Estimating survival for elusive juvenile pond‐breeding salamanders

Juvenile vital rates have important effects on population dynamics for many species, but this demographic is often difficult to locate and track. As such, we frequently lack reliable estimates of juvenile survival, which are necessary for accurately assessing population stability and potential management approaches to conserve biodiversity. We empirically estimated survival rates for elusive juveniles of 3 complex lifecycle species of salamanders (ringed salamander [Ambystoma annulatum], spotted slamander [A. maculatum], and small-mouthed slamander [A. texanum]) using 2 approaches. First, we conducted an 11-month mark-recapture study within semi-natural enclosures and used Bayesian Cormack-Jolly-Seber models to estimate survival and recapture probabilities. Second, we inferred the expected annual juvenile survival rate given published vital rates for pre-metamorphic and adult ambystomatids assuming stable population growth. For all 3 species, juvenile survival probabilities were constant across recapture occasions, while recapture probability estimates were time-dependent. Further, survival and recapture probabilities among study species did not significantly differ. Post-study sampling revealed that the initial study period median estimate of annual survival probability (0.39) underestimated the number of salamanders known alive at 11 months. We therefore appended approximately 1 year of opportunistic data, which produced a median annual survival probability of 0.50, encompassing salamanders that we knew to have been alive. Calculation from literature values suggested a mean annual terrestrial juvenile ambystomatid survival probability of 0.45. Similar results among our approaches indicated that juvenile survival estimates for the study species were robust and likely comparable to rates in nature. These estimates can now be confidently applied to research, monitoring, and management efforts for the study species and ecologically similar taxa. Our data indicated that similarly robust vital rate estimates for subsets of ecologically and phylogenetically similar species can provide reasonable surrogate demographic information to advance conservation efforts for data-deficient species.

Methods
We collected these data during an 11-month capture-mark-recapture study under semi-natural conditions. We used the Bayesian jagsUI package (Kellner 2017) in R Software 3.5.1 (R Core Team 2018) to build Cormack-Jolly-Seber models to analyze our data.

幼体生命参数对诸多物种种群动态具有重要影响，但这类种群统计学特征往往难以获取与追踪。因此，我们往往难以获得可靠的幼体存活率估算值，而该数据正是精准评估种群稳定性、制定生物多样性保护潜在管理方案的必要前提。本研究针对3种具有复杂生活史的隐栖蝾螈物种——环纹钝口螈（Ambystoma annulatum）、斑点钝口螈（A. maculatum）与小口钝口螈（A. texanum）——的幼体，通过两种方法开展存活率的经验估算。其一，在半自然围栏环境中开展为期11个月的标记重捕研究，并借助贝叶斯科马克-乔利-西伯（Cormack-Jolly-Seber）模型估算存活率与重捕概率。其二，基于已发表的钝口螈科物种变态前阶段与成体的生命参数，在假设种群增长稳定的前提下，推导得到幼体年存活率的预期值。针对3个受试物种，幼体存活率在各重捕时段均保持恒定，而重捕概率估算值则随时间变化。此外，各受试物种间的存活率与重捕概率均无显著差异。研究后采样显示，本研究初期得到的年存活率中位数估算值（0.39）低估了11个月时已知存活的蝾螈个体数量。因此，我们补充了约1年的偶遇采样数据，最终得到年存活率中位数为0.50，该数值涵盖了所有已知存活的蝾螈个体。基于文献数据的计算结果显示，钝口螈科陆栖幼体的年平均存活率为0.45。两种方法得到的结果相近，表明本研究中受试物种的幼体存活率估算结果稳健可靠，且可与自然环境中的真实存活率相媲美。上述估算结果可放心应用于受试物种及生态相似类群的相关研究、监测与保护管理工作。本研究数据表明，针对生态与系统发育相似的物种子集，通过类似方式获得的可靠生命参数估算值，可为数据匮乏物种的保护工作提供合理的替代种群统计学数据。

研究方法
本研究在半自然环境下开展为期11个月的标记重捕实验，收集相关数据。本研究使用R软件3.5.1（R开发团队, 2018）中的贝叶斯jagsUI工具包（Kellner, 2017）构建Cormack-Jolly-Seber模型，对实验数据进行分析。