Abstract: Soil disturbances that exert strong impacts on biota and their resources are also expected to induce
changes in the web of interactions among soil variables. The objective of this paper was to explore
the hypothesis that during the first years after the conversion from conventional to organic farming
gradual changes occur in the correlations among the nematode, microbial and nutrient flow components,
resulting in increased complexity of the soil system.
To test this hypothesis, we used network analysis techniques to analyze data from conventional (Conv)
and organic asparagus cultivations, as well as from the adjacent hedgerows (Hedg). Organic cultivations
were managed organically for 2, 3 and 5 years (Org-2, Org-3, Org-5), representing thus steps along a
gradient that corresponds to the duration of organic farming.
The estimated network cohesion and centrality, as well as the key player metrics, showed that the
correlation network of the newest organic systems, and mostly that of Org-3, was disorganized compared
with that of Conv. This trend was reversed, and a complex and more cohesive network was formed in Org-
5. In addition, by employing QAP techniques and Spearman rank correlation coefficients, inter-network
correlations were estimated and similarities were found between the correlation network from Org-2
and that of Org-3. The structure of the latter was correlated with that from Org-5.
Our results indicated that the conversion of a conventional system to organic induces a disturbance into
the soil system routine, probably launching secondary successional changes in the interactions among
soil components. These changes seem to involve the gradual destruction of existing interactions leading
to the disorganization of the correlation network and the reconstruction of a more complicated one after
3–5 years.
Abstract: Anthropogenic pressures that involve different kinds of inflows (chemical vs organic) to soils are likely to induce different responses of individual soil components as well as to affect the web of interactions between them. The aim of this paper was to explore whether chemical or organic disinfection constitute two different types of disturbance, regarding both their severity on individual soil components and the structural changes they induce on the network of interactions among soil biochemical variables and nematode functional guilds. Network analysis, a novel approach in the context of soil ecology, was used to explore these interactions.
Different plots within a field cultivated conventionally with Phaseolus vulgaris for many years were disinfected either with metham sodium or with a mixture of plant-based alternatives (neem and essential oils). Control plots receiving no disinfectants were also included in our study. One month after the treatments were applied, we estimated microbial C and N, activities of asparaginase, glutaminase, urease and phosphatase, organic C and N, inorganic N and P as well as the functional diversity of nematodes.
Chemical disinfection had a direct lethal effect on all nematodes, while the effect on the microbial community was less obvious, implying that at the time of sampling, microbial populations, especially bacterial ones had started to recover from disturbance. Urease and phosphatase activities were inhibited, which may partly be responsible for the reduced amounts of inorganic N and P. Organic disinfectants reduced microbial populations, mainly the fungal ones, but they did not inhibit enzyme activities. The availability of N and P increased and nematode abundance was not affected significantly.
The results demonstrate the usefulness of network analysis in providing insight into the structure and robustness of the soil network and its response to disturbance. Despite the pronounced reduction in nematode numbers due to chemical disinfection, the importance of nematode guilds within the interaction network was amplified and a more compact network was formed. On the other hand, interactions within organic plots were found to be primarily dictated by soil biochemistry. Finally, the analysis showed that both types of disinfection increased the vulnerability of the interaction network and this was more pronounced in chemically treated plots.
Abstract: The aim of this study was (a) to explore long-term responses of soil nematodes to the conversion from conventional to organic cultivation and (b) to differentiate them from the short-term responses to seasonal agricultural practices. Nematode communities were studied in terms of trophic and generic structure, life strategy and diversity, in asparagus cultivations along a gradient from conventional to organic under conversion (1 and 2 years), and certified organic (4 and 5 years). Samplings throughout the year were conducted with respect to seasonal agricultural practices. Changing management regime from conventional to organic cultivation seemed to initiate successional long-term changes in nematode communities, such as the gradual decline of phytoparasites in favour of bacterivores and fungivores, the gradual decrease of PPI, the increase of diversity. Alterations in the generic structure of the community were also revealed, driven mostly by the opposite trends of changes in abundance of Helicotylenchus vs. Heterocephalobus. Seasonal agricultural practices appeared to induce short-term responses of functional guilds of low colonizer-persister values (c-p I and 2) mostly, and were reflected in nematode indices, such as Maturity Index, Plant Parasitic Index, Enrichment Index, Channel Index but not Structure Index. Nematode responses at the generic level to seasonal agricultural practices seemed less intense than the ones imposed by changing management regime, and in the case of conventional cultivation they were almost entirely masked.
