You may have seen coverage of a recent paper in Nature in which Kew researchers quantified the rate of plant extinction over the last 250 or so years. The headline number is about 3 species have been going extinct per year, which is about 500 times the background rate. But I know that what you really want to know is how many of these are crop wild relatives. Well, my friends at CIAT worked their database magic, and came up with the following list of extinct species which are classified by at least one source as a crop wild relative:
Diplotaxis siettiana
Franklinia alatamaha
Helianthus praetermissus
Hutchinsia tasmanica
Ilex gardneriana
Isatis arnoldiana
Lepidium drummondii
Lepidium obtusatum
Mangifera casturi
Musa fitzalanii
Piper collinum
Potentilla multijuga
Rorippa coloradensis
Solanum bauerianum
Solanum cajamarquense
Solanum ruvu
Syzygium balfourii
Syzygium microphyllum
Syzygium palghatense
Which means about 1 per decade or thereabouts. But that, clearly, is just a minimum.
Perhaps I’ll try to map where these plants were last seen.
Extinct wild relatives
As a botanist since I was knee high I simply can’t believe the extinction rate of three species lost a year is 500 times the natural background rate. One example from the list, Isatis arnoldiana (Arnoldi’s woad), is only known from the type collection – an uncertain locality in Armenia. The IUCN Red List has it as `data deficient’: it could still be there or in other localities. Also the natural loss of species could have been immense. Any climatic warming and cooling, Ice Ages for example, will force small populations on peninsulas or mountains to move and `fall off the edge’. We are talking of thousands of species being lost as recently as the climatic cooling – and subsequent rapid warming – of the Younger Dryas. The rate of description of new plant species is about 2000 a year. What is the fuss about?
Back of the envelope calculations…
The recurrence time of ice ages is about 100,000 years. If ice ages have more impact than humans, each ice age would need to make more than 3 species / year * 100,000 years = 300,000 species go extinct. We have about 391,000 vascular plant species right now, and we just come out of an ice age. So the extinction rate of ice ages is only lower than 3 species / year if the last ice age wiped out around half of the plant diversity that existed before it. That seems unlikely to me. So there is reason to make fuss.
For crop wild relatives, we would have an extinction rate of about 0.1 species per year, Luigi writes. It would be interesting to know if the CWR extinction rate is higher or lower than the average one. The absolute extinction rate for CWRS is 3 / 0.1 = 30 times lower than for all plants. If less than 1/30 of all plants is a CWR, the extinction rate of CWR is higher than the average plant extinction rate. In other words, if there are less than 391,000/30= 13,033 CWR species. That seems like a lot to me, so I would guess that CWR have an even higher extinction rate than 500 times the background rate. How many CWR are there on the list of your friends, Luigi?
Not many of my friends are CWR, as far as I know.
You make lists of friends?
Constantly.
Is it from the list of 1076 taxa (Castañeda-Alvarez et al. 2016)? That would mean that the extinction rate of CWR is much higher than that of all vascular plants.