Abstract
Accurate extent of occurrence (EOO) estimates are essential for reliable conservation assessments. Recent studies suggest that current EOO maps often significantly overestimate range sizes of birds, particularly for narrow-ranging, threatened and ecological specialist species. Such species may therefore be at danger of being falsely overlooked by conservation assessments. Using species distribution modeling combined with ‘expert’ review and according corrections of inductive models, we estimated historic range sizes of 15 Bolivian endemics, which were compared to BirdLife International’s 2011 EOO estimates. The same comparisons were made for 65 additional species modeled by Young et al. (Auk 126:554–565, 2009) to corroborate the general validity of our results. Species distributions were modeled deductively for eight, with a hybrid approach for six and inductively for one species. For 67 % of Bolivian endemics, EOO estimates were 1.48–4.22 times larger than our estimates (1.75–4.33 larger for 89 % of the species in Young et al.). Overestimation can largely be attributed to inclusion of areas outside a species’ elevational range and of portions of ecoregions or extensive habitat areas uninhabited by a species. For 33 % of Bolivian endemics (all threatened species), EOO estimates were 21.2–75.3 % smaller than our estimates (30.3–72.2 % smaller for 11 % of the species in Young et al.). This can partly be attributed to more sophisticated range size analyses for threatened species by BirdLife, differences between historic versus current range sizes, and overly conservative EOO estimates. EOO definition and estimates are in serious need of improvement. Exclusion of discontinuities within overall distributions of species needs to be applied rigorously at small spatial scales, using spatially explicit environmental data such as digital elevation models and ecosystem classifications. Incorporating national expert knowledge into range size estimation can be similarly important for reducing overestimation. We recommend prioritizing species with EOO estimates of <200,000 km2 for a revision of these estimates.
Zusammenfassung
Arealgrößenschätzungen endemischer Vögel Boliviens neu betrachtet: die Bedeutung von Umweltparametern und nationalem Expertenwissen
Akkurate Schätzungen der Größe von Verbreitungsarealen (extent of occurrence, EOO) sind essenziell für eine verlässliche Bewertung des Gefährdungsgrades von Arten. Neueste Studien zeigen, dass derzeitige EOO-Karten die Verbreitungsareale von Vogelarten oft signifikant überschätzen, besonders für geographisch eng verbreitete, bedrohte und ökologisch spezialisierte Arten. Solche Arten laufen daher Gefahr, bei Gefährdungsbewertungen fälschlicherweise übersehen zu werden. Mittels Verbreitungsareal-Modellierung kombiniert mit Experteneinschätzung und entsprechender Korrektur induktiver Modelle schätzten wir die historischen Arealgrößen von 15 bolivianischen Endemiten. Diese Werte wurden mit den EOO-Schätzungen von BirdLife International aus dem Jahr 2011 verglichen. Um die generelle Gültigkeit unserer Ergebnisse zu überprüfen, stellten wir denselben Vergleich mit 65 zusätzlichen Arten an, deren Areale von Young et al. (Auk 126:554–565, 2009) modelliert wurden. Artenareale wurden deduktiv modelliert für acht Arten, mit einem Hybridansatz für sechs Arten und induktiv für eine Art. Für 67 % der bolivianischen Endemiten waren EOO-Schätzungen 1,48–4,22 Mal größer als unsere Schätzungen (1,75–4,33 Mal größer für 89 % der Arten aus Young et al.). Diese Überschätzung kann größtenteils zurückgeführt werden auf die Einbegreifung von Gebieten außerhalb der Höhenverbreitung einer Art und von Teilen von Ökoregionen oder ausgedehnter Habitatareale, die von der jeweiligen Art nicht bewohnt werden. Für 33 % der bolivianischen Endemiten (allesamt bedrohte Arten) waren EOO-Schätzungen 21,2–75,3 % kleiner als unsere Schätzungen (30,3–72,2 % kleiner für 11 % der Arten aus Young et al.). Dies liegt zum Teil an der differenzierteren Bestimmung von Verbreitungsarealen für bedrohte Arten durch BirdLife, an Unterschieden zwischen historischen und heutigen Arealgrößen sowie übermäßig konservativen EOO-Schätzungen. Sowohl die Definition von EEOs als auch EOO-Schätzungen sind verbesserungswürdig. Der Ausschluss von durch eine Art nicht bewohnten Gebieten innerhalb ihres gesamten Verbreitungsareals sollte rigoros auf kleinen räumlichen Skalen angewandt werden, unter Einbeziehung räumlich expliziter Umweltdaten wir z.B. digitaler Höhenmodelle und Ökosystemklassifikationen. Die Einbeziehung nationalen Expertenwissens in die Schätzung von Arealgrößen kann ähnlich wichtig für eine Verringerung von Überschätzungen sein. Wir empfehlen, Arten mit EOO-Schätzungen von <200,000 km2 für eine Überprüfung dieser Werte zu bevorzugen.
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Acknowledgments
We thank the numerous individuals, institutions and organizations that contributed their unpublished data to Armonía’s distributional bird database. This study was made possible by funds from the John D. and Catherine T. MacArthur Foundation (Grant 08-91570-000, GSS) and the Netherlands Embassy to Fundación Amigos de la Naturaleza. Previous support for Armonía’s distributional bird data base was provided by The Nature Conservancy, NatureServe and WWF Bolivia. We thank D.M. Larrea-Alcázar for helpful discussions and comments on the manuscript. Two anonymous reviewers also made helpful comments on the manuscript.
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Herzog, S.K., Maillard Z., O., Embert, D. et al. Range size estimates of Bolivian endemic bird species revisited: the importance of environmental data and national expert knowledge. J Ornithol 153, 1189–1202 (2012). https://doi.org/10.1007/s10336-012-0850-2
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DOI: https://doi.org/10.1007/s10336-012-0850-2