Ziemba Julie L, Hickerson Cari-Ann M, Anthony Carl D
John Carroll University, University Heights, Ohio, United States of America.
PLoS One. 2016 May 4;11(5):e0151591. doi: 10.1371/journal.pone.0151591. eCollection 2016.
Asian pheretimoid earthworms (e.g. Amynthas and Metaphire spp.) are invading North American forests and consuming the vital detrital layer that forest floor biota [including the keystone species Plethodon cinereus (Eastern Red-backed Salamander)], rely on for protection, food, and habitat. Plethodon cinereus population declines have been associated with leaf litter loss following the invasion of several exotic earthworm species, but there have been few studies on the specific interactions between pheretimoid earthworms and P. cinereus. Since some species of large and active pheretimoids spatially overlap with salamanders beneath natural cover objects and in detritus, they may distinctively compound the negative consequences of earthworm-mediated resource degradation by physically disturbing important salamander activities (foraging, mating, and egg brooding). We predicted that earthworms would exclude salamanders from high quality microhabitat, reduce foraging efficiency, and negatively affect salamander fitness. In laboratory trials, salamanders used lower quality microhabitat and consumed fewer flies in the presence of earthworms. In a natural field experiment, conducted on salamander populations from "non-invaded" and "pheretimoid invaded" sites in Ohio, salamanders and earthworms shared cover objects ~60% less than expected. Earthworm abundance was negatively associated with juvenile and male salamander abundance, but had no relationship with female salamander abundance. There was no effect of pheretimoid invasion on salamander body condition. Juvenile and non-resident male salamanders do not hold stable territories centered beneath cover objects such as rocks or logs, which results in reduced access to prey, greater risk of desiccation, and dispersal pressure. Habitat degradation and physical exclusion of salamanders from cover objects may hinder juvenile and male salamander performance, ultimately reducing recruitment and salamander abundance following Asian earthworm invasion.
亚洲环毛蚓（如远盲蚓属和后孔寡毛属物种）正在入侵北美森林，并消耗至关重要的碎屑层，而森林地表生物群落（包括关键物种灰红背无肺螈）依赖该碎屑层提供保护、食物和栖息地。几种外来蚯蚓物种入侵后，灰红背无肺螈的种群数量下降与落叶层损失有关，但关于环毛蚓与灰红背无肺螈之间的具体相互作用的研究很少。由于一些大型且活跃的环毛蚓物种在自然覆盖物下方和碎屑中与蝾螈在空间上重叠，它们可能会通过干扰蝾螈的重要活动（觅食、交配和孵卵），显著加剧蚯蚓介导的资源退化的负面影响。我们预测蚯蚓会将蝾螈排除在高质量微生境之外，降低觅食效率，并对蝾螈的适合度产生负面影响。在实验室试验中，蝾螈在有蚯蚓的情况下会使用质量较低的微生境，并且消耗的苍蝇数量更少。在一项针对俄亥俄州“未入侵”和“环毛蚓入侵”地点的蝾螈种群进行的自然野外实验中，蝾螈和蚯蚓共用覆盖物的比例比预期少约60%。蚯蚓的丰度与幼年和成年雄性蝾螈的丰度呈负相关，但与成年雌性蝾螈的丰度没有关系。环毛蚓入侵对蝾螈的身体状况没有影响。幼年和非本地成年雄性蝾螈不会在岩石或原木等覆盖物下方建立稳定的领地，这导致它们获取猎物的机会减少、脱水风险增加以及扩散压力增大。栖息地退化以及蝾螈被从覆盖物中物理性排除可能会阻碍幼年和成年雄性蝾螈的表现，最终导致亚洲蚯蚓入侵后幼体补充数量减少和蝾螈数量下降。
