1. Species absent from a community, but with the potential to establish (dark diversity) are an important, yet rarely considered, component of habitat specific species pools. However, quantifying this component remains a challenge as dark diversity cannot be observed directly, and must be estimated. Here, we empirically test whether species ecological requirements or species co-occurrences provide accurate estimates of dark diversity. 2. We used two spatially nested independent datasets, one comprising 3033 samples of coastal...