Vertical distribution of earthworms in grassland soils of the Colombian Llanos

The vertical distribution of native earthworm species from natural and disturbed savannas in the Oxisols of the Colombian Llanos was assessed in a native savanna and in a 17-year-old grazed grass-legume pasture during a period of 17 months. Different patterns of vertical stratification were observed for all species with a strong migration of populations to deeper layers in the dry season. The correlation between the size of the earthworms and the average depth at which they were found was not significant (P>0.05), despite the fact that bigger species are located deeper in the soil. The living habits and adaptive strategies of the smallest species, Ocnerodrilidae n. sp., found in both ecosystems studied are responsible for this pattern. This endogeic species is associated with organic pools generated by an anecic species and further studies should assess the role of this species in ecosystem functioning. Mature worms of one anecic species were located deeper than immature ones in the soil (P<0.01). Soil moisture had an important effect on the vertical distribution of earthworms, although differences between immature and mature worms of the anecic Martiodrilus carimaguensis are likely to be of biotic origin. New data on the biology and ecology of these Neotropical species are shown.This work was carried out within a research grant of the Macrofauna project (EC - STD2). We want to thank Professor Patrick Lavelle (IRD, France), and Drs. Richard J Thomas and Myles J Fisher (International Center for Tropical Agriculture, CIAT, Colombia) for their encouragement and enthusiasm to study the role of earthworms in the savannas and man-made pastures of Carimagua, in the Colombian “Llanos”. The first author would like to thank Jean Pierre Rossi (IRD, France) and two anonymous referees for helpful comments and their criticism on a first version draft of this paper.Peer reviewe

Population dynamics and adaptive strategies of Martiodrilus carimaguensis (Oligochaeta, Glossoscolecidae), a native species from the well-drained savannas of Colombia

23 páginas, 5 figuras, 2 tablas.Martiodrilus carimaguensis (Oligochaeta, Glossoscolecidae) is a large, anecic native earthworm species which was found in natural and disturbed savannas in the Oxisols of the Colombian Llanos. Its population dynamics were studied in a native savanna, and in a 17 years old grazed grass-legume pasture where density and biomass were higher. Monthly cast deposition on the soil surface in the improved pasture was 38.4×103 fresh casts ha−1, eleven times more than in the native savanna. A strong relationship was found between numbers of M. carimaguensis and numbers of fresh surface casts. Different patterns of adaptation to the dry season were observed for adults and juveniles. Adults are active for eight months whereas juveniles enter diapause 3–4 months earlier. The vertical distribution pattern of the earthworm population also shows marked seasonal changes.This work is funded by a research grant from the Macrofauna project (STD3 EC Program) for which we are greatly indebted. We also wish to thank CIAT (International Center for Tropical Agriculture), especially the Tropical Lowlands Program for human and technical support, and for scientific discussions on this study. Our deepest gratitude is expressed to all the people at Carimagua station, and especially to field workers, for their invaluable help.Peer reviewe

Diversity of mantids (Dictyoptera: Mantodea) of Sangha-Mbaere Region, Central African Republic, with some ecological data and DNA barcoding

This study aims at assessing mantid diversity and community structure in a part of the territory of the Sangha Tri-National UNESCO World Heritage Site in the Central African Republic (CAR), including the special forest reserve of Dzanga-Sangha, the Dzanga-Ndoki National Park. The study area is located in the biome of the dense tropical rainforest of the Congo Basin, the second largest area of tropical forest behind the Amazon basin, and one of the last regions on earth where pristine forest ecosystems persist. Between 1984 and 2012, eight collecting campaigns were conducted by P. Annoyer, M. Loubes and S. Danflous, with the aim of documenting invertebrate diversity in this remote and poorly studied area. Mantids were collected in different habitats and microhabitats using four harvesting techniques: visual hunting (threshing, mowing), active search in the trees, autonomous UV collecting (Remote Canopy Trap) and classical light trapping with mercury light. Community patterns were assessed using rarefaction curves and diversity estimators (ACE). Specimens (n = 25) were also found at the National Museum of Natural History (MNHN) of Paris. Seventy-one species of Mantodea are recorded from Sangha-Mbaere Region in the CAR from 1232 specimens. This is the first synthesis published about Mantodea in CAR. Some new species are present in the genera Cataspilota, Galepsus and Chlidonoptera. Taxonomic revisions of these genera are in progress. Some genera need global revision like Plistospilota, Miomantis, Entella, and Galepsus. This type of work is the first on the mantids in Central Africa since the various inventories carried out in the sixties and seventies, which were mainly based on lists of species. The contribution of data on ecology and biogeography is a novelty

Short-range spatial variability of soil physico-chemical variables related to earthworm clustering in a neotropical gallery forest

