Narrowly distributed taxa are disproportionately informative for conservation planning.

Biological atlas data can be used as inputs into conservation decision-making, yet atlases are sometimes infrequently updated, which can be problematic when the distribution of species is changing rapidly. Despite this, we have a poor understanding of strategies for efficiently updating biological atlas data. Using atlases of the distributions of 1630 threatened plant taxa, we quantitatively compared the informativeness of narrowly distributed and widespread taxa in identifying areas that meet taxon-specific conservation targets, and also measured the cost-efficiency of meeting those targets. We also explored the underlying mechanisms of the informativeness of narrowly distributed taxa. Overall, narrowly distributed taxa are far more informative than widespread taxa for identifying areas that efficiently meet conservation targets, while their informativeness for identifying cost-efficient areas varied depending on the type of conservation target. Narrowly distributed taxa are informative mainly because their distributions disproportionately capture areas that are either relatively taxon rich or taxon poor, and because of larger number of taxa captured with given number of records. Where resources for updating biological data are limited, a focus on areas supporting many narrowly distributed taxa could benefit conservation planning.