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The impact of pest management strategies on the soil biota is crucial since it includes a lot of recognized beneficial animals. Commercial orchards are precisely managed crops on which large amounts of pesticides are used. We aimed to provide a clear understanding of the response of ground beetles communities to such strategies. Field sampling was carried out in three seasons in 15 commercial orchards. We studied ground beetle communities through their activity-density, and their structural and functional diversity. We found activity-density to be solely influenced by season and species richness by orchard management but only in summer. Differences in orchard management selected individuals on the basis of their morphology (in relation with their stature, walk, flight and nutrition) and their ecological preferences (food and habitat diversity). Our results illustrate the value of trait-based approaches in depicting orchard management effects on the within-year dynamics of ground beetles, when combined with taxonomic approaches. (C) 2014 Elsevier B.V. All rights reserved.

[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 (<5 m), while soil physico-chemical characteristics showed a clumped spatial distribution. Contrary to previous results reported for the nearby savanna, a significant spatial association was found for two competing endogeic species Andiodrilus sp. and Glossodrilus sp. in the GF. Semi-variograms of soil environmental factors were adjusted to model families most commonly used (spherical and linear), and correlograms for earthworms showed significant positive and negative spatial autocorrelation for lag distances <15 m and >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 influe

Soil ecosystem engineers such as termites and ants are able to modify physico-chemically the surrounding environment through the production of biogenic structures, thus affecting the availability of trophic and spatial resources for other organisms. The aim of this study was to assess the concentrations of Corg, NH4+ and NO3− in the biogenic structures produced by a soil-feeding termite (Spinitermes sp.; Termitinae) and a fungus-grower ant species (Atta laevigata; Myrmicinae; tribe Attini) and the surrounding soil in the Colombian “Llanos”. We tested the hypothesis that higher concentrations occur in the biogenic structures compared to control soil and that deposition of new building material at the top of the biogenic structures also increases nutrient concentrations. Sampling was conducted along a transect, at regular intervals proportional to the size of the biogenic structure. Average Corg and NH4+ concentrations were significantly higher in termite mounds than in ant nests and the control soil, whereas NO3− concentrations were similar. For both types of biogenic structures, the highest difference in nutrient concentrations was found between the top centre of the biogenic structure and the control soil, but significant differences were only reported for Spinitermes mounds and the control soil. No significant effect of land use on nutrient concentrations in the biogenic structures produced by either species was observed. We conclude that the activities of soil ecosystem engineers contribute to the variability of nutrient concentrations through the formation of biogenic structures.

[EN] Pit digging and manually revising soil blocks is a frequently used method used for field studies of earthworm communities. The aim of this study was to compare the efficiency of hand-sorting (HS) to extract small earthworms, ca. 0.2 g, and the usefulness in studies of population dynamics and cohort analysis. Many earthworms are not recovered when revising manually the soil. Factors include soil characteristics, i.e. moisture, texture, etc. and also a human factor, which is more relevant if the study is conducted in the long-term. We used data collected in a field study of earthworm communities during 2 years in the savannas of Colombia. Small soil blocks (20 × 20 × 20 cm) were dug out in order to collect the smallest earthworms by washing-sieving (WS) and compare the results with the standard HS of large monoliths (100 × 100 × 50 cm). In fact, this methodology has rarely been addressed in earthworm population field studies. Our results showed that HS efficiency varied owing to the species and ranged from 31.4% up to 100% in the savanna and from 44% to 80% in the pasture, for two small species, i.e Aymara n. sp. (epigeic) and Ocnerodrilidae sp. (endogeic). In the case of the Glossodrilus n. sp. (endogeic) these values were similar, i.e. 51.7% and 58.1%, in the savanna and pasture, respectively. We also used frequency tables to calculate the average efficiency of HS 1 m2 soil cores for each weight class in each species in order to obtain a population density correction factor. This allowed us to make corrections in earthworm density in the histograms for population dynamics analysis. We conclude that this method should be the modus operandi in long-term earthworm demography studies.