41 páginas, 6 tablas, 2 figuras[EN] In this study, we investigated the spatial distribution of an earthworm community together with the heterogeneity of selected soil properties in a gallery forest (GF) of the Colombian “Llanos”. We performed fine-scale spatial variability by intensively sampling 100 points distributed in the nodes of a regular grid with 5 m inter-sample distance. Non-parametric statistics were used and included SADIE analysis and partial Mantel test, in addition to geostatistics (semi-variograms) and correlogram computation. Our results indicated that the spatial distribution of earthworms was characterized by areas of presence (patches) and absence (gaps), although the general pattern was random at the scale of this study (30 m, respectively. Partial Mantel test revealed specific significant relationships between soil variables and some species. The earthworm community of the GF displayed a random structure in a spatially clumped soil environment, and our results suggested that spatial distribution observed for some species could be the result of preferential selection of soil environmental factors. In other words, soil heterogeneity contributed to the formation of population patches for some earthworm species. The variability of suitable sites (resource availability patchiness) exerted an influence in the spatial distribution of earthworms at the scale used in this study, and we identified the spatial scale at which both environmental heterogeneity could influence and express earthworm impact on soil properties.Local names for tree species of the gallery forest are those specifically used in the Carimagua region, and field assistants Jose García, Salvador Rojas and Guillermo Murcia are deeply appreciated for their help in field sampling and sharing their knowledge. CIAT and IRD provided financial and logistic support during field work. We would like to thank research assistant Jaumer Ricaute for root analysis at CIAT lab. Thanks are extended to Jean-Pierre Rossi (INRA) for fruitful discussions on spatial statistics tools, and Michael S. Rosenberg (Arizona State University) for availability and permission to use PASSaGE software. Finally, the useful comments of two anonymous referees and assigned editor are greatly acknowledged.Peer reviewe

Can We Predict How Earthworm Effects on Plant Growth Vary with Soil Properties?

Earthworms are usually assumed to enhance plant growth through different mechanisms which are now clearly identified. It is however difficult to determine their relative importance, and to predict a priori the strength and direction of the effects of a given earthworm species on a given plant. Soil properties are likely to be very influential in determining plant responses to earthworm activities. They are likely to change the relative strength of the various mechanisms involved in plant-earthworm interactions. In this paper, we review the different rationales used to explain changes in earthworm effect due to soil type. Then, we systematically discuss the effect of main soil characteristics (soil texture, OM, and nutrient contents) on the different mechanisms allowing earthworm to influence plant growth. Finally, we identify the main shortcomings in our knowledge and point out the new experimental and meta-analytical approaches that need to be developed. An example of such a meta-analysis is given and means to go further are suggested. The result highlights a strong positive effect size in sandy soil and a weakly negative effect in clayey soil

Numerical continuation methods: a perspective

AbstractIn this historical perspective the principal numerical approaches to continuation methods are outlined in the framework of the mathematical sources that contributed to their development, notably homotopy and degree theory, simplicial complexes and mappings, submanifolds defined by submersions, and singularity and foldpoint theory

Systematic revision of Gatesona (Crassiclitellata, Lumbricidae), an endemic earthworm genus from the Massif Central(France)

The Massif Central in France could potentially harbor numerous ancient endemic lineages owing to its long history of continuous geological stability. Several endemic earthworm species inhabit the area, with Allolobophora (Gatesona) chaetophora, Helodrilus (Acystodrilus) and Avelona ligra showing hints of a common evolutionary origin. However, the phylogenetic relationships and taxonomic status of the species remain to be studied through integrative molecular and morphological methods. To this end, eight species including most of the known species and subspecies of All. (Gatesona), Helodrilus (Acystodrilus) musicus, and Avelona ligra were sequenced for a set of five molecular markers. The species were grouped on the basis of the molecular findings in a phylogenetic framework. All. (Gatesona) was included within the same clade as Helodrilus (Acystodrilus) and Avelona, separated from Allolobophora sensu stricto, supporting its status as a good genus. Branch lengths and average pairwise genetic distances suggested the subspecies of All. (Gatesona) chaetophora examined should be considered species-level taxa. Thus, a generic diagnosis for Gatesona stat. nov. is provided, along with redescriptions of Gatesona chaetophora comb. nov., Gatesona rutena comb. nov. stat. nov., Gatesona lablacherensis comb. nov. stat. nov. and Gatesona serninensis comb. nov. stat. nov. The study findings highlight the need for further sampling of earthworm diversity in the Massif Central (and Southern France), in addition to an increased focus on the Eastern European species of Helodrilus

Earthworm management in tropical agroecosystems

Data of 145 and 69 earthworm communities from managed and natural ecosystems, respectively, of four continents and 15 tropical countries were analysed. The aim of the study was to separate the influence of phylogenetic, environmental and agricultural factors on the structure of earthworm communities in agroecosystems, and to evaluate their relative importance in the whole soil macrofauna community. Earthworms comprise 40-90% of macrofaunal biomass in most ecosystems except for annually cropped systems. Three major conclusions were drawn from the analysis of community structure (regional analysis) : (i) crops were, independently of region, characterized by a loss of native species and by the dominance of exotic endogeics ; (ii) pastures were highly heterogenous in terms of native or exotic species dominance ; (iii) native species survived better in management ecosystems of India and Africa than in Mexico-Central America. Local analysis in selected countries indicated that, as a general rule, the intensity of agricultural practices is negatively correlated with the amount of native species and the total abundance and biomass of earthworms ; the only exception was found in the conversion of savannas to pastures, in Colombian llanos. (Résumé d'auteur