Have you ever wondered how many species were lost before we had the chance to discover them? In a paper now out in Conservation Biology, led by Nadiah, we estimated just that, for plant species in Singapore, following on from our lab’s related work on Singapore birds and butterflies.

All over the world, many species remain undiscovered while both known and unknown species continue to go extinct. This is particularly true in the tropics, where biodiversity is high and development continues apace. Singapore provides an invaluable case study of tropical biodiversity loss. Since British colonisation in 1819, most of Singapore’s forest cover has been replaced with urban landscape. However, Singapore also has one of the best-documented floras in the world, in terms of taxonomic and temporal coverage, with historical collections beginning only a few years after colonisation.

The orchid species Grammatophyllum speciosum has not been recorded in Singapore since 1918.
Photo credit: Cerlin Ng

We collated a high-quality database of over 30,000 Singapore plant collections representing over 2,000 species, and we applied our lab’s previously developed “SEUX” model to estimate extinction rates and total numbers over time. The SEUX model is based on a straightforward idea: if we assume that the per-year per-species extinction rates have been the same for discovered and undiscovered extinctions, then we have a basis for working backwards in time to estimate the number of undiscovered species and the proportion that went extinct. In the new paper we also developed a more accurate method for obtaining confidence intervals on the estimates.

We estimated that 30–38% of Singapore plant species have gone extinct since 1819. The central estimate using classical methods was 32% and that using Bayesian methods was 35%. Crucially, these numbers are much higher than the 22% extinction rate that one obtains from the naïve method of simply dividing the number of known extinctions by the total number of discovered species, demonstrating the importance of calculating extinction rates in a way that accounts for unknown species.

Also check out Nadiah’s blog post on the paper, her previous blog post giving a SEUX tutorial, and her SEUX for R package on GitHub. The full reference for the paper is below.

Kristensen, N. P., Seah, W. W., Chong, K. Y., Yeoh, Y. S., Fung, T., Berman, L. M., Tan, H. Z., Chisholm, R. A. (2020) Extinction rate of discovered and undiscovered plants in Singapore, Conservation Biology (in press)

From the Singapore plants database, we inferred the number of discovered species that were extant and extinct over time. We then used the SEUX model on these data to estimate the number of undiscovered species that were extant and extinct over time.