Search

A domination of generalist predators in soil communities suggests a wide overlap in their prey spectra, resulting in a probability of tense trophic relationships within the predator complex, in particular during the periods of prey scarcity caused by natural community reorganisations or anthropogenic disturbance. It has been argued that soil physical structure (e.g. pore size and connectivity) can limit interactions between the potential trophic competitors facilitating their coexistence (Erktan et al., 2020). Another possible mechanism of coexistence of generalist predators would be a variation in their life history traits resulting in a certain partitioning of their trophic niches. On an example of a field experiment studying soil mesofauna succession in decomposing plant remains, we compared potential trophic spectra of the abundant predators (firstly, gamasid mites), outlined by significant correlations of their densities with densities of other members of the community. A wide variation of potential prey objects was revealed for the major predators which thus should be treated as generalist feeders with activities spanning over several trophic levels. At the same time, the predators were characterised by individual spectra of the potential prey taxa and a low interspecific similarity between these spectra. The results suggest a certain differentiation of trophic niches in the mesofauna predatory complex. In addition, the prey spectra underwent temporal changes in the course of mesofauna succession, indicating possible switching of predators between the prey objects in response to environmental changes during the decay process. [ABSTRACT FROM AUTHOR]

A striking feature of predatory complex in soil communities is a domination of generalist predators and a wide overlap in the prey spectra of the major predators, combined with usual intraguild predation and cannibalism. This suggests a probability of tense trophic relationships between the major predator taxa, in particular during the periods of community reorganisations and/or prey scarcity caused by natural or anthropogenic disturbance. On an example of a field experiment modelling the process of mesofauna community development after the ploughing of an organic fertiliser into soil, dynamics of major predators (Mesostigmata and trombidiform mites, insect larvae) was followed in detail. It was shown that patterns of population dynamics of the dominant predatory taxa markedly differed and their density peaks were distinctly separated. A preliminary explanation suggests that this differentiation was determined to a large extent by the interactions between the predatory taxa (like partitioning of prey objects and/or avoidance of intraguild predation). [ABSTRACT FROM AUTHOR]

A striking feature of predatory complex in soil communities is a domination of generalist predators and a wide overlap in the prey spectra of the major predators, combined with usual intraguild predation and cannibalism. This suggests a probability of tense trophic relationships between the major predator taxa, in particular during the periods of community reorganisations and/or prey scarcity caused by natural or anthropogenic disturbance. On an example of a field experiment modelling the process of mesofauna community development after the ploughing of an organic fertiliser into soil, dynamics of major predators (Mesostigmata and trombidiform mites, insect larvae) was followed in detail. It was shown that patterns of population dynamics of the dominant predatory taxa markedly differed and their density peaks were distinctly separated. A preliminary explanation suggests that this differentiation was determined to a large extent by the interactions between the predatory taxa (like partitioning of prey objects and/or avoidance of intraguild predation). [ABSTRACT FROM AUTHOR]

It is generally accepted that populations of most species experience some level of density dependence; however, this has rarely been shown for soil-dwelling invertebrate species, in particular for earthworms. Experimental data, mostly obtained at high laboratory densities, suggest intense intraspecific competition for resources and/or living space and density-dependent dynamics in earthworm populations, irrespective of their ecological group affiliation. In the present study performed in large field microcosms, I investigated whether density-dependent responses occur within the earthworm density gradients more realistic for the natural sites. Five lumbricid species from epigeic ( Dendrobaena octaedra , Lumbricus rubellus ), endogeic ( Allolobophora chlorotica , Aporrectodea caliginosa ) and anecic ( Lumbricus terrestris ) ecological groups were tested. Soil systems populated with earthworm monocultures in large (20-L) microcosms were exposed in a beech-oak forest for 4.5 months; each species was represented by two ( L. terrestris ) or three treatments forming gradients of increasing density. In two endogeic species, manifold and generally similar density-dependent responses (a retardation of growth, maturation and reproduction rates, but higher mortality rates with density increase) were revealed, likely explained by spatial competition rather than by direct food competition. In each of epigeic species density-dependent responses were less variable and more species-specific. In contrast to endogeics, direct food competition was presumably a more important cause of density-dependence. In L. terrestris no significant density-dependent responses in adult earthworms were revealed; however, they need to be further investigated in relation to the age and territorial behaviour of individual earthworms. Importantly, in any earthworm species the density variations in the reproducing generation had significant consequences for the advancing generation, affecting either the numbers or/and the size (individual weight) of the cocoons produced. It is suggested that an underestimation of density-dependent processes may cause inaccurate estimates of the activities of local lumbricid populations. [ABSTRACT FROM AUTHOR]

