Earthworm Populations Research Articles

Earthworms and litter management contributions to ecosystem services in a tropical agroforestry system

The development of sustainable agricultural systems depends in part upon improved management of non-crop species to enhance the overall functioning and provision of services by agroecosystems. To address this need, our research examined the role of earthworms and litter management on nutrient dynamics, soil organic matter (SOM) stabilization, and crop growth in the Quesungual agroforestry system of western Honduras. Field mesocosms were established with two earthworm treatments (0 vs. 8 Pontoscolex corethrurus individuals per mesocosm) and four litter quality treatments: (1) low-quality Zea mays, (2) high-quality Diphysa robinioides, (3) a mixture of low- and high-quality litters, and (4) a control with no organic residues applied. Mesocosms included a single Z. mays plant and additions of 15N-labeled inorganic nitrogen. At maize harvest, surface soils (0-15 cm) in the mesocosms were sampled to determine total and available P as well as the distribution of C, N, and 15N among different aggregate-associated SOM pools. Maize plants were divided into grain and non-grain components and analyzed for total P, N, and 15N. Earthworm additions improved soil structure as demonstrated by a 10% increase in mean weight diameter and higher C and N storage within large macro-aggregates (>2000 microm). A corresponding 17% increase in C contained in micro-aggregates within the macro-aggregates indicates that earthworms enhance the stabilization of SOM in these soils; however, this effect only occurred when organic residues were applied. Earthworms also decreased available P and total soil P, indicating that earthworms may facilitate the loss of labile P added to this system. Earthworms decreased the recovery of fertilizer-derived N in the soil but increased the uptake of 15N by maize by 7%. Litter treatments yielded minimal effects on soil properties and plant growth. Our results indicate that the application of litter inputs and proper management of earthworm populations can have important implications for the provision of ecosystem services (e.g., C sequestration, soil fertility, and plant production) by tropical agroforestry systems.

Hazardous Effects of Eight Years of Application of Four Organic Waste Materials on Earthworm Numbers and Biomass in Field Lysimeters

The hazardous effects on the earthworm numbers and biomass of eight consecutive yearly applications of three levels (12.5, 25, and 50 tons of dry matter/ha/y) of four different organic sludges (municipal sewage, industrial sewage, alcohol fermentation processing, and leather processing) to earthworm-free soils were examined using field lysimeters. Results were compared with those of pig manure compost (PMC)-treated soil. Of five species (Amynthas agrestis, A. sangyeoli, A. hupeiensis, Drawida koreana, and D. japonica) from 390 adult specimens collected 4 and 8 years after treatment, the number of species appeared to be lower in sludge-treated soils than in PMC-treated soils. Earthworm populations and biomass were correlated negatively with the pollution index [∑(heavy-metal concentration in soil/tolerable level)/number of heavy metal] 4 and 8 years after treatment. These results suggest that the long-term application of these sludges, particularly from industrial sewage and leather processing, might affect adversely the establishment of Megascolecid and Moniligastrid earthworms in field conditions.

Enchytraeid and earthworm communities along a pollution gradient near Olkusz (southern Poland)

The effect of heavy metal pollution on Oligochaeta ( Enchytraeidae and Lumbricidae) populations was studied along a pollution gradient in vicinity of Olkusz (southern Poland). The study sites, which differed in metal concentrations in the humus layer, were established in mixed-pine forests 3.5 km, 2.5 km, 3.9 km, 7.9 km and 31.9 km (reference site) from the source of pollution (zinc smelter). Enchytraeid and earthworm population density and species composition were determined from soil sampled four times from the study sites. Enchytraeidae populations consisted of nine genera and 18 species. The dominating enchytraeid species in all study sites was Cognettia sphagnetorum (approx. 90%), except for the most polluted site, where Enchytraeus, Fridericia and Henlea were the most common species diversity and heterogeneity were the highest in the most polluted site. The highest mean densities were found in the reference site (16,333 individuals m −2) and lowest in the most polluted site (3932 individuals m −2). Earthworm populations consisted of three epigeic species, and the most abundant one was Dendrobaena octaedra. Earthworms densities in all sites sampled were low. The concentrations of Zn, Pb and Cd in: humus layer, and in enchytraeids and earthworms, were the highest for the most polluted site and decreased with distance from pollution source. Density of Enchytraeidae and body loads of metals in Enchytraeidae and Lumbricidae can be employed for biomonitoring.

