Estimating dark diversity and species pools: an empirical assessment of two methods

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 grassland vegetation plots of 4m2 and 200m2 from Scotland, UK and another comprising 780 samples of forest vegetation plots of 30m2 and 500m2 from Switzerland. Dark diversity for each of the smaller scaled plots was estimated through investigating the degree of 1) similarity in ecological requirements (measured as Ellenberg values) and 2) co-occurrence likelihood of all species observed. Estimates were validated through comparing estimates with observed species at ...