Dataset Information

Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders.

ABSTRACT: 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.

SUBMITTER: Ziemba JL

PROVIDER: S-EPMC4856329 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders.

Ziemba Julie L JL Hickerson Cari-Ann M CA Anthony Carl D CD

PloS one 20160504 5

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 betwee ...[more]

PMID: 27144403

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Project description:Balancing timber production and conservation in forest management requires an understanding of how timber harvests affect wildlife species. Terrestrial salamanders are useful indicators of mature forest ecosystem health due to their importance to ecosystem processes and sensitivity to environmental change. However, the effects of timber harvests on salamanders, though often researched, are still not well understood. To further this understanding, we used artificial cover objects to monitor the relative abundance of terrestrial salamanders for two seasons (fall and spring) pre-harvest and five seasons post-harvest in six forest management treatments, and for three seasons post-harvest across the edge gradients of six recent clearcuts. In total, we recorded 19,048 encounters representing nine species of salamanders. We observed declines in mean encounters of eastern red-backed salamanders (Plethodon cinereus) and northern slimy salamanders (P. glutinosus) from pre- to post-harvest in group selection cuts and in clearcuts. However, we found no evidence of salamander declines at shelterwoods and forested sites adjacent to harvests. Edge effects induced by recent clearcuts influenced salamanders for approximately 20 m into the forest, but edge influence varied by slope orientation. Temperature, soil moisture, and canopy cover were all correlated with salamander counts. Our results suggest silvicultural techniques that remove the forest canopy negatively affect salamander relative abundance on the local scale during the years immediately following harvest, and that the depth of edge influence of clearcuts on terrestrial salamanders is relatively shallow (<20 m). Small harvests (<4 ha) and techniques that leave the forest canopy intact may be compatible with maintaining terrestrial salamander populations across a forested landscape. Our results demonstrate the importance of examining species-specific responses and monitoring salamanders across multiple seasons and years. Long-term monitoring will be necessary to understand the full impacts of forest management on terrestrial salamanders.

Project description:The invasive Asian earthworms, Amynthas tokioensis and A. agrestis, have been successful in entering North American forests in recent decades, with significant damage to both soils and above-ground environments. This success could be driven in part by a polyploid genetic system and parthenogenetic reproduction, often suggested as benefits for invasive species. Therefore, we assessed the genetic population structure, genetic diversity, and reproductive system of both species using morphological traits and panels of microsatellite markers. A total of 216 A. tokioensis and 196 A. agrestis from six sites in Vermont USA were analyzed. Although all worms were morphologically hermaphroditic, all the A. agrestis lacked the male pore (the structure allowing pass of sperm between individuals), and only 19% of the A. tokioensis possessed the male pore. All A. tokioensis earthworms were triploid (scored for three alleles for at least 1 locus, and usually several), and A. agrestis was a mix of triploid and diploid individuals. Notable was the high proportion (80%) of A. agrestis earthworms that were diploid at one site. There was clearly clonal reproduction, with identical seven- locus genotypes observed for earthworms from each site, with as many as 45 individuals with the identical genotype at one site. However, the earthworms were also genetically diverse, with 14 genotypes observed for A. tokioensis and 54 for A. agrestis, and with many singleton genotypes (a single individual). Most genotypes (71% for A. tokioensis and 92% for A. agrestis) were found at a single site. The greatest number of genotypes was found at a commercial nursery where fully 23/26 A. agrestis earthworms were singleton genotypes. As expected for the pattern of private clone alleles at sites, several measures of geographic genetic differentiation were positive, and as expected for triploid systems, an AMOVA analysis showed high within-individual genetic diversity. The paradox of clear clonal reproduction, but with a great number of genotypes for each species, and the mix of triploid and diploid individuals could be explained if the worms have been sexually reproductive, with the switch to the uniparental system only recently (or even if sexual reproduction is episodic). Last, a large number of microsatellite loci were recovered for each species and there sequence and suggested PCR primers are provided for free use by other researchers.

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Dataset Information

Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders.

Publications

Invasive Asian Earthworms Negatively Impact Keystone Terrestrial Salamanders.

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