Modelling the geographical distributions of one native and two introduced species of crayfish in the French Alps

The French Alps is an important area for several species of crayfish; some species are native in this region and several were introduced by humans. The present study aimed at modelling the distributions of these two cate­ gories of species and find the significant environmental variables to explain these distributions. Field sampling was performed in this region in 2014 resulting in enough data for modelling the distribution of three species, one native (the white-clawed crayfish, Austropotamobius pallipes) and two introduced from North America (the spiny-cheek crayfish, Faxonius limosus, and the signal crayfish, Pacifastacus leniusculus). Environmental data were collected from different sources and included altitude, slope, land cover, and several water quality measures such as nitrate and ammonium concentrations. The two introduced species showed different influential variables compared to the white-clawed crayfish. Currently, it is unlikely that the two introduced species affect negatively the native white-clawed crayfish. The most important threat for this species seems to be the increase of tem­ perature caused by global warming. If the introduced species continue to spread, they may provide a synergy with the increase of temperature and threaten the native populations. It appears crucial to continue the moni­ toring of these species in this area. Future investigations should be carried out to understand the relationships between present crayfish spatial distribution and pathogens carried by alien species as these might be critical factors mediating the interactions among these species.