Data from: High adult mortality in disease-challenged frog populations increases vulnerability to drought

Pathogen emergence can drive major changes in host population demography, with implications for population dynamics and sensitivity to environmental fluctuations. The amphibian disease chytridiomycosis, caused by infection with the fungal pathogen Batrachochytrium dendrobatidis (Bd), is implicated in the severe decline of over 200 amphibian species. In species that have declined but not become extinct, Bd persists and can cause substantial ongoing mortality. High rates of mortality associated with Bd may drive major changes in host demography, but this process is poorly understood. Here, we compared population age structure of Bd-infected populations, Bd-free populations and museum specimens collected prior to Bd emergence for the endangered Australian frog, Litoria verreauxii alpina (alpine tree frog). We then used population simulations to investigate how pathogen-associated demographic shifts affect the ability of populations to persist in stochastic environments. We found that Bd-infected populations have a severely truncated age structure associated with very high rates of annual adult mortality. Near-complete annual adult turnover in Bd-infected populations means that individuals breed once, compared with Bd-free populations where adults may breed across multiple years. Our simulations showed that truncated age structure erodes the capacity of populations to withstand periodic recruitment failure; a common challenge for species reproducing in uncertain environments. We document previously undescribed demographic shifts associated with a globally emerging pathogen and demonstrate how these shifts alter host ecology. Truncation of age structure associated with Bd effectively reduces host niche width and can help explain the contraction of L. v. alpina to perennial waterbodies where the risk of drought-induced recruitment failure is low. Reduced capacity to tolerate other sources of mortality may explain variation in decline severity among other chytridiomycosis-challenged species and highlights the potential to mitigate disease impacts through minimizing other sources of mortality.病原体的出现可引发宿主种群人口统计学特征的显著改变，并对种群动态及环境波动敏感性产生深远影响。由真菌病原体蛙壶菌（Batrachochytrium dendrobatidis, Bd）感染引发的两栖动物壶菌病，已被证实与全球200余种两栖动物的严重种群衰退密切相关。在已出现衰退但未灭绝的两栖动物物种中，Bd仍持续存在，并可造成持续的高死亡率。与Bd感染相关的高死亡率或可引发宿主种群人口统计学特征的显著改变，但目前学界对这一过程的认知仍较为匮乏。 本研究以濒危的澳大利亚蛙类高山雨滨蛙（Litoria verreauxii alpina）为研究对象，对比了感染Bd的种群、未感染Bd的种群，以及Bd出现前馆藏标本的种群年龄结构。随后，我们通过种群模拟实验，探究了与病原体相关的人口统计学特征变化如何影响种群在随机波动环境中的存续能力。 研究结果显示，感染Bd的种群年龄结构存在严重截断现象，这与极高的成体年死亡率密切相关。感染Bd的种群中成体年更替率接近完全，个体仅能繁殖一次；而未感染Bd的种群中，成体可连续多年参与繁殖。 我们的模拟实验表明，年龄结构截断会削弱种群抵御周期性种群补充失败的能力——这是在不确定环境中繁殖的物种所面临的普遍挑战。 本研究记录了与全球新兴病原体相关的、此前未被报道的种群人口统计学特征变化，并阐明了此类变化如何改变宿主的生态特征。与Bd感染相关的年龄结构截断，可有效缩小宿主的生态位宽度，这一发现有助于解释高山雨滨蛙（L. v. alpina）的分布范围为何收缩至常年性水体——这类环境中干旱引发的种群补充失败风险较低。 种群抵御其他致死因素的能力下降，或可解释其他受壶菌病威胁的两栖动物种群衰退严重程度存在差异的原因，同时也凸显了通过降低其他致死因素的影响，以缓解病害危害的潜在可能。