Rapid poleward distributional shifts in the European cave-dwelling Meta spiders under the influence of competition dynamics

Aim: To describe the distribution of two congeneric species of cave-dwelling spiders under current climatic conditions and future warming scenarios, keeping into account their bioclimatic requirements, dispersal capacity and competition dynamics. Location: Europe and North Africa. Methods: We gathered detailed occurrence data for Meta menardi and M. bourneti (Araneae: Tetragnathidae) and modelled their distribution across their bioclimatic range. We evaluated the breadth of the bioclimatic niche of the two species and assessed the potential overlap between their multidimensional Hutchinsonian hypervolumes. We compared these results with their current distribution maps obtained by species distribution modelling (SDMs) keeping into account dispersal and competition dynamics, and we projected future trends of distribution according to different climatic scenarios. Results: The overall size of the niche hypervolumes of the two species was very similar and highly overlapping. However, when accounting for competition in the model, the predicted ranges of the two species showed only minor areas of overlap. On the base of SDM analysis, we predicted a significant poleward shift in the distribution of both species, with the appearance of a new contact area especially in Central Europe, southern UK, France and northern Spain. Main conclusions: Interspecific competition keeps the current ranges of the two European Meta species apart, although their fundamental bioclimatic niches are very similar. Rapid poleward shifts of the two species are likely due to the high dispersal capacity of the two spiders. The case of Meta spiders exemplifies rapid shift in range of distribution associated with global warming, which are unlikely to occur in the case of most cave-dwelling arthropods