Sign in

Defining the appropriate spatial scale for robust estimates of risks to species and ecosystems

IUCN scientists demonstrate that estimates of the Area of Occupancy (AOO) at scales proportional to the spatial extent of the threats are robust predictors of risks to biodiversity.

Facing environmental degradation is a great global challenge. It causes the loss of biodiversity as well as of ecosystem services and functions, which can result in the extinction of species and the collapse of ecosystems. Therefore, the International Union for the Conservation of Nature (IUCN) has developed the Red Lists in order to assess the risks to biodiversity at different scales by applying criteria that are consistent, transparent, scientifically rigorous and easy to understand.

The spatial distribution and the area of occupancy (AOO) are key indicators to predict biodiversity risk at multiple levels of biological organization, and as such are included in red list assessments. Despite the relevance of these predictors, for a long time, there has been a controversy regarding the appropriate spatial scales at which they must be estimated to assess the risks to species and ecosystems. In particular, the proper way to calculate the AOO for risk assessments using a grid with cells of standard dimensions has been much debated.


To address this situation, scientists from the IUCN Red List of Ecosystems thematic group carried out the first comprehensive assessment of scale-sensitivity in AOO as a predictor of risks to biodiversity. Their results, presented in the article "Scaling range sizes to threats for robust predictions of risks to biodiversity", indicate that AOO is a strong predictor of risks to biodiversity at relatively coarse scales, commensurate with the spatial extent of events that threatened the persistence of species and ecosystems. In this work, a model was used to simulate a landscape with different distribution patterns, with the aim of representing the range of variation in the spatial occupation of species and ecosystems commonly found in nature. As part of the methods, the scale-area relationships were characterized and the AOO was calculated for each type of distribution using different cell sizes. Finally, the footprints of threat regimes with different frequencies and extent were simulated and the risk of extinction or collapse for each type of distribution and threat regime was estimated. The performance of the AOO as a risk predictor was best when the cell sizes were between 0.1 and 1.0 times the spatial extent of the threats.

The results confirmed the relevance of AOO as an indicator in biodiversity risk assessments. In addition, it was described for the first time how the performance of AOO varies with the spatial scale in which it is estimated, the geometric uncertainty and the spatial characteristics of the threat regimes. On the other hand, the results indicate that the current IUCN guidelines for the estimation of AOO incorporate effective procedures for the assessment of the risks to species and ecosystems presented by threats at the landscape scale. Consistent application of these methods underpins the reliability of meta-analyses that provide essential information for the development and implementation of conservation policies.



Written by: Mariana C. Hernández-Montilla

Style and Format: Lila García and Irene Zager

Translation: Irene Zager


Provita May 17, 2018


IUCN Red List of Ecosystems


Subscribe to our newsletter!