamarck, 1822) in Martinique,French West Indies, BIODIVERS C, 7(10), 1998, pp. 1277-1290
We followed the invasion dynamics of the Oriental thiarid snail Thiara gran
ifera on the Martinique island, French Antilles. This freshwater species wa
s first discovered in 1991 in the Charpentier River, and its spread has sin
ce been analysed based on a yearly survey of the malacological fauna at mor
e than 100 sites covering the whole island and representing 50 river system
s and three pools. Four river systems were sampled at many sites. Thirteen
river systems were colonized by 1997. Colonization within river systems occ
urred at a speed greater than 1 km per year, probably resulting from both a
ctive and passive dispersal. Our results can, on the whole, be explained by
a simple diffusion process, However, stratified diffusion has to be invoke
d in at least one river. Moreover, colonization was faster downstream than
upstream, suggesting that current velocity plays a significant role in disp
ersal. Dispersal also occurred between river systems at a mean distance of
almost 10 km, though with a large variance, in accordance with the scattere
d colony model of stratified diffusion. The relative frequencies of T. gran
ifera and Melanoides tuberculata, another recent invader of Martinique, wer
e followed at three sites on the Lezarde River. The first species quickly o
utnumbered the second, though never wiped it out. The data therefore do not
support any exclusion phenomena between these two parthenogenetic invaders
. Our analysis does not indicate any obvious influence of the rise of T. gr
anifera on the local freshwater fauna.