Evidence of damage from exotic invasive earthworm activity was highly correlated to sugar maple dieback in the Upper Great Lakes region

Multiple invasion routes have led to the pervasive introduction of earthworms in North America

Soil-dwelling organisms play a key role in ecosystem functioning and the delivery of ecosystem services. As a consequence, soil taxa such as earthworms are iconic in good land management practices. However, their introduction in places where species did not co-evolve with them can trigger catastrophic changes. This issue has been largely ignored so far in nature management policies because of the positive image of soil taxa and the lack of knowledge of the magnitude of soil fauna introductions outside their native range. Here we address this gap with a large spatio-temporal database of introduced alien earthworms. We show that 70 alien earthworm species have colonized the North American continent. They have larger geographical ranges than native species and novel ecological functions, representing a serious threat to the biodiversity and functioning of native ecosystems. The probably continuous introduction of alien earthworms, from a variety of sources and introduction pathways, into many distant and often empty niches, contrasts with the classical patterns of invasions in most aboveground taxa. This suggests that earthworms, and probably other soil organisms, constitute a major but overlooked pool of invasive species that are not adequately managed by existing control and mitigation strategies.

Decline and fall of the Ediacarans: late-Neoproterozoic extinctions and the rise of the modern biosphere

The end-Neoproterozoic transition marked a gradual but permanent shift between distinct configurations of Earth's biosphere. This interval witnessed the demise of the enigmatic Ediacaran Biota, ushering in the structured trophic webs and disparate animal body plans of Phanerozoic ecosystems. However, little consensus exists on the reality, drivers, and macroevolutionary implications of end-Neoproterozoic extinctions. Here we evaluate potential drivers of late-Neoproterozoic turnover by addressing recent findings on Ediacaran geochronology, the persistence of classical Ediacaran macrobionts into the Cambrian, and the existence of Ediacaran crown-group eumetazoans. Despite renewed interest in the possibility of Phanerozoic-style 'mass extinctions' in the latest Neoproterozoic, our synthesis of the available evidence does not support extinction models based on episodic geochemical triggers, nor does it validate simple ecological interpretations centred on direct competitive displacement. Instead, we argue that the protracted and indirect effects of early bilaterian innovations, including escalations in sediment engineering, predation, and the largely understudied impacts of reef-building, may best account for the temporal structure and possible selectivity of late-Neoproterozoic extinctions. We integrate these processes into a generalised model of early eumetazoan-dominated ecologies, charting the disruption of spatial and temporal isotropy on the Ediacaran benthos as a consequence of diversifying macrofaunal interactions. Given the nature of resource distribution in Ediacaran ecologies, the continuities among Ediacaran and Cambrian faunas, and the convergent origins of ecologically disruptive innovations among bilaterians we suggest that the rise of Phanerozoic-type biotas may have been unstoppable.

Holes in the tundra: Invasive earthworms alter soil structure and moisture in tundra soils

Human introductions have resulted in earthworms establishing in the Arctic, species known to cause cascading ecosystem change. However, few quantitative outdoor experiments have been performed that describe how these soil modifying earthworms are reshaping structures in tundra soils. In this study, we used three-dimensional (3-D) X-ray images of soil cores (approximately 10 cm diameter, 20 cm height, N = 48) to assess how earthworms (Aporrectodea sp. and Lumbricus sp.) affect soil structure and macropore networks in an outdoor mesocosm experiment that lasted four summers. Effects were assessed in both shrub-dominated (heath) and herb-dominated (meadow) tundra. Earthworms almost doubled the macroporosity in meadow soils and tripled macroporosity in heath. Interestingly, the fractal dimension of macropores decreased in response to earthworm burrowing in both systems, indicating that the presence of earthworms reduced the geometric complexity in comparison to other pore-generating processes active in the tundra. Observed effects on soil structure occurred along with a dramatically reduced soil moisture content, which was observed the first winter after earthworm introduction in the meadow. Our findings suggest that predictions of future changes in vegetation and soil carbon pools in the Arctic should include major impacts on soil properties that earthworms induce.

Non-Native Earthworms Invade Forest Soils in Northern Maine, USA

Non-native earthworms can cause abrupt changes in forest ecosystems by altering soil properties and depleting or redistributing soil carbon (C) stocks. The forests of Northern Maine are often perceived as having winters that are too harsh to support earthworm populations and that earthworms are restricted to more southerly regions. In this study, we report the discovery of European earthworms at two research sites in Northern Maine. At one site, earthworms were only found across a portion of the forest, and the median organic (O) horizon C stock in the area with earthworms was 34% less than that of areas without earthworms. At a second site, earthworms were found across the entire 60-ha forest and the median O horizon C stock was 39% less than that of a similar forest without earthworms. Consistent with reports from other regions, areas with earthworms had no or minimal eluvial (E) horizons, while earthworm-free locations always had E horizons. Earthworm presence was always associated with a topsoil (A) horizon, reflecting mechanical mixing and organic matter processing by earthworms. This is one of the first reports of non-native earthworm presence in Northern Maine forests and monitoring changes in soil C will be important for determining rates of C sequestration in these forests. Warmer winter temperatures, particularly winter minimums, and greater annual precipitation will likely increase the success of new earthworm introductions across Northern Maine forests. Management actions that limit the transport of earthworms into earthworm-free areas should be carefully evaluated to minimize the potential for new introductions.

Side-swiped: Ecological cascades emanating from earthworm invasion

Non-native, invasive earthworms are altering soils throughout the world. Ecological cascades emanating from these changes stem from earthworm-caused changes in detritus processing occurring at a mid-point in the trophic pyramid, rather than the more familiar bottom-up or top-down cascades. They include fundamental changes (microcascades) in soil morphology, bulk density, nutrient leaching, and a shift to warmer, drier soil surfaces with loss of organic horizons. In North American temperate and boreal forests, microcascades cause effects of concern to society (macrocascades), including changes in CO₂ sequestration, disturbance regimes, soil quality, water quality, forest productivity, plant communities, and wildlife habitat, and facilitation of other invasive species. Interactions among these changes create cascade complexes that interact with climate change and other environmental changes. The diversity of cascade effects, combined with the vast area invaded by earthworms, lead to regionally important changes in ecological functioning.