Earthworm populations in a northern U.S. Cornbelt soil are not affected by long-term cultivation of Bt maize expressing Cry1Ab and Cry3Bb1 proteins

Earthworms, which play a key role in biogeochemical processes in soil ecosystems, could be negatively affected by the cultivation of transgenic Bt crops. Studies to date have found few effects of Bt maize on earthworm species. If adverse effects occur, they are likely to be chronic or sub-lethal and expressed over large spatial and temporal scales. Our objective in the present study was to investigate potential effects on earthworm populations in soil cultivated with Bt maize in a large multiple-year field study. We surveyed the earthworm populations in 0.16-ha experimental field plots of two varieties of Cry1Ab Bt maize, one variety of Cry3Bb1 Bt maize, and three non-transgenic control varieties cultivated for four years. Four earthworm species were found in our sample: Aporrectodea caliginosa, Aporrectodea trapezoides, Aporrectodea tuberculata (collectively, the A. caliginosa species complex), and Lumbricus terrestris. We found no significant differences in the biomass of juveniles and adults for all four species between Bt and non-Bt maize varieties. From this and previous studies, we conclude that the effects of Cry1Ab and Cry3Bb1 Bt maize on the A. caliginosa species complex and L. terrestris are small. Nonetheless, general conclusions about the effects of Bt maize on earthworm populations are not warranted due to the small number of species tested. In future laboratory studies, earthworm species should be selected according to their association with a Bt crop and the impact of that species to valued soil ecosystem processes.

Effect of tillage, sampling date and soil depth on earthworm population on maize monoculture with continuous stover restitutions

Populations of the earthworm Aporrectodea caliginosa were analyzed on three sampling dates (maize emergence in spring, crop harvest in autumn and post-harvest, in winter) and two soil depths (0-15, 16-30 cm) in four tillage systems: 1) shallow tillage, 2) disk ploughing, 3) ripper decompaction (one pass) and 4) ripper decompaction (two passes). The soil was an irrigated clay loam in Central Mexico. The tillage systems were applied in winter during four consecutive years on experimental plots (400 m 2 area) cropped with maize. Tillage treatments did not cause differences in juvenile, adult and total earthworm individuals. In contrast, the sampling date had a significant effect (P < 0.05) on earthworm population: individuals were absent at maize emergence (April 2007), 135 m −2 at harvest (November 2007) and 45 m −2 at post-harvest date (January 2008). The recovery of earthworm population during the maize growing period was attributed to favourable conditions for earthworm growth consisting in abundant food (2-5 t ha −1 y −1 of maize stover) and high soil water content. Earthworm abundance showed differences caused by soil depth, individuals migrate to the deep layer after crop harvest. A very high number of burrows was observed (2200-2800 burrows m −2) at 10 cm of soil depth, in plots worked with the different tillage sequences in the three sampling dates.

Earthworm impacts on soil organic matter and fertilizer dynamics in tropical hillside agroecosystems of Honduras