The spatial distribution of soil invertebrates is aggregated with high-density patches alternating with low-density zones. A high degree of spatio-temporal organization generally exists with identified patches of specific species assemblages, in which species coexist according to assembly rules related to competitive mechanisms for spatial and trophic resources occur. However, these issues have seldom been addressed. The spatio-temporal structure of a native earthworm community in a natural savanna and a grass–legume pasture in the Colombian “Llanos” was studied during a 2-year-period. A spatially explicit sampling design (regular grid) was used to discern the distribution pattern of species assemblages in both systems. Earthworms were collected from small soil pits at three different sampling dates. Data collected from 1 m2 soil monoliths were also used in the present study. Data were analyzed with the partial triadic analysis (PTA) and correlograms, while niche overlap was computed with the Pianka index. The PTA and correlogram analysis revealed that earthworm communities displayed a similar stable spatial structure in both systems during the 2-year study period. An alternation of population patches where different species' assemblages dominated was common to all sampling dates. The medium-sized Andiodrilus sp. and Glossodrilus sp. exhibited a clear spatial opposition in natural savanna and the grass–legume pasture for the duration of the study. The Pianka index showed a high degree of niche overlapping in several dimensions (vertical distribution, seasonality of population density) between both species. The inclusion of space-time data analysis tools as the PTA and the use of classical ecological indices (Pianka) in soil ecology studies may improve our knowledge of earthworm assemblages' dynamics.

By definition ‘ecosystem engineers’ are those organisms capable to modify physically the environment by producing ‘biogenic’ structures (BS). Large macroinvertebrates like termites, earthworms and ants produce BS with distinguishable physico-chemical properties. We measured total Corg, View the MathML source and View the MathML source contents in the BS produced by two species of Neotropical termites (subfamily Nasutermitinae) in a gallery forest (GF) of the Eastern Plains of Colombia. We sampled from the top of the BS to the edge at proportional distances, i.e. 20–100% for the largest BS in the soil surface and 50–100% for the smallest arboricole BS. Control soil was sampled 1 m apart from the BS. Values of total Corg were high in the BS produced by Nasutitermes sp1 (epigeic mound), while a high N mineralization process was observed in the same BS and in the Nasutitermes sp2 arboreal nest. The role of these two ecosystem engineers in nutrient cycling is discussed.

Martiodrilus n. sp. (Oligochaeta, Glossoscolecidae) is a large native earthworm from the natural savannas of the eastern plains of Colombia. The description of the main biological, ecological and functional attributes of this species in a natural savanna and several introduced pastures at the Carimagua Research Station (320 km east from Villavicencio) was the main objective in this study. Density and biomass of this species were significantly much higher in the introduced pastures compared with the savanna (ANOVA, P<0.01). Evidence of vertical migration during the year was observed, while it is active in the topsoil during the beginning of the rainy season, it enters in a true diapause to withstand adverse environmental conditions before the onset of the dry period, being adults the last to enter into this phase (after reproduction period). Martiodrilus n. sp. seemed to select food substrates with high organic contents since casts produced in the two systems had significantly higher total C and total N contents than the bulk soil. Besides, C content also increased significantly during ageing of casts (+100%), possibly because of CO2 fixation processes, accumulation of dead roots and/or macrofaunal activities. The effects of earthworm activities on soil and cast seed banks were revealed in another experiment. The composition of the above standing vegetation was relatively closer to that of the cast seed bank than that of the soil seed bank. The results obtained in this study support the general knowledge of how earthworms can affect soil fertility and plant growth. Martiodrilus n. sp., through the production of casts affects the availability and nature of both the spatial and trophic resource in soil. This species certainly belongs to the functional group of “ecosystem engineers”, as it affects the availability of some resources for other organisms through the production of physical biostructures. The next step in research should be directed now to test whether Marti

