Distribution and ecological preferences of noble crayfish in the Carpathian Danube basin: biogeographical insights into the species history

Widespread across Europe, the noble crayfish Astacus astacus has experienced many negative ecological and anthropogenic influences, mostly in western and northern Europe. We address the distribution and ecological affinities of this species in the geographical context of the Carpathian Danube basin, an area where these influences were limited and the distribution picture is expectedly a natural one. The main statistical method used to reveal the environmental factors that influence the distribution of noble crayfish was boosted regression trees. Crayfish presence was found to be favoured by a combination of a high percentage of riverbank tree coverage, moderate altitude and slow water velocity, to the detriment of dissolved oxygen. These results reveal the species requirements for river sectors offering the best long-term stability. An eastwards decrease in the probability of occurrence of noble crayfish populations was observed along the Danube tributaries. We hypothesise that this pattern is given by the early colonisation routes originating from southern Danube tributaries, after the Pleistocene glaciations. Including spatiality along with ecological data in the statistical models, this study comes to support the fact that a comprehensive approach can provide a better understanding of a species distribution pattern.