Abstract Earthworms are important processors of soil organic matter (SOM) and nutrient turnover in terrestrial ecosystems. In agroecosystems, they are often seen as beneficial organisms to crop growth and are actively promoted by farmers and extension agents, yet their contribution to agroecosystem services is uncertain and depends largely on management. The Quesungual slash-and-mulch agroforestry system (QSMAS) of western Honduras has been proposed as a viable alternative to traditional slash-and-burn (SB) practices and has been shown to increase earthworm populations, yet the effect of earthworms on soil fertility and SOM in QSMAS is poorly understood. This study examined the role of Pontoscolex corethrurus in QSMAS by comparing their influence on aggregate-associated SOM and fertilizer dynamics with their effects under SB and secondary forest in a replicated field trial. Both the fertilized QSMAS and SB treatments had plots receiving additions of inorganic 15N and P, as well as plots with no inorganic N additions. Earthworm populations were manipulated in field microcosms at the beginning of the rainy season within each management treatment via additions of P. corethrurus or complete removal of existing earthworm populations. Microcosms were destructively sampled at harvest of Zea mays and soils were wet-sieved (using 53, 250 and 2000 μm mesh sizes) to isolate different aggregate size fractions, which were analyzed for total C, N and 15N. The effects of management system were smaller than expected, likely due to disturbance associated with the microcosm installation. Contrary to our hypothesis that earthworms would stabilize organic matter in soil aggregates, P. corethrurus decreased total soil C by 3% in the surface layer (0–15 cm), predominantly through a decrease in the C concentration of macroaggregates (>250 μm) and a corresponding depletion of C in coarse particulate organic matter occluded within macroaggregates. Earthworms also decreased bulk density by over 4%, but had no effect on aggregate size distribution. Within the two fertilized treatments, the QSMAS appeared to retain slightly more fertilizer derived N in smaller aggregate fractions (

Earthworms as agents for arsenic transport and transformation in roxarsone-impacted soil mesocosms: A µXANES and modeling study

Earthworms influence soil mixing during their feeding and burrowing activities by causing physical displacement and chemical transformations, potentially impacting the distribution and speciation of soil contaminants. This study investigates the effects of burrowing earthworms on arsenic speciation and mobility in soil mesocosms treated with roxarsone, an increasing anthropogenic source of arsenic used in the poultry industry as a feed supplement. Experiments were designed to test the hypothesis that earthworms and burrows provide means for biotransformation and redistribution of arsenic. Arsenic distribution was determined following earthworm bioturbation in artificial soil columns that were initially constructed with a contaminated layer of designated thickness and depth. The resulting depth profiles were used to indicate bioturbation rates by fitting them to a simple one-dimensional advection/diffusion model with a biodiffusivity that decreases with depth. Synchrotron X-ray methods reveal additional small-scale displacement of arsenic near the burrow and in the bulk soil. Microbeam X-ray Absorption Near Edge Structure spectra were collected to determine arsenic speciation. Arsenic initially introduced as roxarsone tended to be in a methylated form after 30 days. Within the earthworm tissue, arsenic–glutathione complexes were formed. Results are viewed in the context of poultry litter used as agricultural fertilizer. A decrease in tillage arising from soil conservation efforts allows earthworm populations to increase and burrows to become more permanent. This study suggests that (1) burrows serve as macropores allowing rapid transport of arsenic to greater depths during infiltration events; (2) bioturbation rates appear to be depth-dependent; and (3) earthworm soil mixing produces potentially mobile forms of arsenic that may become bioaccessible as arsenic is transported through the subsurface.

Vermicompost derived from different feedstocks as a plant growth medium

This study determined feedstock effects on earthworm populations and the quality of resulting vermicomposts produced from different types of feedstocks using different vermicomposting durations. Feedstock combinations (Kitchen Paper Waste (KPW), Kitchen Yard Waste (KYW), Cattle Manure Yard Waste (CMY)), three durations of vermicomposting (45, 68 or 90days), and two seed germination methods (with two concentrations of vermicompost) for radish, marigold and upland cress, served as the independent variables.The worms (Eisenia fetida) doubled their weight by day 68 in KPW and CMY vermicomposts and day 90 KPW vermicompost produced the greatest weight of worms. The direct seed germination method (seeding into soil or vermicompost–soil mixtures) indicated that KPW and KYW feedstocks decreased germination compared to the control, even in mature vermicompost. Seed germination was greater in the water extract method; however, most of the vermicompost extracts suppressed germination of the three seed species compared to the water controls. Vermicomposts from all three feedstocks increased leaf area and biomass compared to the control, especially in the 10% vermicompost:soil mix. Thus, seed germination and leaf area or plant biomass for these three species are contrasting vermicompost quality indicators.

