Fecundity as a Basis for Risk Assessment of Nonindigenous Freshwater Molluscs REUBEN P. KELLER, ∗ ‡ JOHN M. DRAKE, ∗ § AND DAVID M. LODGE† ∗∗ ∗ Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, U.S.A. †National Center for Ecological Analysis and Synthesis, 735 State Street Suite 300, Santa Barbara, CA 93101, U.S.A. Abstract: The most efficient way to reduce future damages from nonindigenous species is to prevent the introduction of harmful species. Although ecologists have long sought to predict the identity of such species, recent methodological advances promise success where previous attempts failed. We applied recently developed risk assessment approaches to nonindigenous freshwater molluscs at two geographic scales: the Laurentian Great Lakes basin and the 48 contiguous states of the United States. We used data on natural history and biogeography to discriminate between established freshwater molluscs that are benign and those that constitute nuisances (i.e., cause environmental and/or economic damage). Two statistical techniques, logistic regression and categorical tree analysis, showed that nuisance status was positively associated with fecundity. Other aspects of natural history and biogeography did not significantly affect likelihood of becoming a nuisance. We then used the derived statistical models to predict the chance that 15 mollusc species not yet in natural ecosystems would cause damage if they become established. We also tested whether time since establishment is related to the likelihood that nonindigenous mollusc species in the Great Lakes and United States would cause negative impacts. No significant relationship was evident at the U.S. scale, but recently established molluscs within the Great Lakes were more likely to cause negative impacts. This may reflect changing environmental conditions, changing patterns of trade, or may be an indication of “invasional meltdown.” Our quantitative analyses could be extended to other taxa and ecosystems and offer a number of improvements over the qualitative risk assessments currently used by U.S. (and other) government agencies. Keywords: biological invasion, ecological forecasting, ecological prediction, mollusk, risk analysis, risk assess- ment La Fecundidad como Base para la Evaluaci´ on de Riesgo de Moluscos Dulceacu´ ıcolas No Nativos Resumen: La prevenci´ on de la introducci´ on de especies perjudiciales es la manera m´ as eficiente de reducir los da˜ nos futuros ocasionados por especies no nativas. Aunque los ec´ ologos han buscado predecir la identidad de tales especies durante mucho tiempo, avances metodol´ ogicos actuales prometen ´ exito en donde han fallado intentos anteriores. Aplicamos m´ etodos de evaluaci´ on de riesgo, desarrollados recientemente, en moluscos dul- ceacu´ ıcolas en dos escalas regionales: la cuenca Laurentian de Grandes Lagos y los 48 estados contiguos de los Estados Unidos. Utilizamos datos de historia natural y biogeograf´ ıa para discriminar moluscos dulceacu´ ıcolas establecidos que son ben´ eficos de los que son perjudiciales (i.e., causan da˜ no ambiental y/o econ´ omico). Dos t´ ecnicas estad´ ısticas, regresi´ on log´ ıstica y an´ alisis de ´ arbol categ´ orico, mostraron que el estatus perjudicial estaba asociado positivamente con la fecundidad. Otros aspectos de la historia natural y biogeograf´ ıa no alteraron la probabilidad de convertirse en perjudicial. Posteriormente utilizamos los modelos estad´ ısticos derivados para predecir la probabilidad de que 15 especies de moluscos que aun no est´ an en ecosistemas naturales pudieran causar da˜ nos en caso de establecerse. Tambi´ en probamos si el tiempo transcurrido desde el establecimiento est´ a relacionado con la probabilidad de que especies de moluscos no nativos en los Grandes Lagos y en Estados Unidos pudieran causar impactos negativos. No hubo relaci´ on significativa evidente en ‡email rkeller2@nd.edu §Current address: Institute of Ecology, University of Georgia, Athens, GA 30602, U.S.A. ∗∗ Current address: Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, U.S.A. Paper submitted December 5, 2005; revised manuscript accepted May 15, 2006. 191 Conservation Biology Volume 21, No. 1, 191–200 C 2007 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2006.00563.x