Extinction Rates and Trends

8 IUCN

The IUCN Red List of threatened species. Version 2018-2. To assess general trends and dynamics of processes underlying recent plant extinctions, we expanded upon the International Union for Conservation of Nature’s (IUCN) current list of 153 global vascular plant extinctions [], using data from regional and country-specific Red Lists, Red Data Books, and expert surveys, covering floras from both biodiversity hot- and coldspots ( Tables S1 and S2 Figure S1 ). Our data included floras from ten hotspots (California Floristic Province, Cape Floristic Region, Chilean Winter Rainfall and Valdivian Forests, Mediterranean Basin, Maputuland-Pondoland-Albany, New Zealand, Easter Island as part of Polynesia-Micronesia, Southwest Australian Floristic Region, Succulent Karoo, Sri Lanka as part of the Western Ghats, and Sri Lanka hotspot) and six coldspots (Chile—excluding areas that politically belong to the country but are declared biodiversity hotspots, England, Germany, Russia, Ukraine, and Uzbekistan). In total, these regions represent around 15.3% of the globe’s land surface ( Figure S1 ). Both global (i.e., EX/EW) and regional (RE sensu IUCN) extinctions were included. The latter was only included when they led to the extinction of a particular species from a biodiversity hot- or coldspot region considered here. In three instances, extinction of the same species was documented in two coldspot regions: Crassula aquatica and Najas flexilis (England and Germany) and Subularia aquatica (Germany and Ukraine). Despite obvious shortcomings, we argue that regional extinctions still provide valuable data to make general inferences around plant extinctions and that the drivers underlying these extinctions are likely representative of those faced by plants across their distributional ranges.

9 Humphreys A.M.

Govaerts R.

Ficinski S.Z.

Lughadha E.N.

Vorontsova M.S. Global Dataset Shows Geography and Life Form Predict Modern Plant Extinction and Rediscovery. 10 Hulme P.E. Trade, transport and trouble: managing invasive species pathways in an era of globalization. 11 Turner B.L.

Clark W.C.

Kates R.W.

Richards J.F.

Mathews J.T.

Meyer W.B. The Earth as Transformed by Human Action: Global and Regional Changes in the Biosphere over the Past 300 Years. 12 Bulliet R.W.

Crossley P.K.

Headrick D.R.

Hirsch S.W.

Johnson L.L.

Northrup D. The Earth and Its Peoples – A Global History. ∗year + c(HS versus CS) + d∗year∗c(HS versus CS)]; Efron’s Pseudo R2 = 0.868; b = 0.0139 ± 0.0002, Z = 61.2143, p < 0.0001), but faster for hotspots (c = 1.6743 ± 0.1265, Z = 13.2391, p < 0.0001) with the rising rate occurring later in coldspots than in hotspots (d = 0.0031 ± 0.0005, Z = 6.5932, p < 0.0001). Indeed, we expected biodiversity hotspots to have disproportionally higher numbers and faster rates of plant extinction events compared to coldspots due to their high levels of endemism and diversity, usually confined to small and unique geographic areas [ 13 Brooks T.M.

Mittermeier R.A.

Mittermeier C.G.

Fonseca G.A.B.

Rylands A.B.

Konstant W.R.

Flick P.

Pilgrim J.

Oldfield S.

Magin G.

et al. Habitat loss and extinction in the hotspots of biodiversity. 14 Darrah S.E.

Bland L.M.

Bachman S.P.

Clubbe C.P.

