Why are some species common while others are rare?

Massive study of global distributions show that more than a third of Earth's plants are exceedingly rare

Data resources used via GBIF : 215,046,618 species occurrences
Aloidendron dichotomum
Quiver tree (Aloidendron dichotomum) observed near Warmbad, Namibia by Conor Eastment. Photo via iNaturalist (CC BY-NC 4.0

The phenomenon that some species are very common while others incredible 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 BIEN global plant database, which draws on GBIF as main source of occurrences, to perform an unpresedented 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—that rapid changes in temperature negatively affects retention of rare species.

Original article

Enquist BJ, Feng X, Boyle B, Maitner B, Newman EA, Jørgensen PM, Roehrdanz PR, Thiers BM, Burger JR, Corlett RT, Couvreur TLP, Dauby G, Donoghue JC, Foden W, Lovett JC, Marquet PA, Merow C, Midgley G, Morueta-Holme N, Neves DM, Oliveira-Filho AT, Kraft NJB, Park DS, Peet RK, Pillet M, Serra-Diaz JM, Sandel B, Schildhauer M, Šímová I, Violle C, Wieringa JJ, Wiser SK, Hannah L, Svenning J-C and McGill BJ (2019) The commonness of rarity: Global and future distribution of rarity across land plants. Science Advances. American Association for the Advancement of Science (AAAS) 5(11): eaaz0414. Available at: https://doi.org/10.1126/sciadv.aaz0414