Lumbricids and enchytraeids are two keystone fauna groups strongly responsible for the functioning of detrital food webs in temperate soils but acting at contrasting spatial scales. The relationships between both groups are poorly understood: considering their close kinship and trophic habits as generally microbi-/saprovores, competitive interactions are expected. However, due to engineering activities, various non-trophic earthworm impacts on enchytraeids also play a role, which has never been evaluated. We experimentally simulated and quantitatively estimated the effects of major non-trophic earthworm activities (burrowing, cast deposition, mucus release) and, in addition, of earthworm mortmass decay on the abundance of enchytraeids. Effects of two earthworm species belonging to epigeic (Lumbricus rubellus) and endogeic (Aporrectodea caliginosa) ecological groups were tested. Non-trophic earthworm effects strongly varied (a) between the types of activity (burrowing, casts, mucus), (b) across the soil profile, (c) between the earthworm species. In general, enchytraeids responded positively to earthworm non-trophic activities. Mucus release and burrowing showed usually stronger impacts than cast deposition. The participation of different non-trophic effects in the resulting joint effect (burrowing + casts + mucus) varied with earthworm species and soil horizon. Decomposition of dead earthworms stimulated enchytraeid abundance at lower, but inhibited it at higher mortmass amount. A comparison between enchytraeid responses to live earthworm (integrated trophic and non-trophic activities) and joint non-trophic (burrowing + casts + mucus) impacts allowed an approximate separation of both activity types. Rates of trophic and non-trophic impacts were quantitatively comparable and earthworm species-specific. In particular, L. rubellus and A. caliginosa earthworms rendered adverse (negative and positive, respectively) influence on enchytraeid abundance. It was concluded that the negative effects of live L. rubellus on enchytraeids were primarily related to its trophic activity, whereas the positive effects of live A. caliginosa were strongly connected with its non-trophic activities. [ABSTRACT FROM AUTHOR]

Abstract: Temperature fluctuations are a fundamental entity of the soil environment in the temperate zone and show fast (diurnal) and slow (seasonal) dynamics. However, responses of soil ecosystem engineers, such as earthworms, to annual temperature dynamics are virtually unknown. We studied growth, mortality and cocoon production of epigeic earthworm species (Lumbricus rubellus and Dendrobaena octaedra) exposed to temperature fluctuations in root-free soil of a mid-European beech–oak forest. Both earthworm species (3 + 3 individuals of each species) were kept in microcosms containing soil stratified into L, F + H and Ah horizons. In the field, earthworm responses to smoothing of diurnal temperature fluctuations were studied, simulating possible global change. In the laboratory, earthworm responses to seasonal (±5 °C of the annual mean) and diurnal temperature fluctuations (±5 °C of the seasonal levels) were analyzed in a two-factorial design. Both experiments lasted 12 months to differentiate between seasonal and diurnal responses. In the third experiment overwintering success of both earthworm species was investigated by comparing effects of constant temperature regime (+2 °C), and daily or weekly temperature fluctuations (2 °C ± 5 °C). Temperature regime strongly affected population performance of the earthworms studied. In the field, smoothed temperature fluctuations beneficially affected population development of both earthworm species (higher biomass, faster maturity and reproduction, lower mortality). Consequently, density of both species increased faster at smoothed than at ambient temperature conditions. In the laboratory, responses of L. rubellus and D. octaedra to temperature treatments differed; however, in general, earthworms benefited from the absence of diurnal fluctuations. Total earthworm numbers were at a maximum at constant temperature and lowest in the treatment with both diurnal and seasonal temperature fluctuations. However, after one year L. rubellus tended to dominate irrespective of the temperature regime. In the overwintering experiment L. rubellus sensitively responded to even short-term winter frost and went extinct after one week of frost whereas D. octaedra much better tolerated frost conditions. Earthworms of both species which survived frosts were characterized by a significant body weight decrease during the period of frosts and fast recovery in spring suggesting a different pattern of individual resource expenditure as compared with constant +2 °C winter regime. Contrasting trends in the population dynamics of L. rubellus and D. octaedra during the frost-free period and during winter suggest that in the long-term temperature fluctuations contribute to the coexistence of decomposer species of similar trophic position in the forest litter. The results are discussed in context of consequences of climate change for the functioning of soil systems. [Copyright &y& Elsevier]

