A simple method for assessing the completeness of a geographic range size estimate

Garima Gupta,Jonathon Dunn,Roy Sanderson,Richard Fuller,P.J.K Mcgowan

doi:10.1016/j.gecco.2019.e00788

Garima Gupta, Jonathon Dunn + Show 3 more

Open Access

https://doi.org/10.1016/j.gecco.2019.e00788

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Abstract

Measuring geographic range size is a fundamental part of ecology and conservation. Geographic range size is used as a criterion by the IUCN Red List of Threatened Species in estimating species extinction risk. Yet the geographic distributions of many threatened species are poorly documented, and it is often unclear whether a geographic range size estimate is complete. Here we use a large and near-exhaustive database of species occurrences to (i) estimate extent of occurrence (a measure of geographic range size routinely used in Red List assessments), and (ii) develop a method to assess whether our estimate for each species is complete. We use an extensive database of point locality records for 24 Himalayan Galliformes, a group of highly threatened bird species. We examine the chronological pattern of increase of geographic range size estimates and compare this accumulation curve with a null model generated by performing 1000 iterations for each species using the point locality information in random order. Using Generalised Estimation Equations (GEE) and Generalised Least Square (GLS), we show that estimates of geographic range size for most species has now asymptoted, and that the range size estimates have improved more rapidly over time than expected by chance, suggesting relatively efficient sampling over time. The approach used in this study can be used as a simple method for assessing the completeness of a geographic range size estimates for any taxon.

Highlights

The geographic distribution of a species is fundamental to understanding its ecology and conservation needs, and there has been much research analysing the spatial occurrence of biodiversity (Gaston, 2000; Myers et al, 2000; Hawkins et al, 2003; Koleff et al, 2003; Orme et al, 2005; Naidoo et al, 2008)
The random simulation models showed that sampling all areas of a geographic range with equal probability should lead to an asymptotic area accumulation curve, with the probability of each new record falling within the known minimum convex polygon (MCP) range increasing as each record is added
We found that our knowledge of the geographic range sizes of Himalayan Galliformes is generally rather complete, has improved rapidly over time, and has accelerated since 1970

Summary

Introduction

The geographic distribution of a species is fundamental to understanding its ecology and conservation needs, and there has been much research analysing the spatial occurrence of biodiversity (Gaston, 2000; Myers et al, 2000; Hawkins et al, 2003; Koleff et al, 2003; Orme et al, 2005; Naidoo et al, 2008). G. Gupta et al / Global Ecology and Conservation 21 (2020) e00788 imminent extinction, because species with small geographic range are more vulnerable to stochastic threats than species with widespread distributions, and declining geographic range can lead to population reductions (Bland et al, 2016). It allows us to understand global patterns of biodiversity in relation to threats (Joppa et al, 2016), which enables conservationists to identify how best to ameliorate threats and to target conservation actions. The distributions of species are commonly used to evaluate the coverage of protected areas, and to inform the placement of new protected areas (Venter et al, 2014; Watson et al, 2014; Butchart et al, 2015)

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