Ongoing harlequin toad declines suggest the amphibian extinction crisis is still an emergency

The Anthropocene is marked by unprecedented biodiversity loss. At COP15, nearly 200 nations committed to significantly reducing extinction rates by 2050. Amphibians are among the most threatened vertebrates, facing severe population declines globally despite conservation efforts. Extinction risk is unevenly distributed; certain genera, like the Neotropical harlequin toads (*Atelopus*), exhibit exceptionally high threat levels. While recent rediscoveries of over 30 *Atelopus* species offer hope, the overall effectiveness of conservation measures remains uncertain. This study uses long-term data on harlequin toad population status to assess the current state of the amphibian extinction crisis. The harlequin toads, given their severe past declines and recent rediscoveries, represent a valuable model system to evaluate the progress of conservation efforts. The research will analyze trends in population status, assess ongoing and emerging threats, and evaluate the efficacy of mitigation strategies, ultimately determining whether the amphibian extinction crisis continues to represent an emergency.

Since the late 1990s, scientists have documented alarming amphibian population declines and crashes worldwide. The 2004 IUCN Global Amphibian Assessment highlighted a significant proportion of threatened and extinct species. The current IUCN Red List shows a concerning percentage of threatened amphibians, emphasizing the ongoing crisis. Beyond traditional threats (habitat loss, degradation), novel and synergistic stressors such as climate change and emerging infectious diseases (e.g., chytridiomycosis caused by *Batrachochytrium dendrobatidis*) exacerbate the situation. The IUCN Amphibian Conservation Action Plan outlines strategies for addressing this emergency, including research, monitoring, habitat protection, disease mitigation, capacity building, and ex situ conservation breeding. Despite the ongoing discoveries of new amphibian species, accurately assessing the overall state of the amphibian crisis remains challenging due to difficulties in estimating the total number of extant species and monitoring their population trends.

This study utilized a database initially compiled by La Marca et al. (2005), updated through expert consultations (105 experts) from October 2019 to December 2022. The updated database included information on 131 *Atelopus* species (including tentatively considered subspecies), encompassing distribution, population size, trends, presence of *B. dendrobatidis*, and occurrence in protected areas. Population status was categorized as 'steady', 'shrinking', 'data pending', or 'probably vanished'. Statistical analyses (Fisher's exact test) compared population status data from 2004 and 2022. The potential impact of climate change was assessed using the Climate Stability Index (CSI), considering the SSP 8.5 scenario. Data on *Atelopus* conservation breeding efforts were gathered from relevant institutions worldwide. The methodology involved multiple rounds of expert consultations to refine population estimates and trends, acknowledging inherent uncertainty in expert assessments. Taxonomical considerations were meticulously addressed to ensure accurate species-level analyses, addressing ongoing taxonomic challenges within the *Atelopus* genus. The inclusion of species not formally described yet recognized in expert assessments enhanced the comprehensiveness of the analysis.

Comparison of the 2004 and 2022 datasets showed no significant improvement in the overall population status of *Atelopus* species. No species exhibited an improvement in status from 'shrinking' to 'steady'. While some rediscoveries have occurred since 2004, these do not necessarily represent true population recoveries, many rediscovered species were subsequently lost. Habitat destruction and degradation, along with the presence of *B. dendrobatidis*, remain major threats impacting a significant number of species. Climate change is projected to pose an additional and potentially substantial threat in the future, especially for high-altitude species. Despite the increased number of *Atelopus* species within protected areas, the ongoing population declines indicate that protection alone is insufficient. Captive breeding programs have been implemented for several species, with varying degrees of success. Regional biases in breeding efforts are observed, with certain geographic areas lacking adequate conservation breeding initiatives.

This study's findings directly challenge the hypothesis that the harlequin toad populations are entering a post-decline recovery phase. The lack of improvement in overall population status highlights the continuing crisis for this group and suggests that current conservation efforts have not been effective enough to reverse the declining trend. Habitat loss and chytridiomycosis remain significant threats, while climate change is anticipated to further exacerbate the situation. The continued existence of these threats combined with limited success in captive breeding emphasizes the need for a more comprehensive and urgently scaled approach to amphibian conservation. The success of individual efforts in captive breeding programs illustrates the effectiveness of this strategy, but regional inconsistencies emphasize the need for improvement and expansion of such programs.

The persistent declines in harlequin toad populations, despite conservation efforts, strongly indicate that the amphibian extinction crisis is far from over. While rediscoveries offer a glimmer of hope, they do not equate to population recovery. The continued prevalence of habitat destruction, *B. dendrobatidis*, and the impending threat of climate change demand a significant intensification of conservation efforts. This necessitates a multi-pronged approach encompassing habitat protection and restoration, innovative disease management techniques, and enhanced and expanded ex situ conservation breeding programs. Future research should focus on developing and implementing more effective mitigation strategies tailored to specific threats and geographic contexts.

The reliance on expert knowledge in assessing population status introduces an element of uncertainty. While efforts were made to standardize data collection and minimize bias through multiple rounds of expert consultation, inherent subjectivity remains. The projection of future climate change impacts relies on models, which can have uncertainties and limitations. Further limitations are associated with the availability of data on the presence of *B. dendrobatidis* infection for some species and uncertainty around the actual extinction versus unconfirmed loss status of certain populations.