Abstract: In this study we describe and compare nematode communities in terms of trophic and generic structure, life strategy and diversity, in soils under asparagus cultivation managed conventionally and organically. Natural hedgerows bordering cultivations were also studied as reference systems. The bacterivore/fungivore group, accounted for 80% of total nematode abundance under organic cultivation, whilst phytoparasites increased in abundance in conventional plots resulting in higher plant parasitic index (PPI). The low generic diversity and strong dominance pattern observed under conventional cultivation indicated a stressed soil environment. In the organically managed system diversity was almost as high as in natural hedgerows, with nematode numbers evenly distributed among genera. However, in hedgerows intermediate abundances of bacterial, fungal and plant feeders were recorded, and the maturity index (MI) and PPI were higher than those of the organically managed system, indicating that organic farming resulted in a more vigorous, pre-mature and probably more productive soil rather than in a more 'natural' one. The different impacts of organic and mineral fertilizers are discussed.
Abstract: In this work we described and compared the community organization patterns of Coleoptera in various sites of the Dadia forest reserve, including different types of vegetation and management practices (grazing, cultivation, afforestation). Sampling was carried out every two months for a year, by means of pitfall traps. For studying diversity and community structure, we used Renyi's parametric index of diversity and fitted the geometric series model on rank/abundance data. In order to study the changes of species composition, we used the Indicator Value method (IndVal), after a tree clustering of our sampling sites. According to our results, although the three management practices increased the diversity of epiedaphic Coleoptera, their effects on the community organization patterns were different. Grazing did not affect the species composition of the communities but altered the community structure. The communities in the ungrazed forests were over-dominated by one species, while those of the grazed sites were hierarchically structured. On the other hand, the main effect of cultivation on the coleopteran communities was a profound change in species composition. The cultivated site was dominated by characteristic species that were almost absent from all other sites. Afforestation caused intermediate changes in both community structure and composition. Finally, although certain species of Coleoptera seemed to be good indices for assessing human impacts on natural environment, the study of changes in the community organization patterns is even more appropriate.
Abstract: This paper refers to the effects of large-scale seasonal fluctuations as well as experimentally induced small-scale variations of soil temperature and moisture on the structural and functional characteristics of a soil nematode community from a Greek Mediterranean grassland. Two levels of soil temperature, with a mean difference of 1.4 degrees C, and two levels of moisture (2.3 % difference in water content) were created. The experiment lasted for a six-month period (from July to December). All nematode community parameters vary significantly with season, with the exception of the environmental constant (C-env), which reflects the intensity of competition. The Maturity Index (MI) is affected only by seasonally fluctuating soil conditions, while the Plant Parasite Index (PPI) is affected only by the small-scale differences in soil temperature and moisture. The high value (1.48) of bacterivorous to fungivorous ratio (B/F) indicates mainly bacterial mediated decomposition, resulting in good soil fertility. The B/F ratio is affected both by large and small-scale changes in soil conditions. Diversity and richness show dependence on seasonal variations as well as on small changes in temperature, while no effect of moisture is recorded. The correlations between nematode community parameters, microflora parameters and soil nitrogen pools show independence of nematode parameters from soil N-pools (N-organic and N-inorganic) and parameters relating to microflora, as well as strong dependence on microbially-bounded nitrogen.
Abstract: The null hypothesis of this paper is that survival of arthropods under the severe Mediterranean conditions involves specific combinations of conservative and conformist traits. To test this hypothesis a modeling approach employing a Leslie-type matrix model and a fuzzy systems technique for parameter estimation is developed and applied to a model species. The general conclusion is that the results of this paper add support to the null hypothesis, whereas specific conclusions are as follows: 1) matrix models merging demographic and physiological parameters are suitable tools for the simulation of population dynamics of arthropods and further for the discussion of the interplay among life history traits; 2) employing linguistic instead of arithmetic variables, fuzzy approaches allow for the formalization of incomplete and/or missing data exploiting expertise concerning related species; 3) in general, population dynamics of arthropods follow the seasonality of the Mediterranean climate; 4) the basic mechanism underlying skewing phenologies and stochastic equilibrium is identified with the type of temperature dependence of arthropod metabolic activity; 5) under optimal conditions an exponential trend is superimposed on seasonal population dynamics; 6) more realistic conditions involving large-scale random oscillation in temperature in autumn and spring coupled with small-scale temperature oscillation in summer and winter result in stochastic equilibrium; 7) moderate contamination of soil and medium-scale oscillation in temperature result in stable temporal patterns; 8) a sensitivity analysis shows disproportional effect of different demographic parameters on population growth rate. Fecundity of young and middle-aged adults is most important for the rate of population growth, whereas elder animals are considered an important pool for maintenance of the population.
