Essays and perspectives
Global endemics-area relationships of vascular plants

https://doi.org/10.1016/j.pecon.2019.04.002Get rights and content
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Highlights

  • Endemics–area relationships (EARs) are largely lacking for plants.

  • Our new EAR method overcomes key biases to model expected numbers of plant endemics.

  • Our global model for vascular plants is Endemics = 0.00001227·Area1.195 (area in km2).

  • The model gives baseline endemism for circular areas in the range 104–108 km2 E = 0.0000127·A1.195.

  • The average area needed for at least one endemic vascular plant species as 12,875 km2.

Abstract

Endemics–Area Relationships (EARs) are fundamental in theoretical and applied biogeography for understanding distribution patterns and promoting biodiversity conservation. However, calculating EARs for vascular plant species from existing data is problematic because of biased knowledge of endemic species distributions and differences between taxonomies. We aimed to overcome these challenges by developing a new standardized global dataset based on expert knowledge to produce a set of global EARs.

We developed a nested circle design, with grain sizes of 104, 105, 106, 107, and 108 km2, respectively, and a global distribution of plots based on a stratified random scheme. The number of vascular plant species endemic to each circle was then estimated independently by five experts randomly chosen from a pool of 23, as both a minimum and a maximum value (lower and upper bounds of the estimation), taking into account the limitations of current knowledge and varied species concepts in existing taxonomies. This procedure resulted in a dataset of 3000 expert estimates.

Based on the data, we produced three global EARs for endemic species richness using minimum, maximum and average estimates. As a validation, we used all three models to extrapolate to the entire world, producing estimates of 284,493 (minimum), 398,364 (maximum) and 312,243 (average) vascular plant species. These figures conform to the range of taxonomists’ estimates. From the models, we calculated the average area needed to harbour a single endemic species as 12,875 km2 (range 9675–20,529).

The global vascular plant EARs we calculated represent the first standardized, quantitative expectations of plant endemism at any given scale (sampling unit size). These EARs allow us to provide a clear answer to a long-standing but elusive biogeographical question: how to assess whether any area on the surface of the Earth is rich or poor in endemics relative to the average.

Keywords

Expert knowledge
Minimum and maximum estimates
Zero-endemic plots
Distribution of land and sea
Global reference

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