Contributed Paper Effects of Detectability on Estimates of Geographic Range Size in Bignonieae SEEMA NAYAN SHETH, * ‡L ´ UCIA G. LOHMANN, * † TRISHA CONSIGLIO, * AND IV ´ AN JIM ´ ENEZ * * Center for Conservation and Sustainable Development, Missouri Botanical Garden, P.O. Box 299, Saint Louis, MO 63166-0299, U.S.A. †Universidade de S˜ ao Paulo, Instituto de Biociˆ encias, Departamento de Botˆ anica, C.P. 11461, CEP 95422-970, S˜ ao Paulo, SP, Brazil Abstract: Extinction risk has not been evaluated for 96% of all described plant species. Given that the Global Strategy for Plant Conservation proposes preliminary conservation assessments of all described plant species by 2010, herbarium specimens (i.e., primary occurrence data) are increasingly being used to infer threat components from estimates of geographic range size. Nevertheless, estimates of range size based on herbarium data may be inaccurate due to collection bias associated with interspecific variation in detectability. We used data on 377 species of Bignonieae to test the hypothesis that there is a positive relationship between detectability and estimates of geographic range size derived from herbarium specimens. This relationship is expected if the proportion of the true geographic range size of a species that is documented by herbarium specimens is given by the product of the true geographic range size and the detectability of the species, assuming no relationship between true geographic range size and detectability. We developed 4 measures of detectability that can be estimated from herbarium data and examined the relationship between detectability and 2 types of estimates of geographic range size: area of occupancy and extent of occurrence. Our results from regressing estimates of extent of occurrence and area of occupancy on detectability across genera provided no support for this hypothesis. The same was true for regressions of estimated extent of occurrence on detectability across species within genera. Nevertheless, regressions of estimated area of occupancy on detectability across species within genera provided partial support for our hypothesis. We considered 3 possible explanations for this mixed outcome: violation of the assumption of no relationship between true geographic range size and detectability; the relationships between estimated geographic range size and detectability may be an artifact of a negative relationship between estimated area of occupancy and the sampling variance of detectability; detectability may have had 2 opposite effects on estimated species range sizes: one determines the proportion of the true range of a species documented by herbarium specimens and the other determines the distribution of true range size for the species actually observed with herbarium data. Our findings should help improve understanding of the potential biases incurred with the use of herbarium data. Keywords: area of occupancy, Bignoniaceae, Bignonieae, collection bias, extent of occurrence, geographic range size, herbarium specimens, species detectability Efectos de la Detectabilidad sobre Estimaciones del Rango Geogr´ afico de Bignonieae Resumen: El riesgo de extinci´ on no ha sido evaluado para 95% de todas las especies de plantas descritas. Debido a que la Estrategia Global para la Conservaci´ on de Plantas propone que en 2010 se cuente con evaluaciones preliminares del estado de conservaci´ on de todas las especies de plantas descritas, los especimenes de herbario (i.e., datos primarios de ocurrencia) son cada vez m´ as utilizados para inferir componentes de amenaza a partir de estimaciones de la extensi´ on del rango geogr´ afico. Sin embargo, las estimaciones de la extensi´ on del rango geogr´ afico derivadas de datos de herbario pueden ser imprecisas debido al sesgo de colecta asociado con la variaci´ on interespec´ ıfica en la detectabilidad. Utilizamos datos de 377 especies de Bignonieae para probar la hip´ otesis de que hay una relaci´ on positiva entre la detectabilidad y las estimaciones de ‡email seema.sheth@mobot.org Paper submitted March 2, 2007; revised manuscript accepted July 11, 2007. 200 Conservation Biology, Volume 22, No. 1, 200–211 C 2008 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2007.00858.x