The phenomenon that some species are very common while others incredibly rare has always puzzled ecologists. Studies have investigated this on a local scale, but as most species are common in some parts of their ranges while rare in others, results are usually poor estimates of true global rarity.
This paper uses the Botanical Information and Ecology Network (BIEN) global plant database, which draws on GBIF as the main source of occurrences, to perform an unprecedented assessment of global patterns of rarity. By quantifying the global species abundance distribution (gSAD)—a functional measure of true abundance—of 435,000 species, the authors showed that 36.5 per cent are rare, with just five records or fewer.
While distributed globally, very rare species are more common in hotspots found in Central and South America, southern Africa and Madagascar, and across Asia-Pacific from China to New Guinea.
When exploring drivers of rarity, models showed that the most important predictor of plant rarity is a stable climate, and that rapid changes in temperature negatively affects retention of rare species.