ConclusionsBased on one simulated and two empirical examples we demonstrate that probabilistic species pools allow us to disentangle the geographical variation in dispersal, environmental and biotic assembly processes for species assemblages in focal units. We also show that probabilistic species pools are fully compatible with traditional definitions of species pools and are applicable over a wide range of spatial and temporal extents. Additionally they are robust to missing data and provide a quantified and transparent approach to estimating the size and composition of species pools in a mechanistic way, providing a valuable tool for studies from community ecology to macroecology.