Department of Fish and Wildlife Conservation, Virginia Tech, 100 Cheatham Hall, Blacksburg, Virginia 24061, USA.
Ecol Appl. 2012 Sep;22(6):1791-802. doi: 10.1890/11-0915.1.
Concern that environmental contaminants contribute to global amphibian population declines has prompted extensive experimental investigation, but individual-level experimental results have seldom been translated to population-level processes. We used our research on the effects of mercury (Hg) on American toads (Bufo americanus) as a model for bridging the gap between individual-level contaminant effects and amphibian population viability. We synthesized the results of previous field and laboratory studies examining effects of Hg throughout the life cycle of B. americanus and constructed a comprehensive demographic population model to evaluate the consequences of Hg exposure on population dynamics. Our model explicitly considered density-dependent larval survival, which is known to be an important driver of amphibian population dynamics, and incorporated two important factors that have seldom been considered in previous amphibian modeling studies: environmental stochasticity and sublethal effects. We demonstrated that decreases in embryonic survival and sublethal effects (e.g., reduced body size) that delay maturation have minor effects on population dynamics, whereas contaminant effects that reduce late-larval or post-metamorphic survival have important population-level consequences. We found that excessive Hg exposure through maternal transfer or larval diet, alone, had minor effects on B. americanus populations. Simultaneous maternal and dietary exposure resulted in reduced population size and a dramatic increase in extinction probability, but explicit prediction of population-level effects was dependent on the strength of larval density dependence. Our results suggest that environmental contaminants can influence amphibian population viability, but that highly integrative approaches are needed to translate individual-level effects to populations.
对环境污染物导致全球两栖动物种群减少的担忧促使人们进行了广泛的实验研究，但个体水平的实验结果很少转化为种群水平的过程。我们使用对汞（Hg）对美洲牛蛙（Bufo americanus）影响的研究作为一个模型，来弥合个体水平污染物效应与两栖动物种群生存力之间的差距。我们综合了以前研究 Hg 对 B. americanus 生命周期影响的现场和实验室研究结果，并构建了一个综合的人口动态模型，以评估 Hg 暴露对种群动态的后果。我们的模型明确考虑了密度依赖的幼体存活率，这是已知的影响两栖动物种群动态的重要驱动因素，并且纳入了以前的两栖动物建模研究中很少考虑的两个重要因素：环境随机性和亚致死效应。我们证明，胚胎存活率降低和亚致死效应（例如，体型减小）会延迟成熟，对种群动态的影响较小，而减少晚期幼虫或变态后生存的污染物效应对种群水平具有重要的后果。我们发现，通过母体转移或幼虫饮食单独暴露于过量 Hg 对 B. americanus 种群的影响较小。同时进行母体和饮食暴露会导致种群规模缩小和灭绝概率急剧增加，但对种群水平效应的明确预测取决于幼虫密度依赖性的强度。我们的研究结果表明，环境污染物会影响两栖动物的种群生存力，但需要高度综合的方法才能将个体水平的效应转化为种群水平。