Pathogen reduction in septic tank sludge through vermicomposting using Eisenia fetida

This study evaluated the potential of earthworms ( Eisenia fetida) to remove pathogens from the sludge from septic tanks. Three earthworm population densities, equivalent to 1, 2, and 2.5 kg m -2, were tested for pathogen removal from sludge. The experimental phase lasted 60 days, starting from the initial earthworm inoculation. After 60 days, it was found that earthworms reduced concentrations of fecal coliforms, Salmonella spp., and helminth ova to permissible levels (<1000 MPN/g, <3 MPN/g, and <1 viable ova/g on a dry weight basis, respectively) in accordance with Official Mexican Standard of environmental protection (NOM-004-SEMARNAT-2002) ( SEMARNAT, 2002). Thus, sludge treatment with earthworms generated Class A biosolids, useful for forest, agricultural, and soil improvement.

Earthworms, soil fertility and aggregate-associated soil organic matter dynamics in the Quesungual agroforestry system

Issues of food security, environmental degradation and global climate change underscore the need for the improved understanding of sustainable agricultural systems around the globe. The Quesungual slash-and-mulch agroforestry system (QSMAS) of western Honduras offers a promising alternative to traditional slash-and-burn (SB) agriculture for the mountainous tropical dry forest zones of Central America, but the overall influence of this system on soils is not fully understood. We examined earthworm populations, soil fertility and soil organic matter (SOM) dynamics under QSMAS and SB agriculture, with secondary forest (SF) as a reference. Both QSMAS and SB consisted of treatments with and without inorganic fertilizer (N–P–K) additions, resulting in five management treatments, each present on three replicate farms. Baseline soil samples (0–15 cm) were collected prior to forest clearing and establishment of QSMAS plots in 2003 and in SB and SF plots in 2005 to determine initial soil concentrations of C and N. Soils were sampled in 2006 and 2007 for bulk soil C and N and P availability, as well as for aggregate fractionation and determination of C and N within the different aggregate size fractions. Earthworm populations were assessed in July 2007. Earthworm numbers and biomass were higher under QSMAS than under SB (13.4 vs. 0.8 g fresh biomass m − 2 ; respectively). Significant interactions between cropping system and fertilization suggest that QSMAS increased the availability of added inorganic P, 3 times more under QSMAS than for SB. Comparisons with SF, indicated that both cropping systems resulted in a dramatic loss of C (average 5 g C kg − 1 soil) since treatment implementation, and that this loss was mainly associated with the disruption of C rich large macroaggregates (> 2000 µm). After taking into account baseline soil C differences between plots, no major differences in total SOM losses were found between QSMAS and SB management. However, earlier establishment of QSMAS plots suggests that the overall rate of C loss since treatment establishment was lower for QSMAS than for SB. Results from this study suggest that the Quesungual agroforestry system offers great potential to improve soil fertility and biological health in the region relative to traditional slash-and-burn agriculture.

Modelling the effects of bioturbation on the re‐distribution of137Cs in an undisturbed grassland soil

Under favourable conditions, soil ingestion by earthworm populations can be equivalent to approximately 5–10% of the topsoil mass per year. This suggests that for contaminants that are strongly bound to soil, earthworm ‘bioturbation’ may be a more important transport mechanism than water‐borne advection dispersion. It is therefore quite surprising that few modelling studies to date have explicitly considered the effects of biological processes on contaminant transport in soil. In this study, we present a general model that incorporates the effects of both ‘local’ and ‘non‐local’ biological mixing into the framework of the standard physical (advective‐dispersive) transport model. The model is tested against measurements of the redistribution of caesium‐137 (137Cs) derived from the Chernobyl accident, in a grassland soil during 21 years after fallout. Three model parameters related to biological transport were calibrated within ranges defined by measured data and literature information on earthworm biomasses and feeding rates. Other parameters such as decay half‐life and sorption constant were set to known or measured values. A physical advective‐dispersive transport model based on measured sorption strongly underestimated the downward displacement of137Cs. A dye‐tracing experiment suggested the occurrence of physical non‐equilibrium transport in soil macropores, but this was inadequate to explain the extent of the deep penetration of137Cs observed at the site. A simple bio‐diffusion model representing ‘local’ mixing worked reasonably well, but failed to reproduce the deep penetration of Cs as well as a dilution observed close to the soil surface. A comprehensive model including physical advective‐dispersive transport, and both ‘local’ and ‘non‐local’ mixing caused by the activities of both endogeic and anecic earthworms, gave an excellent match to the measured depth profiles of137Cs, with predictions mostly lying within confidence intervals for the means of measured data and model efficiencies exceeding 0.9 on all sampling occasions but the first.

