Abstract

Area of Habitat (AOH) is a deductive model which maps the distribution of suitable habitat at suitable altitudes for a species inside its broad geographical range. AOH maps have been validated using presence-only data for small subsets of species for different taxonomic groups, but no standard validation method exists when absence data are not available. We develop a novel two-step validation protocol for AOH which includes first a model-based evaluation of model prevalence (i.e, the proportion of suitable habitat within a species’ range), and second a validation using species point localities (presence-only) data. We applied the protocol to AOH maps of terrestrial birds and mammals. In the first step we built logistic regression models to predict expected model prevalence (the proportion of the range retained as AOH) as a function of each species’ elevation range, mid-point of elevation range, number of habitats, realm and, for birds, seasonality. AOH maps with large difference between observed and predicted model prevalence were identified as outliers and used to identify a number of sources of systematic error which were then corrected when possible. For the corrected AOH, only 1.7 % of AOH maps for birds and 2.3 % of AOH maps for mammals were flagged as outliers in terms of the difference between their observed and predicted model prevalence. In the second step we calculated point prevalence, the proportion of point localities of a species falling in pixels coded as suitable in the AOH map. We used 48,336,141 point localities for 4889 bird species and 107,061 point localities for 420 mammals. Where point prevalence exceeded model prevalence, the AOH was a better reflection of species’ distribution than random. We also found that 4689 out of 4889 (95.9 %) AOH maps for birds, and 399 out of 420 (95.0 %) AOH maps for mammals were better than random. Possible reasons for the poor performance of a small proportion of AOH maps are discussed.

Highlights

  • An accurate estimate of the distribution of species is central to ecological and conservation research and action

  • Geographic ranges, which are derived by mapping the extent of known point localities along with expert knowledge; and 3) species distribution models, which use environmental and other relevant variables associated with the species to refine geographical ranges

  • Habitat models are prone to two major types of errors: omission errors occur when suitable habitat areas for the species are wrongly mapped as being unsuitable, commission errors occur when areas unsuitable for the species are wrongly mapped as being suitable

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Summary

Introduction

An accurate estimate of the distribution of species is central to ecological and conservation research and action. There are three different classes of information on the distribution of species (Rondinini and Boitani, 2006). These are 1) point localities (latitude and longitude) of individuals; 2). Geographic ranges, which are derived by mapping the extent of known point localities along with expert knowledge; and 3) species distribution models, which use environmental and other relevant variables associated with the species to refine geographical ranges. Species distribution models are of two types (Stoms et al, 1992). The first are deductive models, which use expert-based information on species’ habitat use to model the suitable areas for the species. The second type are inductive models, in which the environmental conditions at point localities where the species were recorded are interpolated over wider areas

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