Human traffic and habitat complexity are strong predictors for the distribution of a declining amphibian

Invasive species and habitat modification threaten California's native pond-breeding amphibians, including the federally threatened California Red-legged Frog (Rana draytonii). The relative contributions of invasive species, including the American Bullfrog (Lithobates catesbeianus), and of habitat changes to these declines are disputed. I conducted a field study over several years in central California to examine the presence/absence of these two species at 79 breeding ponds to determine the predictive role for occupancy of factors including vegetation, pond characteristics, and measures of human activity. I used a boosted regression tree approach to determine the relative value of each predictor variable. Increased measures of human activity, especially proximity to trails and roads, were the best predictors for the absence of California Red-legged Frogs and California Newts. Historical factors and habitat conditions were associated with the extent and spread of the American Bullfrog. ...

入侵物种与生境改变正威胁着加利福尼亚州本土的池塘繁殖两栖动物，其中包括受美国联邦政府列为受威胁物种的加州红腿蛙（California Red-legged Frog，Rana draytonii）。入侵物种（含美洲牛蛙（American Bullfrog，Lithobates catesbeianus））与生境变化对这类两栖动物种群衰退的相对贡献仍存在争议。本研究在加利福尼亚州中部开展了为期数年的野外调查，对79个繁殖池塘内上述两个物种的存在/缺失情况进行监测，以明确植被、池塘特征、人类活动指标等因素对物种生境占据情况的预测作用。本研究采用提升回归树（boosted regression tree）方法，计算各预测变量的相对重要性。人类活动强度的提升——尤其是距离步道与道路较近——是加州红腿蛙与加州蝾螈缺失的最佳预测因子。历史因素与生境条件则与美洲牛蛙的种群扩张范围及扩散程度相关。...