The objective of this study was to assess the effect of a native anecic species on phosphorus availability in an Oxisol characterised by a low chemical fertility. Experiments were carried out at Carimagua research station in a representative site of the isohyperthermic savannas on the Colombian Orinoco basin. One field study and two laboratory/incubation studies were performed in a natural herbaceous savanna and a Brachiaria decumbens and Pueraria phaseoloides pasture. In the laboratory, experiment pots were prepared containing soil collected from the respective field paddock's topsoil. Total P content was higher in earthworm casts than in the surrounding soil in field samples, 50% in native savanna soil and more than 100% in pasture soil. In casts produced under laboratory conditions this increase was relatively low (10–20%). Under field conditions, almost without exception, all P fractions were increased in casts relative to the original soil (corresponding to the increase in total P content), being relatively greater in the labile inorganic P fractions. In addition, samples from the natural savanna showed that pH of casts was higher (5.2) than that of soil (4.6) in both field and laboratory samples. Except in the native savanna under field conditions, the phosphatase activity was reduced in casts by 16.7 to 44%. From our results we conclude that earthworms in the field incorporate P from litter or other organic sources (i.e. undecomposed plant and root material, earthworm faeces) which is not normally measured in the analysis of bulk soil.

[EN] An ecological classification based on a set of morphological characters may be used to describe earthworm functions in soil. However these relationships have been seldom verified. Gizzards of the earthworm Martiodrilus carimaguensis (Glossoscolecidae) were studied to find out if its anecic morphology was in agreement with its diet (shallow litter remains and deep organo-mineral material). By direct observation of 13 adults’ gizzard contents with a dissecting and a phase contrast microscope, the volumetric percentage of plant fragments, roots, amorphous organic matter and mineral particles reached respectively 63, 5, 6.5 and 30 % v/v. Eighty percent of plant fragments were microscopic, and mostly incorporated into the organo-mineral earthworm casts well preserved in the gizzard. Coprophagy and rhizophagy were the dominant feature of M. carimaguensis diet. Yet, the casts produced revealed a high variability in its diet, what could be related to transitional adoption of a typical anecic diet during some periods., [FR] La classification écologique des vers de terre basée sur des caractères morphologiques permet de décrire leur fonction dans le sol. Cependant ces relations ont rarement été validées. Les gésiers du ver de terre Martiodrilus carimaguensis ont été étudiés pour vérifier que sa morphologie d’anécique l’amenait bien à consommer de la litière mélangée au sol superficiel. Les pourcentages volumiques des fragments végétaux, des racines, de la matière organique amorphe et des minéraux du contenu du gésier de 13 individus adultes, déterminés par l’observation directe à la loupe et au microscope, sont respectivement de 63, 5, 6,5 et 30 % v/v. Quatre-vingt pourcent des fragments végétaux sont microscopiques et incorporés au sein de déjections de vers de terre. La coprophagie et la rhizophagie sont les comportements alimentaires dominants de M. carimaguensis. Toutefois ses turricules attestent d’une variabilité de son alimentation qui pourrait résulter de l’adoption transitoire d’un régime d’anécique typique.

Aestivation is a period of inactivity included within the life cycles of many soil organisms. Due to physiological, genetic and environmental heterogeneity, earthworm aestivation may take on different forms. In this paper we used the term aestivation to refer to the inactivity of populations at any time of the year. Several strategies found in some tropical earthworm species are given in this article. The results were obtained in detailed studies of earthworm communities conducted in savannas of Colombia and Mexico, several Mexican pastures and some Miombo-derived agroecosystems in Tanzania. Although all species built aestivation chambers in which they coiled up at certain periods of the year, different patterns of aestivation were found: two Neotropical species were found inside a plastered mucus sphere while two other species did not form any mucus sphere but layered the end of the gallery with several faecal blocks, and one African species created an aestivation chamber with large sand grains that adhered to the earthworm, preventing it from touching the surface of the chamber's walls. A detailed description and drawings of the aestivation chambers of five earthworm species are given plus a complete analysis of the mechanistic processes that determine this behavioural pattern for one anecic species from Colombia. The onset of aestivation differed in adults and juveniles for two glossoscolecid tropical species, i.e. Glossodrilus n. sp. and Martiodrilus carimaguensis, a native anecic earthworm from the tropical lowlands of Colombia which undergoes diapause by burrowing deep into the soil during late rainy season, while immature individuals enter into this phase four months earlier. Relationships between the aestivation period and the addition of new segments in earthworms have been established by several authors. In this study there was no relationship for the only species studied in more detail.

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.