Impact of Coffee Management Practices on Earthworm Populations in Puerto Rico

Abstract The conditions under which coffee is grown may affect its long-term sustainability through effects on soil fauna, including earthworms, which have a profound effect on abiotic and biotic properties and processes in natural and agricultural ecosystems. We examined differences in earthworm populations among sun (SUN) and shade (SHD) coffee and secondary forest (FOR) ecosystems, as well as soil order (Oxisols, Ultisols, Inceptisols) in western-central Puerto Rico. Ecosystem type significantly affected earthworm population density (individuals/m2), which followed the order: SUN (281) > SHD (125) = FOR (37). Earthworm biomass (g fresh weight/m2) was also significantly affected by ecosystem type, following the order: SUN (71) > SHD (34) = FOR (12). In general, neither earthworm biomass nor abundance was significantly related to litter quantity, litter composition or soil properties for any of the ecosystems studied. The absence of significant differences between SHD and FOR ecosystems suggests similari...

The characteristics of earthworm communities along vertically stratified transect of Velika Kapela Mountain grasslands (Croatia)

The spatial and temporal variability of earthworm populations is very high, both within and between differently managed types of land. Additionally, grassland ecosystem earthworm communities are reported as more heterogeneous and difficult to distinguish from one another in comparison to other types of ecosystems. The current study involves seven sites situated along the transect from the city of Ogulin on the continental slope to the Novi Vinodolski on the Mediterranean slope of the Velika Kapela Mountain. A plot of approximately 100 x 100 m in size was randomly selected for study. On each selected plot, seven random, seven transect, and 16 regular grid sampling points were chosen for earthworm sampling. A combination of hand sorting and expulsion by formalin was used for earthworm sampling. From all three sampling designs, transect had the lowest species number observed in all seven sites and regular grid sampling elicited the highest number of species in five sites. Two sites on the south-eastern slope of the Velika Kapela Mountain had the lowest species richness among all sites. The total number of species per site ranged from three to eleven. Aporrectodea rosea (Savigny, 1826) was the only species present at all seven sites, followed by Dendrobaena octaedra (Savigny, 1826) and Octolasion lacteum (Ör-ley, 1881) found on five sites. The use of various species richness estimators suggested that on several sites one or two species were lacking from the sampling.

The Role of Earthworms in Tropics with Emphasis on Indian Ecosystems

The paper highlights the research carried out by different scientists in India on aspects of earthworm population dynamics and species diversity, associated with other soil fauna and microflora. It also deals with the importance of earthworm activity on physicochemical properties of soil with reference to India and other tropical countries. Stress is laid on the earthworm plant association and importance of the secretions of earthworms as plant growth stimulators. Moreover, the earthworm species reported and being utilized for vermicomposting in India are discussed, since vermicomposting is the ultimate technology which renders for the improvement of soil fertility status and plant growth. Earthworms serve as indicators of soil status such as the level of contamination of pollutants: agrochemicals, heavy metals, toxic substances, and industrial effluents; human-induced activities: land-management practices and forest degradation. In all these fields there is lacuna with respect to contributions from India when compared to the available information from other tropical countries. There is lot of scope in the field of research on earthworms to unravel the importance of these major soil macrofauna from holistic ecological studies to the molecular level.