Abstract: This paper describes the effects of large-scale seasonal fluctuations as well as experimentally induced small-scale variations of soil temperature and moisture on the community of bacterivorous nematodes and the activity of soil bacteria from a Greek Mediterranean grassland. Our experiment spanned a 6-month period (July-December 1996), during which artificially created changes in temperature (1.4degreesC) and moisture content of the soil (2.3%) were superimposed on seasonal variations of these variables. Functional diversity of soil bacteria was assessed using Biolog GN-plates. Bacterial diversity, richness and evenness as well as the mean oxidation of almost all Biolog substrate groups, were affected significantly by the seasonal fluctuations of soil temperature and moisture, and declined linearly from July to December. The substrates responsible for the differences in monthly soil samples were mainly carbohydrates and carboxylic acids. The small-scale experimental changes in temperature and moisture affected oxidation of only four out of the eight substrate groups. The effect of seasonality was also obvious on the diversity, evenness, richness and total density of soil bacterivorous nematodes, which exhibited higher values during the period September-October. The effect of experimental temperature and moisture modifications varied between the different nematode taxa. Acrobeles, Chiloplacus and Cephalobus responded significantly to small-scale temperature changes, while the responses of the other taxa, if any, were more complicated, depending on the interactive effect of both soil temperature and moisture. In any case, the experimental modifications of moisture alone did not induce significant changes in the structure of the nematode community. After comparing the community parameters of bacteria and bacterivorous nematodes, we conclude that there was no synchronised response between nematodes and their food resources. (C) 2003 Elsevier B.V. All rights reserved.
Abstract: The Strymonikos project was part of the EU Integrated Coastal Zone Management (ICZM) Demonstration Programme aiming at promoting concerted actions for the sustainable development of the Strymonikos coastal zone. There were three main problems that we had to face: (a) lack of data regarding the natural environment and human impacts, (b) complex jurisdictions of the bodies involved in the management of the area, and (c) the insufficient level of environmental awareness. These problems were tackled mainly through the following actions: (a) description and monitoring of the project zone, a necessary step for management planning, (b) establishment of a coordination scheme, a step toward integrated management, (c) establishment of an Information Centre for coastal zones in the Strymonikos area, a step to support environmental awareness and to promote cooperation. This step-by-step process and the problems that we have encountered are discussed.
Abstract: In this paper we describe and compare the oribatid distribution patterns at two scales: a regional scale corresponding to an altitudinal gradient and a local one created by the variation of vegetation cover. Distribution patterns at the local scale are assessed by sampling under the canopy of the Juniperus sp. shrubs, which are scattered. all along the altitudinal gradient, and at the adjacent grass-covered openings. Our results showed that the two scale effects are not equally important in shaping the oribatid communities. Altitude per se does not induce clear distribution patterns, acting mostly indirectly through the effect on the formation of local vegetation. In contrast, profound differences in the structure of oribatid communities are imposed by the local scale effect, which consists of strong microclimatic fluctuations in the exposed grassy sites and litter accumulation in the sheltered shrubby sites. Oribatids respond to the two scale effects, forming separate communities with distinct characteristics. The temporal heterogeneity of the exposed habitats at all altitudes leads to a temporal separation of oribatid niches and to a seasonal succession of communities. The structural heterogeneity of the shrubby habitats is responsible for a more complicated and site-specific differentiation of communities; oribatid species of shrubby sites are either capable of inhabiting the open sites as well or persist throughout the whole year.
Abstract: The effect of pollution of urban soils by traffic exhausts on oribatid mites was studied along a traffic gradient of the city of Thessaloniki. Although the population density of the main orbatid species appeared increased in polluted areas, the total oribatid numbers were reduced due to the reduction in species richness. The highest species diversity was recorded in moderately polluted areas. The morphometric characteristics as well as certain life-history traits did no correlate with the level of traffic influence. Nevertheless, these characteristics were considered important for the understanding of the pollution impact on life in soils. Moderate body size, sexual reproduction, increased reproductive effort and wide habitat preferences characterize species in urban sites. Scheloribates latipes and Tectocepheus sarekensis can be used as bioindicators for Pb and Zn pollution of soils, respectively.
