Accelerating the monitoring of global biodiversity: Revisiting the sampled approach to generating Red List Indices

Sérgio Henriques,Craig Hilton‐Taylor,Jennifer Luedtke,Robin Freeman,Ben Collen,Stuart H M Butchart,Michael Hoffmann,Monika Böhm,Pedro Cardoso

doi:10.1111/conl.12703

Abstract

AbstractGiven the current biodiversity crisis, pragmatic approaches to detect global conservation trends across a broad range of taxa are critical. A sampled approach to the Red List Index (RLI) was proposed, as many groups are highly speciose. However, a decade after its conception, the recommended 900 species sample has only been implemented in six groups and trend data are available for none, potentially because this sample is unfeasibly high.Using a broader set of all available data we show that when re‐assessments are conducted every 10 years, 200 species (400 in some cases) should be sufficient to detect a RLI trend. Correctly detecting changes in slope still requires samples of 900 species (11,000 in some cases).Sampled assessments can accelerate biodiversity monitoring and complement current metrics, but the time‐period between assessments and the approaches’ purpose should be carefully considered, as there is a trade‐off between sample size and the resulting indices.

Highlights

The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is the world’s most comprehensive repository of conservation assessments, containing information on the extinction risk of more than 105,000 species (IUCN, 2019)
The minimum sample size that correctly represented the Red List Index (RLI) trend direction in at least 95% of the simulated samples was ≤200 species for corals (10-year interassessment period), cycads (11 years), mammals (12 years), and amphibians (24 years) (Figures 1A–D), ≤400 species for two of the interassessment periods for birds but 2700 were needed as a minimum sample for the group overall (Figures 1E–J)
When measuring the effect of interassessment length, we found that for periods of ten years or longer, the minimum sample size required to correctly detect trend direction in all species groups was 400 non-DD species, 200 nonDD species sufficed for all nonavian taxa (Figure 3)

Summary

Introduction

The International Union for Conservation of Nature (IUCN) Red List of Threatened Species (hereafter Red List) is the world’s most comprehensive repository of conservation assessments, containing information on the extinction risk of more than 105,000 species (IUCN, 2019). This only encompasses 5% of the world’s 1.8 million recorded species, and less than 1% of Earth’s estimated biodiversity (Mora, Tittensor, Adl, Simpson, & Worm, 2011). We lack a holistic understanding of extinction risk at a global scale, and the estimate that 1 million species face extinction.

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Conclusion