Trias-Blasi A. Using coarse-scale species distribution data to predict extinction risk in plants. Figure 1 Plant Extinctions over the Last 300 Years for Biodiversity Hotspots (Red Lines, n = 157), Coldspots (Blue Lines; n = 107), and Hot- and Coldspots Combined (Black Lines; n = 264) Show full caption (A) Cumulative number of documented extinction events since 1700. Gray dots indicate recorded extinction events and curve-fitted polynomial GLM-Poisson regressions from our modeling approach (see Supplemental Information for details). The cumulative proportion of lost hotspot and coldspot plant diversity is indicated by red and blue shaded area graphs, respectively, in the background. (B) Annual extinction rate (i.e., number of extinctions per year). (C) Annual extinction rate presented in a logarithmic scale for comparison with the background extinction rates calculated for biodiversity hotspots (dashed red line: calculation based on number of all plant species in the corresponding hotspots) and coldspots (dashed blue line: calculation based on number of all plant species in the corresponding coldspots; see Supplemental Information for details). Please note that these graphs only include extinction events for which the date of extinction is known (for 27 extinctions, these data were unavailable). Asterisks in Figure 1 A indicate the total number of extinctions when including these extinction events lacking dates (18 for hotspots and 9 for coldspots). Please see also Figure S1 and Tables S1 and S2 While a recent study documented more than 500 globally extinct plant species [], our dataset is remarkable in that for most of the 291 extinctions we identified, we were able to obtain information on: the number of years since extinction (n = 264), reason(s) for extinction (11 non-exclusive categories, together with a category for multiple reasons as well as unknown reasons; Figures 2 and 3 Tables S1 and S3 ), a measure of lost taxonomic uniqueness (i.e., proportion of genus lost per extinction event), and life-form (see STAR Methods ). Our data show that extinction rates for both hotspots and coldspots accelerated since the Industrial Revolution ( Figure 1 B). The Industrial Revolution resulted in rapid increases in human population sizes and densities, in part due to higher longevity as afforded by better living conditions, especially in Eurasia and North America. This period also coincided with an increased need for raw materials for construction and manufacturing, leading to high levels of habitat destruction through infrastructure development, the introduction of exotic species [], and the rapid expansion of forestry and agricultural areas []. Cumulative extinctions (CumExt) accelerated for both hotspots (HS) and coldspots (CS) from 1750 to present ( Figure 1 A) (GLM: CumExt ∼Exp[a + byear + c(HS versus CS) + dyearc(HS versus CS)]; Efron’s Pseudo R= 0.868; b = 0.0139 ± 0.0002, Z = 61.2143, p < 0.0001), but faster for hotspots (c = 1.6743 ± 0.1265, Z = 13.2391, p < 0.0001) with the rising rate occurring later in coldspots than in hotspots (d = 0.0031 ± 0.0005, Z = 6.5932, p < 0.0001). Indeed, we expected biodiversity hotspots to have disproportionally higher numbers and faster rates of plant extinction events compared to coldspots due to their high levels of endemism and diversity, usually confined to small and unique geographic areas []. Plant extinctions peaked half a century later in coldspots than in hotspots (1974 versus 1921) ( Figure 1 B), likely as a result of lower levels of endemism in these areas, which, in turn, are usually linked to wider geographic distributions and therefore generally less susceptibility to extinction []. As the 114 RE events predominantly occurred in coldspots (76.3%), removing these records led to a rather similar estimate of the extinction rate in hotspots (peaking at 1.47 E/Y in 1921) and a continuously rising, but much lower, extinction rate in coldspots (< 0.2 E/Y).

3 Pimm S.L.

Jenkins C.N.

Abell R.

Brooks T.M.

Gittleman J.L.

Joppa L.N.

Raven P.H.

Roberts C.M.

Sexton J.O. The biodiversity of species and their rates of extinction, distribution, and protection. 15 Vellend M.

Baeten L.

Becker-Scarpitta A.

Boucher-Lalonde V.

McCune J.L.

Messier J.

Myers-Smith I.H.

Sax D.F. Plant biodiversity change across scales during the Anthropocene. 16 Gray A. The ecology of plant extinction: rates, traits and island comparisons. th order GLM fitted cumulative rate of extinction). These rates correspond well with another recent estimate for global plant extinctions [ 9 Humphreys A.M.

Govaerts R.

Ficinski S.Z.

Lughadha E.N.

Vorontsova M.S. Global Dataset Shows Geography and Life Form Predict Modern Plant Extinction and Rediscovery. 17 Pimm S.L.

Joppa L.N. How many plant species are there, where are they, and at what rate are they going extinct?. Current estimates of background extinction rates (BERs: typical rates of extinction during the planet’s geological and biological history, prior to human influence) vary around 0.1 (between 0.05 to 0.15) extinctions per million species years (E/MSY) [] and would, for the biodiversity hotspots included here, translate to 0.00701 E/Y ( Figure 1 C; Table S2 STAR Methods ). For biodiversity hotspots, we estimated the extinction rate to be 0.036 E/Y in 1750, or 5.1 times that of the estimated hotspot BER, jumping to 0.321 E/Y or 45.8 times the BER in 1850. In 1921, the extinction rate for biodiversity hotspots reached its peak: 1.65 E/Y or 235.4 times the BER (i.e., 23.5 E/MSY) and declined in the 1970’s from 0.540 to 0.437 E/Y or from 77.0 to 62.3 times the BER (extinction rates calculated as the derivative of the 7order GLM fitted cumulative rate of extinction). These rates correspond well with another recent estimate for global plant extinctions [] and are still at least one order of magnitude lower than previous estimates of between 1,000 to 10,000 times the BER (e.g., []). For the biodiversity coldspots considered in this study, a BER of 0.1 would translate to 0.00279 E/Y, which is 2.4 times lower than that for hotspots ( Figure 1 C; Data S1 STAR Methods ). In 1921, when the extinction rate peaked in hotspots, the extinction rate for coldspots was 0.636 E/Y or 228 times the BER (i.e., 22.8 E/MSY), and it reached its maximum in 1974 with an estimated rate of 0.987 E/Y or 353.8 times the BER (i.e., 35.4 E/MSY, Figure 1 C). After 1974, extinction rates for biodiversity coldspots decelerated to around 0.670 E/Y or 240 times the BER ( Figure 1 ).