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In northern North America, invasive earthworms (including the nightcrawler Lumbricus terrestris) have been dispersing from points of introduction and dramatically affecting soil structure, soil food webs, and forest floor dynamics. However, little is known about the factors influencing the local distribution of invasive earthworms south of the Wisconsinan glaciation. Earthworms were sampled at suspected sites of introduction near Mountain Lake Biological Field Station, Virginia, USA. The density of invasive earthworms decreased as distance from suspected sites of introduction increased; native earthworms displayed the opposite relationship. However, the distance that L. terrestris was found into the forest was less than expected given dispersal rates calculated from more northern invasions. We also found correlations among population densities of L. terrestris and physical-chemical properties of the soil, and differences between field and forest soils in terms of temperature, moisture, and soil chemical properties. We conducted two experiments to analyze some factors possibly responsible for the observed distribution: (1) temperature and moisture, and (2) soil type (field vs. forest) and food resources. Our results suggest that L. terrestris may not disperse as far into forested habitats of the Southern Appalachians compared to northern forests due to local physical-chemical soil characteristics. [ABSTRACT FROM AUTHOR]

Background Introduced earthworms are widespread in forests of North America creating significant negative impacts on forest understory communities. However, much of the reported evidence for negative earthworm effects comes from field investigations either comparing invaded and non-invaded forests or across invasion fronts. While important, such work is rarely able to capture the true effect of earthworms on individual plant species because most forests in North America simultaneously face multiple stressors which may confound earthworm impacts. We used a mesocosm experiment to isolate effects of the anecic introduced earthworm, Lumbricus terrestris L. on seedlings of 14 native plant species representing different life form groups (perennial herb, graminoid, and tree). Results Earthworm presence did not affect survival, fertility or biomass of any of the seedling plant species tested over a 17-week period. However, L. terrestris presence significantly decreased growth of two sedges (Carex retroflexa Muhl. ex Willd. and Carex radiata (Wahlenb.) Small) by decreasing the number of culms. Conclusions Our mesocosm results with seedlings contrast with field reports indicating extensive and significant negative effects of introduced earthworms on many mature native forbs, and positive effects on sedges. We suggest that earthworm impacts are context- and age-specific and that generalizations about their impacts are potentially misleading without considering and manipulating other associated factors. [ABSTRACT FROM AUTHOR]

Abstract: The common earthworm Lumbricus terrestris L. is an invasive species that was introduced to North America by European settlers. Subsequently, earthworms have been distributed by human activity, invaded a wide geographic range and changed previously earthworm-free ecosystems. In the present study we analyzed seven European and four North American populations from a wide geographic range at three formerly described nuclear microsatellite markers. All three markers produced multi-banding patterns and marker presence versus absence was scored in 88 narrow size intervals. Similar levels of genetic variation were observed for North American (Nei''s gene diversity = 0.058, Shannon''s I = 0.100) and European populations (Nei''s gene diversity = 0.064, Shannon''s I = 0.104). North American populations showed a higher similarity among each other than European populations in accordance with their recent introduction to North America. The relatively high level of genetic variation in North American populations and the high similarity among each other suggest their establishment from genetically diverse founder populations and rapid human-mediated population expansion. The source regions in Europe are still unclear from this analysis. [Copyright &y& Elsevier]

Abstract: The ranges of exotic earthworms have been expanding into previously earthworm-free areas in temperate forests of North America. These earthworms can have profound effects on soil properties and biogeochemical processes, but the rate and patterns of earthworm range expansion has received limited study. We assessed long-term (2001–2011) changes in earthworm distributions along two belt transects (60–75m long) in a northern hardwood forest in central New York. We expected long-term increases in earthworm abundance at the presumed earthworm invasion front. We also quantified earthworm populations in seven monospecific plantations of different tree species. We expected higher earthworm abundance in hardwood than conifer forests. We observed large annual fluctuations in earthworm abundance along both transects but no evidence of increasing abundance or range expansion at the earthworm fronts. At the plantation site we observed significant variation in earthworm abundance both within and among plantations, but the patterns were not consistently related to tree species composition; rather, earthworm abundance was highest in areas of higher soil pH and topographically wetter soils. Further study of environmental and biotic factors controlling the range expansion of exotic earthworms is needed at both local and regional scale. [Copyright &y& Elsevier]

Earthworm invasion in North American temperate forest reduces forest floor mass, yet the interactions between litter composition, invasive earthworm community composition, and forest floor structure and composition are not well understood. For 2 years, we compared disappearance of leaf litter in field mesocosms in which we manipulated litter composition (monocultures of Quercus rubra, Acer saccharum, and Tilia americana litter, and an equal mixture of all three) and thereby the initial litter chemistry (C, C fractions, N, Ca) in sites with and without the major litter-feeding invasive earthworm species. The disappearance of litter mass followed the same ranking at both the sites: T. americana > equal mixtures > A. saccharum ≥ Q. rubra. However, differences in disappearance rate between the sites depended on litter composition and time. The differences in mass loss among litters of different compositions were greatest at the site invaded by the large litter-feeding earthworm, Lumbricus terrestris, and especially for T. americana and the mixture. Similarly, observed disappearance of the litter mixture was faster than predicted by an additive model at the site with L. terrestris, especially for the higher quality litter component in early summer. Initial litter calcium content was the best predictor ( R ≥ 0.90) of overall litter mass remaining each year, supporting the idea of the importance of calcium in forest floor dynamics, especially in the presence of calciferous, invasive earthworms. [ABSTRACT FROM AUTHOR]

Studies examining the influence of habitat provisioning by one species on the behavior of other species can provide key insights regarding impacts of ecosystem engineers on the availability of resources to other species. More specifically, an organism’s use of additional habitat provided by ecosystem engineers may affect the interpretation of observational or demographic data. We chose to examine the possible influence of earthworms, as ecosystem engineers, on the behavior of terrestrial salamanders, common forest vertebrates in North America. We conducted two experiments in microcosms to examine whether the earthworm Lumbricus terrestris acted as an ecosystem engineer by providing additional habitat (burrows) for Plethodon cinereus, a common woodland salamander. We also examined whether the behavioral changes of the non-burrowing, fossorial P. cinereus differed across age classes. Adults and juveniles responded similarly, with both adults and juveniles found under cover objects more often when earthworms were absent and using earthworm burrows when available. Our field data supported our experimental data in that greater numbers of earthworms on field plots were associated with a lower proportion of cover objects being occupied by salamanders (i.e., salamanders were likely underground). We found no differences in the response of adults and juveniles to the presence of earthworms. By providing underground habitat for a common terrestrial amphibian, the presence of earthworms may impact demographic studies on salamanders and conclusions drawn from those studies regarding aboveground faunal communities in eastern North America. [ABSTRACT FROM AUTHOR]