Summary: Earthworm species differentially affect organic matter and energy transformations, and interrelationships among soil food web components. Hence, knowledge of earthworm species associations and their interactions is important not only for an understanding of the functioning of soil systems and predicting the consequences of invasions of peregrine earthworms for native earthworm fauna, soil food web structure and functioning, but also for the structure and functioning of the aboveground food web. Over 60 studies investigating a total of 19 species and about 20 response variables were studied to summarize the scattered information on inter- and intraspecific interactions in lumbricids. Information on interactions between species is restricted to species pairs, while there is no data on species interactions within more complex associations. For further analysis, interactions were classified into positive and negative (i.e., those enhancing or decreasing the fitness of a given species). Based on this approach, “interactive portraits” (combinations of responses and effects) for six widespread species and for major ecological groups of earthworms were composed. Species and group characteristics were confirmed by meta-analysis. In multispecies communities, species strongly react to species composition and community structure with the mechanisms of species interactions likely being context-specific. Interactions between both species and ecological groups strongly affect soil biota and soil processes, with synergistic and neutralizing effects being most important. At the species level, lumbricids are among the few groups of soil invertebrates where density-dependent regulation of populations appears to be prevalent. These conclusions have important implications for the role of earthworms acting as ecosystem engineers in terrestrial systems. [Copyright &y& Elsevier]

Abstract: Temperature fluctuations are a fundamental entity of the soil environment in the temperate zone and show fast (diurnal) and slow (seasonal) dynamics. Responses of soil respiration to temperature fluctuations were investigated in a root-free soil of a mid-European beech–oak forest. First, in laboratory we analysed the efflux of CO2 from soil microcosms exposed to seasonal (±5°C of the annual mean) and diurnal fluctuations (±5°C of the seasonal levels) in a two-factorial design. Second, in field microcosms we investigated effects of smoothing diurnal temperature fluctuations in soil (simulating a possible global trend) on CO2 efflux. Third, the natural temperature regime was simulated in laboratory microcosms and their CO2 efflux was compared to the one in the field. The experiments lasted for 1 year to differentiate seasonal and annual responses. Dynamics of CO2 efflux, microbial basal respiration, biomass and qO2 varied with seasonal temperature regime. However, in the laboratory the annual cumulative CO2-C production did not differ between treatments and varied between 10.9% and 11.7% of the total microcosm C, disregarding seasonal and/or diurnal fluctuations. The similarity of cumulative C production suggests that the availability of microbially mobilisable carbon pools rather than the temperature regime limited soil respiration. Diurnal fluctuations generally did not affect CO2 efflux and microbial activity, though winter Q 10 values were increased in their absence. Simulation of the natural temperature regime in the laboratory resulted in CO2 efflux similar to field microcosms. In the field, rates of CO2 efflux and microbial activity, seasonal and annual cumulative CO2-C production were significantly higher at smoothed than at natural temperature conditions (annually 13.1% and 11.0% of total C was respired, respectively). Facing global climate changes the mechanisms regulating responses of soil respiration to temperature fluctuations need further investigation. [Copyright &y& Elsevier]

Rates of carbon dioxide production of cocoons, juveniles and matures of Lumbricus rubellus were measured at five constant (2°C, 5°C, 10°C, 15°C, 20°C) and three diurnally fluctuating temperature regimes (0–10°C, 5–15°C, 10–20°C) covering the whole range of temperature conditions experienced by this species in forests in Central Germany. Respiration rates of developmental stages significantly increased with temperature both under constant and fluctuating regimes. Overall, at constant temperature regimes Q10 values for cocoons, juvenile and mature earthworms were 1.6, 2.7 and 2.0, respectively. At fluctuating temperature regimes Q10 values were generally higher with 2.4, 3.6 and 3.5 for cocoons, juvenile and mature earthworms, respectively. At the same mean temperature respiration rates at fluctuating regimes exceeded those at constant regimes in all developmental stages. [Copyright &y& Elsevier]