Endogeic and anecic earthworm abundance in six Midwestern cropping systems

Endogeic and juvenile anecic earthworm abundance was measured in soil samples and anecic populations were studied by counting midden numbers at the sites of two long-term cropping systems trials in South-central Wisconsin. The three grain and three forage systems at each site were designed to reflect a range of Midwestern USA production strategies. The primary objectives of this work were to determine if the abundance of endogeic or anecic earthworms varied among cropping systems or crop phases within a cropping system and were there specific management practices that impacted endogeic or anecic earthworm numbers. The earthworms present in the surface soil were: Aporrectodea tuberculata (Eisen), A. caliginosa (Savigny), A. trapezoides (Dugés); and juvenile Lumbricus terrestris (L.). True endogeic abundance was greatest in rotationally grazed pasture [188 m −2 at Arlington (ARL) and 299 m −2 at Elkhorn (ELK)], and smallest in conventional continuous corn (27 m −2 at ARL and 32 m −2 at ELK). The only type of anecic earthworm found was L. terrestris L. There was an average of 1.2 middens per adult anecic earthworm and the population of anecics was greatest in the no-till cash grain system (28 middens m −2 at ARL, 18 m −2 at ELK) and smallest in the conventional continuous corn system (3 middens m −2 at ARL, 1 m −2 at ELK). Earthworm numbers in individual crop phases within a cropping system were too variable from year-to-year to recommend using a single phase to characterize a whole cropping system. Indices for five management factors (tillage, manure inputs, solid stand, pesticide use, and crop diversity) were examined, and manure use and tillage were the most important impacting earthworm numbers across the range of cropping systems. Manure use was the most important management factor affecting endogeic earthworm numbers; but no-tillage was the most important for the juvenile and adult anecic groups and had a significantly positive influence on endogeic earthworm counts as well. The pesticides used, which were among the most commonly applied pesticides in the Midwestern USA, and increasing crop diversity did not have a significant effect on either the endogeic or anecic earthworm groups in this study. Consequently, designing cropping systems that reduce tillage and include manure with less regard to omitting pesticides or increasing crop diversity should enhance earthworm populations and probably improve sustainability.

Soil Invertebrates as Bio-indicators in a Natural Area Converted from Agricultural Use: The Case Study of Vallevecchia-Lugugnana in North-Eastern Italy

This work aims to develop a sampling methodology, based on soil invertebrates, to provide a reliable and easy-to-perform measure of environmental quality. Hand-sorting and pitfall-trapping were the main sampling systems adopted because they are quick and easy to use and do not require particular skills or tools. Both agroecosystems (organic and conventional) and seminatural environments (planted woods, hedgerows, flooded areas) have been monitored in a coastal lagoon area reclaimed to farmland in North Eastern Italy. Taxa at high hierarchical levels proved to be useful in separating different type of habitat, but were unable to provide information about the type of rural management. Carabidae (Coleoptera) seem particularly useful in studying agroecosystems: 23 species have been collected, mainly in the organic farm and in the hedgerow. The earthworm population was mainly affected by type of soil. In agroecosystems, cultivated fields had fewer individuals with respect to hedgerow, probably due to disturbance caused by soil management practices.

Vermicompost as a fertilizer for urban and peri-urban farms: Perceptions of farmers in Accra, Ghana

Vermicompost is considered a valuable organic fertilizer in many tropical regions, but has rarely been used in sub-Saharan Africa. A study in Accra, Ghana, assessed urban and peri-urban (UP) farmers’ fertilizer and pesticide use, knowledge of earthworms, fertilizer performance criteria, and attitudes toward vermicompost as a fertilizer. Twenty-six farmers involved in irrigated vegetable farming and three subsistence farmers were interviewed. Farmers were aware that earthworm activity was associated with soil fertility, and some associated insecticide applications to reduced earthworm populations. Farmers used the greenness of leaves, crop emergence, stand and yield as indicators of fertilizer performance. Farmers resisted making statements about vermicompost before testing it, and advised that its fertilizer value be tested during the dry season. Farmers involved in irrigated vegetable farming had insufficient space and time for on-farm vermicomposting, while subsistence farmers lacked a reliable access to water necessary for on-farm vermicomposting; but both types of farmers were interested in adopting vermicompost if it improved crop performance. Such lack of farm resources suggest that a commercial facility would be best suited to produce vermicompost from organic waste, which would then be sold to farmers.

