Conservation translocations—the release of individuals to reestablish, augment, or newly establish populations—are increasingly used to address the biodiversity crisis (Seddon, 2010; IUCN, 2013). Reintroduction biology, however, is beset with tensions between traditional actions to restore historical habitat and more novel approaches that incorporate environmental change (Corlett, 2016; Taylor et al., 2017). For example, historical distributions typically drive decisions on where to direct translocation efforts, yet these baselines decline in relevancy in rapidly changing ecosystems (Forbes et al., 2020). A more innovative approach to translocations is to target habitats that are becoming more appropriate for some species, even in the absence of evidence for historical occupancy (Peterson St-Laurent et al., 2021). Yosemite National Park (Yosemite) and the broader Sierra Nevada Mountains encompass elevational gradients and biodiversity patterns that can facilitate shifting species ranges and, therefore, accommodate conservation translocations (Singer, Papouchis, & Symonds, 2000; Powell et al., 2013; Elsen, Monahan, & Merenlender, 2018; Joseph & Knapp, 2018). The threatened California red-legged frog (Rana draytonii) was extirpated from Yosemite National Park by the 1970s (Adams et al., 2023). To successfully translocate the species back to its known historical range in Yosemite, non-native, predatory American bullfrogs (Lithobates catesbeianus; hereafter “bullfrogs”) needed to first be eradicated. In 2016, bullfrog eradication was underway, but the R. draytonii source population was tenuous; therefore, translocation could not wait for eradication to be completed. We opted to translocate R. draytonii to Yosemite Valley (Valley), where suitable habitat was present, even though we were in a limited-knowledge state, with a lack of historical evidence for the species' occurrence in the Valley (Adams et al., 2023). Our aim was to proactively assist adaptation to a changing climate and protect the species from continued habitat loss by providing a safe harbor for the species in an area that is protected from many of the species' threats, including drought, urbanization, agriculture, and non-native predators (U.S. Fish and Wildlife Service, 2022). Safe harbor populations can also provide insurance against pathogens such as the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd) which is present in the Valley (De Castro & Bolker, 2005; Adams, Bushell, & Grasso, 2022), and to which R. draytonii is susceptible (Adams et al., 2020). We incorporated an ex situ component of the reintroduction program at the San Francisco Zoo, including a Bd inoculation study (Adams, Bushell, & Grasso, 2022) and optimization of husbandry techniques for R. draytonii, which had not been reared in captivity before. The captive-reared frogs have subsequently contributed significantly to the establishment of an introduced population in Yosemite Valley. We were faced with whether to attempt to maintain historical species assemblages, or whether to allow species to shift with a dynamic landscape in concert with a changing climate. The dynamic nature of ecosystems, coupled with uncertainties beset by knowledge gaps and climate change, mean that justifying restoration goals with literal historical states is problematic (Rohwer & Marris 2016). Because of its high elevation and water-retaining capacity through snow, the Sierra Nevada is targeted as a climate change refugium for many taxa (Balantic et al., 2021). At 900–1280 m.a.s.l., the Valley is in the upper range of the R. draytonii elevational occurrence in the USA (1500 m; Jennings & Hayes, 1994), though the species occurs at 2100 m in Baja California, Mexico (Peralta-Garcia et al., 2016). Historically, protecting and restoring native species in U.S. National Parks was based on specific definitions of native species as those occurring in particular spatiotemporal configurations. Binary descriptions of the native/invasive species paradigm are derived from colonial timelines and perspectives and exclude more diverse worldviews which may consider species movements as neutral (Reo & Ogden, 2018). The R. draytonii translocation, which uses an as-yet novel approach to management, has allowed us to provide a safe harbor for the species by integrating and correcting for the complexities of change over time rather than attempting to restore populations to an idealized, but inaccurate, historical state. The concern that assisted migration could result in a new invasive species is relevant. We argue, however, that translocating R. draytonii to the Valley was a low-risk endeavor. We began our translocations at a small scale and translocated a species with little invasion risk. Assisted migration has also been deemed too expensive by many experts (Hagerman et al., 2010); however, we were able to do egg mass translocations successfully at a relatively minimal cost. This phenomenon may be somewhat unique to amphibians, in which large numbers of eggs statistically destined to predation can be put toward conservation. Reliance on historical reference points limits managers' effectiveness in conserving species on a changing planet. By instead working with the dynamic and stochastic nature of anthropogenic environmental change and taking an open-minded approach to novel methods and dramatic interventions, managers can resist the conceptual shortcomings that have limited the effectiveness of traditional conservation methods (Kareiva & Fuller, 2016). For example, counterfactuals can provide a shifted reference frame for translocation decision making (Bull et al., 2014). Without the goal of translocating R. draytonii to the Valley, the motivation for the extensive, challenging undertaking of eradicating bullfrogs from the site (Kamoroff et al., 2020) is unlikely to have existed. Successful wild breeding and recruitment of R. draytonii have occurred in the Valley from 2019 to 2022. Now that the translocations have taken root, the site can continue to provide a safe harbor for future reintroductions elsewhere in the region. Both management agencies and biodiversity can benefit from policies and attitudes that allow for more flexibility and risk when choosing actions to address environmental change in the stochastic Anthropocene (Kareiva & Fuller, 2016). In the animal conservation arena, broader research agendas that implement a more expansive approach can include examining institutional and sociocultural attitudes toward different conservation options as well as conducting pilot studies that test bold, on-the-ground conservation actions before implementing them at a larger scale. Our successful translocation illustrates that suitable habitat can provide a safe harbor for an endangered species even if it is marginally outside of the historical range. This action is an intrepid forward step for the U.S. National Park Service to lead the way for novel approaches to restoration in a perennially dynamic future.
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