Abstract: Earthworm population densities vary strongly in space and time, and it has been hypothesised that the metabolic activity of the epigeic species Lumbricus rubellus and Dendrobaena octaedra is influenced by the presence of conspecifics. Carbon dioxide production of mature earthworms of these two species kept separately or in groups of two (L. rubellus) and three individuals (D. octaedra) were measured at constant and diurnally fluctuating temperature regimes. In L. rubellus respiration rates at constant and fluctuating regimes did not differ between specimens kept individually and in groups. In contrast, in D. octaedra both respiration rates and reproduction were significantly lower in earthworms kept in groups as compared to specimens kept individually. [Copyright &y& Elsevier]

Summary: Population responses of a forest floor saprotrophic mite, Nothrus silvestris (Oribatei), were studied in litter microcosms for 14 weeks under three temperature regimes. The regimes reflected a range of diurnal fluctuations (T10–20 and T5–25 - daily fluctuations from 10 to 20 °C and 5 to 25 °C, respectively) around a mean of 15 °C (constant regime, T15). The T5–25 regime was unfavourable, leading to the highest mortality and the lowest reproduction rates in the mite parental population. Moderate fluctuations (T10–20 regime) caused the lowest mortality and the highest offspring production and therefore, the highest population growth in N. silvestris. Population responses were intermediate under the T15 regime. Thus, a trade-off between reproduction and adult mite survival that is regulated by temperature regime seems to exist in N. silvestris. Similar trends of population responses to temperature regime were observed in another litter mite, Schwiebea sp. (Acaroidea), which was also collected from the microcosms. [Copyright &y& Elsevier]

The article discusses a study that examines the spatial distribution and species co-occurrence in soil invertebrate and plant communities on northern taiga islands. The study describes the patterns of species association across taxa and trophic groups using a data set on arctic plant and animal species obtained from arctic islands of the Kandalasha Bay. It reveals high frequency of significantly segregated taxa on the relatively stable forested island.

Soil animals perform a range of essential ecosystem functions and can modify the effects of global change on terrestrial ecosystems. We evaluated responses of six major groups of soil animals (Acari (all groups), Oribatida, Collembola, Insecta, Nematoda, and Oligochaeta) to controlled changes in air temperature, precipitation level or carbon dioxide concentration by using random-effects modelling and mixed-effects meta-regression modelling. Along with the three global change factors, sixteen local climatic characteristics (such as mean annual temperature, Köppen climate classification, vegetation type) were tested. Overall, 86 studies comprising 236 observations with mean duration of 51 months were selected as relevant for the analysis. Quantitative links between global change factors, local climate characteristics and changes in abundance of four taxonomic groups of soil animals were revealed. Warming and precipitation level were associated most strongly with population dynamics of soil invertebrates compared to elevated atmospheric CO 2. Each 1 °C increase in air temperature was correlated with a mean of 12.5% (95% CI: 2.5%–22.6%) increase in Acari abundance, while populations of Collembola were declined by 9.6% (95% CI: −17.8% to −1.4%). Meanwhile, each 10% increase in precipitation level was correlated with the increase in the abundance of Nematoda by 1.4% (95% CI: −7.6% to 10.4%) and Oligochaeta by 34.7% (95% CI: 8.1%–61.2%). Considering IPCC estimates (SSP3-7.0 Scenario) of an average climate warming by 3.6 °C and a substantial variation in local precipitation levels (up to ±20%) by the end of the 21st century, strong local changes in the structure of detrital food webs are predicted by meta-regression models. In regions with decreased precipitation, the formation of soil food webs promoting carbon mineralization may be expected, while in regions with increased precipitation, the changes in detrital food web structure can contribute to the accumulation of carbon in the soil. • Responses of soil invertebrates to major climate change factors were studied by meta-analysis. • Warming and precipitation levels better predicted soil fauna responses than elevated CO 2 levels. • Each 1 °C increase correlated with 12.5% of Acari abundance increase. • Each 1 °C increase correlated with 9.6% of Collembola abundance decrease. • By yr 2100, strong regional changes in structure of detrital food webs were predicted. [ABSTRACT FROM AUTHOR]