Influence of driver ant swarm raids on earthworm prey densities in the Mount Kenya forest: implications for prey population dynamics and colony migrations

African driver ants are nomadic social mesopredators feeding on a highly diverse array of prey species at different trophic levels. Colonies of certain driver ant species have a biomass which can equal that of medium-sized mammalian carnivores and the ultimate cause of their nomadic life-style is thought to be local prey depletion. The impact of driver ant swarm raids is therefore expected to be strong but the degree to which they reduce prey populations has not been quantified and it is unknown whether these spectacular predators exert significant top-down effects. We examined the combined effect of driver ant (Dorylus molestus) and swarm-attending bird (Alethe poliocephala) predation on the population dynamics of earthworms, which constitute the ants’ main prey type in the montane forest of Mount Kenya. Pre-raid earthworm biomass densities in the soil layer down to a depth of 8 cm varied by a factor of 31. The immediate effect of swarm raids was a reduction in earthworm numbers in this layer, but 8 days later earthworm numbers had recovered to pre-raid levels. When earthworm biomass densities were compared, no significant effect of swarm raids was detected. The estimated proportion of earthworm prey biomass extracted from 0 to 8 cm layer by driver ants and birds together was about 2.2%. Although colony distribution was overdispersed as expected based on knowledge of D. molestus migratory behaviour, predation events were highly localized. Predation frequency was low (once every 62 days on average) and highly variable. These results indicate that earthworm prey is highly abundant but at the same time so difficult to harvest that swarm raids exert only a marginal influence on earthworm populations. Longer-term studies would be required to determine whether earthworm populations are limited by swarm raids. The small impacts of individual raids and rapid recovery of earthworm prey populations likely underlie the low frequency of migrations and short distances travelled by migrating colonies of D. molestus.

Habitat quality, conspecific density, and habitat pre-use affect the dispersal behaviour of two earthworm species, Aporrectodea icterica and Dendrobaena veneta, in a mesocosm experiment

Dispersal capacity is a life-history trait that may have profound consequences for earthworm populations: it influences population dynamics, species persistence and distribution and community structure. It also determines the level of gene flow between populations and affects processes such as local adaptation, speciation and the evolution of life-history traits. It may play a great role in soil functioning by determining the spatial distribution of ecosystem engineers such as earthworms. Dispersal is an evolutionary outcome of the behaviour in response to the ecological constraints of the species. Hence different dispersal behaviour is expected from the different ecological types of earthworms. Nevertheless the dispersal behaviour of earthworms has been little documented. In this work we test a series of basic mechanisms that are fundamental and complementary to understand earthworms dispersal behaviour. We focus on the dispersal triggered by environmental conditions, a fundamental process usually termed “conditional dependent dispersal”. We show experimentally in mesocosms that in one week: 1) earthworm dispersal can be triggered by low habitat quality, either through soil quality or the presence/absence of litter. 2) Earthworms can be subject to positive density dependent dispersal, that is the rate of dispersal increases when density increases; and 3) earthworm dispersal can be reduced by the pre-use of the soil by conspecific individuals that are no longer present. Our results suggest that earthworms may be more mobile than expected from previous estimations, and that they present high capacities of habitat selection. In the light of our findings we elaborate a behavioural scenario of earthworm foraging, and propose several priority working directions.

A feeding induced switch from a variable to a homogenous state of the earthworm gut microbiota within a host population.

BackgroundThe distribution pattern of the earthworm gut microbiota at the host population level is of fundamental importance to understand host-microbiota interactions. Our current understanding of these interactions is very limited. Since feeding represents a main perturbation of the gut microbiota, we determined the effect of a single dose of feed on the microbiota associated with an earthworm population in a simulated microenvironment.MethodologyEarthworms were sampled 0, 1 and 7 days after feeding. We determined the overall composition of the earthworm-associated microbiota by 16S rRNA gene cloning and sequencing. Based on the 16S rRNA gene data we constructed quantitative PCR's (Q-PCR) for the seven most dominating bacterial groups.Principal FindingsQ-PCR revealed low density and highly variable microbiota among the earthworms before feeding, while a high-density homologous microbiota resulted from feeding. We found that the microbiota 1 day after feeding was more equal to the microbiota after 7 days than before feeding. Furthermore, we found that the gut microbiota was very distinct from that of the bedding and the feed.SignificanceThe homogenous population response represents fundamental new knowledge about earthworm gut associated bacteria.