Abstract: The present paper presents results on the metabolic activity of adults of three oribatid species (Scheloribates cf. latipes, Pilogalumna allifera and Achipteria oudemansi), inhabiting the upper soil layers of a mediterranean pasture land, covered by evergreen-sclerophyllous shrubs. Oxygen consumption was recorded at six temperatures for three subsequent days to determine the respiration rate-temperature relationship and to describe the acclimation process to constant temperature conditions. The response of the animals to temperature changes was also determined. Low respiration rates and Q(10) values, a relative thermal independence at temperature extremes and an acute response to temperature increase are the main metabolic characteristics of the animals. These results are discussed in relation to the life cycle characteristics of the species in the field.
Abstract: The effect of a summer wildfire on the abundance and community composition of soil macroinvertebrates of a phryganic ecosystem was studied. The numerical responses of macroinvertebrates to fire were variable, most notably the reduction of the saprophagous fauna. The magnitude of the changes in abundance due to fire was comparable or even lower than the variations imposed by the seasonality of the mediterranean climate. fire did not seem to affect strongly the community composition of the soil inhabiting fauna, but caused considerable changes in the composition of the litter-dwellers. Furthermore, seasonal changes in community composition were less pronounced in the burnt site compared to those in the control. The observed effects of fire should be attributed to the destruction of the litter layer and the above ground vegetation cover, rather than to the immediate death of the animals, since most of them were absent from the upper soil layers during summer, that is when fire occured.
Abstract: The temporal and spatial distribution of collembolans in a grazed maquis formation was studied. The seasonality of the mediterranean climate determines the temporal pattern of the collembolan community in the study area, while the main spatial gradient, along which the community is ordinated, is from open to sheltered microhabitats. The vegetation structure, resulting from grazing pressure, determines the spatial distribution of the collembolan species, mainly through its effect on the microenvironmental conditions of the habitat.
Abstract: The arthropod colonization patterns in the decomposing litter of a Quercus coccifera formation in northern Greece was studied by using litter bags of different mesh sizes. No difference was recorded between the two litter bag sets used, with respect to the total dry mass loss, which did not exceed 40 % after two years. Changes in the numbers of arthropods in the upper litter layers parallel the seasonal fluctuations of the abiotic parameters. Temperature was found to control mainly oribatid numbers, while numbers of Collembola and the rest of the arthropods studied are influenced by both litter water content and temperature. Seasonality prevents the establishment of a resident arthropod fauna in the litter bags during the early decomposition stages. Differences in the experimental treatment of litter in the two experiments are also discussed.
Abstract: Oxygen consumption of Onychiurus meridiatus (Collembola: Onychiuridae) at six experimental temPeratures was determined by means of the gradient diver technique. Log10 respiration rate was linearly related to log10 live weight, with a mean regression coefficient of 0.64. Asymmetry at thermal optimum characterized the metabolic response to the elevation of temperature. Respiration rate rose sigmoidly up to 26-degrees-C and decreased exponentially beyond this point and up to thermal maximum. Acclimation at constant temperature conditions resulted in a depression of oxygen consumption. As regards mature individuals, this depression was significant throughout the whole temperature range studied, while regarding immatures it was significant only at high temperatures. The above results are discussed in relation to the special characteristics of the life cycle development of the species in the laboratory and in the field.
Abstract: A model is formulated aiming to describe census data for populations changing non-symmetrically with time. The model is based on the concept of ecological time. conceived as an environmental gradient. A method of changing time scales, by using a periodic equation relating ecological to standard clock time unit, is presented. The model has been applied to simulate phenological curves of population abundance for oribatid mites and Collembola from a Mediterranean ecosystem. The concept of ''phase difference continuum'' is introduced and the life history strategies of oribatids and Collembola are discussed. Asymmetries as well as synchronizations in population development, annual periodicity and inter-annual stability, are common features for almost all populations studied, summer drought being the adverse period for the majority of them. Precocity, iteroparity and high rate of juvenile development into successive stages during the favourable period, hold for all phenological patterns. Adults' demographic parameters and the animals' ability for altering their physiological status are the characteristics discriminating between various strategies. Most Collembola display left-skewed phenology, while most oribatids display a right-skewed one.
