The western pond turtle (WPT), recently separated into two paripatrically distributed species (Emys pallida and Emys marmorata), is experiencing significant reductions in its range and population size. In addition to habitat loss, two potential causes of decline are female-biased road mortality and high juvenile mortality from non-native predatory bullfrogs (Rana catesbeiana). However, quantitative analyses of these threats have never been conducted for either species of WPT. We used a

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... on of historical museum samples and published and unpublished field studies shared with us through personal communications with WPT field researchers (B Shaffer, P Scott, R Fisher, C Brown, R Dagit, L Patterson, T Engstrom, 2019, personal communications) to quantify the effect of roads and bullfrogs on WPT populations along the west coast of the United States. Both species of WPT shift toward increasingly male biased museum collections over the last century, a trend consistent with increasing, female-biased road mortality. Recent WPT population studies revealed that road density and proximity were significantly associated with increasingly male-biased sex ratios, further suggesting female-biased road mortality. The mean body size of museum collections of E. marmorata, but not E. pallida, has increased over the last 100 years, consistent with reduced recruitment and aging populations that could be driven by invasive predators. Contemporary WPT population sites that co-occur with bullfrogs had significantly greater average body sizes than population sites without bullfrogs, suggesting strong bullfrog predation on small WPT hatchlings and juveniles. Overall, our findings indicate that both species of WPT face demographic challenges which would have been difficult to document without the use of both historical data from natural PeerJ reviewing PDF | (Manuscript to be reviewed history collections and contemporary demographic field data. Although correlational, our analyses suggest that female-biased road mortality and predation on small turtles by nonnative bullfrogs are occurring, and that conservation strategies reducing both may be important for WPT recovery. Abstract 44 The western pond turtle (WPT), recently separated into two paripatrically distributed species 45 (Emys pallida and Emys marmorata), is experiencing significant reductions in its range and 46 population size. In addition to habitat loss, two potential causes of decline are female-biased road 47 mortality and high juvenile mortality from non-native predatory bullfrogs (Rana catesbeiana). 48 However, quantitative analyses of these threats have never been conducted for either species of 49 WPT. We used a combination of historical museum samples and published and unpublished field 50 studies shared with us through personal communications with WPT field researchers (B Shaffer, 51 P Scott, R Fisher, C Brown, R Dagit, L Patterson, T Engstrom, 2019, personal communications) 52 to quantify the effect of roads and bullfrogs on WPT populations along the west coast of the 53 United States. Both species of WPT shift toward increasingly male biased museum collections 54 over the last century, a trend consistent with increasing, female-biased road mortality. Recent 55 WPT population studies revealed that road density and proximity were significantly associated 56 with increasingly male-biased sex ratios, further suggesting female-biased road mortality. The 57 mean body size of museum collections of E. marmorata, but not E. pallida, has increased over 58 the last 100 years, consistent with reduced recruitment and aging populations that could be 59 driven by invasive predators. Contemporary WPT population sites that co-occur with bullfrogs 60 had significantly greater average body sizes than population sites without bullfrogs, suggesting 61 strong bullfrog predation on small WPT hatchlings and juveniles. Overall, our findings indicate 62 that both species of WPT face demographic challenges which would have been difficult to 63 document without the use of both historical data from natural history collections and 64 contemporary demographic field data. Although correlational, our analyses suggest that female-65 biased road mortality and predation on small turtles by non-native bullfrogs are occurring, and 66 that conservation strategies reducing both may be important for WPT recovery.