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854 JULIAN D. OLDEN ET AL. Ecology, Vol. 89, No. 3 capability) compared to species principally threatened by invasive species. This finding supports the idea that the interaction between habitat loss/fragmentation and the differential dispersal ability of fish (for example to recolonize areas after disturbance) is an important mechanism driving the extinction vulnerability of native fishes in the Lower Colorado River Basin (Fagan et al. 2002). We found that fish species with "slow" life histories (e.g., large body size, long life, delayed maturity), minimal parental care to offspring, and specialized feeding behaviors face greater frequency of local extirpation and perceived extinction risk than would be predicted by simple additive effects of these traits. These species have low maximum rates of population growth and are therefore intrinsically more vulnerable to environmental change and, ultimately, extinction (Minckley 1991). Similarly, the synergistic effects of limited parental care and high trophic specialization (depicted by low diet breadth) were associated with both elevated rarity and greater frequency of local extirpa- tion, a relationship observed for freshwater fishes in other regions of North America and the world (Anger- meier 1995, Parent and Schriml 1995, Reynolds et al. 2005). Our findings also suggest that multiple traits may operate to reduce extinction risk via what could be considered trait antagonisms. As examples, fish species with "slow" life histories appear buffered from higher probabilities of extirpation if they have relatively higher fecundity, and species with low parental care may have lower extinction risk if they are feeding generalists or have a body morphology that is indicative of stronger swimming ability. Given that extinction is rarely catastrophic, but occurs incrementally as local popula- tions are lost or extirpated from portions of their geographic range, we believe that the subtle manner in which trait synergisms and antagonisms influence different stages of extinction risk requires further investigation. Our results reveal strong concordance between traits associated with "slow" life histories, low parental care and specialized diets, and levels of species rarity, decreased population persistence (i.e., frequency of extirpation) and decreased species persistence (i.e., extinction risk). This finding lends support to ecological theory positing that the attributes of species associated with their rarity (in this case referring to species range size and not low abundance) will further predispose them to local extirpation and global extinction (Pimm et al. 1988, Gaston 1994, Johnson 1998). Species possess- ing such traits may, therefore, be prone to the multiple jeopardies resulting from the combination of smaller population size, narrow environmental tolerances, and long recovery times following environmental change (Lawton and May 1995). Indeed, many of the most imperiled native fishes in the Lower Colorado River Basin that exhibit these trait syndromes, including G. cypha (humpback chub), bonytail, Ptychocheilus lucius (Colorado pikeminnow) and Xyrauchen texanus (razor- back sucker), have shown precipitous declines over the past century (Fagan et al. 2005b, Olden and Poff 2005). Native fish populations of the American Southwest are adversely impacted by three major factors: loss and fragmentation of riverine habitats, hydrologic alteration and water development, and invasive species. Resource managers and ecologists are faced with the difficult task of identifying those species and watersheds having greatest need for conservation, while being constrained by limited biological and environmental data. Our study suggests that the conservation of native fish species in the Lower Colorado River Basin would be informed by a trait-based approach that assesses the multiple stages and sources of extinction risk (see also Winemiller 2005). The ability to reliably predict rarity and likelihood of extirpation of a species on the basis of biological traits will allow more efficient prioritization of conservation initiatives. For example, we found that a number of fish species have trait compositions that apparently predis- pose them to higher eventual extinction risk than they are currently facing, including desert sucker, roundtail chub and Gila chub. These species are currently not listed by U.S. Fish and Wildlife Service (1999) and are considered not threatened or not evaluated by the IUCN (with the exception of Gila chub which is ranked as "lower risk"; see footnote 5). Our analysis of the intrinsic attributes of these species indicates that their conservation ranking should be reconsidered. This trait- based recommendation is supported by Fagan et al. (2005b), who convincingly showed, using century-long distributional data and the IUCN ranking scheme, that Gila chub should be re-ranked as critically endangered and desert sucker should be added to the lower risk category. CONCLUSION Meeting conservation challenges in the Lower Colo- rado River Basin will require strategies that identify and conserve fish species that face the greatest risk of extinction. Management strategies should be based on a fundamental understanding of how species' ecological attributes interact with fluvial habitats to influence population persistence in the face of environmental change. Local habitat restoration and removal/exclusion of invasive species from critical native habitats, such as spawning and nursery floodplains (Minckley et al. 2003), will only be successful if other environmental impacts that contribute to rarity, such as dam-altered flow or thermal regimes, are also mitigated (Olden et al. 2006). In short, integrative conservation plans that aim to inform and prioritize management efforts in the Lower Colorado River Basin require actions that are congruent with the life-history requirements of multiple species over large spatial and temporal scales. Our results point strongly to the need to explicitly consider trait interactions when making predictions about species vulnerability on the basis of intrinsic