Regular ArticlePopulation Level Consequences of Toxicological Influences on Individual Growth and Reproduction inLumbricus rubellus(Lumbricidae, Oligochaeta)
Abstract
The effects of increased environmental concentrations of copper on the population dynamics ofLumbricus rubellusare investigated. A size-structured matrix model is used to translate sublethal effects on individual growth and reproduction into their population dynamical consequences. Laboratory data on growth and reproduction under different, sublethal conditions of copper stress are used to parameterize the model. An estimate for the critical threshold concentration of copper (critical in a sense that the population growth rate at this concentration equals zero), obtained from the model analysis, agrees well with observations on field populations ofL. rubellus.
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Contribution of anecic and epigeic earthworms to biological control of Fusarium graminearum in wheat straw
2021, Applied Soil EcologyEarthworms have proved to contribute to plant health indirectly, by improvement of soil physical and chemical properties, as well as directly, through suppression of plant pathogens. Fusarium Head Blight, caused primarily by Fusarium graminearum, is one of the most important cereal diseases, with severe detrimental effects on yield and grain quality worldwide, and significant effect on grain safety due to the accumulation of mycotoxins produced by the fungus. Earthworms could reduce the residue-borne inoculum density of F. graminearum through different mechanisms, including direct competition by residue consumption, growth inhibition caused by the earthworm coelomic fluid, mechanical disruption of fungal hyphae, and burying crop residue which reduce the chances for the fungus to release spores for head infection. Thus, the aim of this study was to assess the effects of anecic and epigeic earthworms on wheat straw and on F. graminearum inoculum. For this, PVC cylinders (microcosms 14.5 cm diameter, 30 cm height) were filled with moist soil mix, wheat straw was evenly distributed on the soil surface (inoculated with Fusarium, soil microorganisms or sterile) and three earthworm species (Aporrectodea longa, Lumbricus rubellus or Lumbricus terrestris) were tested. Since the response of earthworms may change according to conditions of soil moisture and food availability, two different experiments were arranged. The first Experiment represented a sub-optimal situation for earthworms regarding soil moisture and feeding conditions, which was obtained by scarce watering of the microcosms with a consequent decrease in soil water content during incubation, and by not adding cow manure as supplementary food source. In the second experiment, soil was enriched with cow manure as feed for the earthworms and soil moisture was maintained above 25%. Results from qPCR analysis revealed that F. graminearum inoculum on straw was reduced to undetectable amounts by L. rubellus and A. longa when the feeding conditions were limited, while no significant differences compared with the control without earthworms were found when earthworms had high food availability (α = 0.05). Straw coverage on soil surface was reduced by L. rubellus (epigeic) in both experiments (p < 0.0001), while A. longa (anecic) just did so under optimal conditions. L. terrestris (anecic), only tested under optimal conditions, reduced soil cover significantly more than the other two species (p < 0.0001). Negative effect of this fungus was not observed on the studied earthworms. Both anecic and epigeic earthworms tested showed potential to contribute to biological control of F. graminearum in wheat straw. This control may occur by reducing straw on surface, reducing the pathogen inoculum on straw, or both, depending on the environmental conditions and their response according to their ecological group and species. The possibilities to optimize earthworm capacity for biological control of fungal diseases in practical agriculture, under changing weather and organic matter supply conditions, are discussed.
How including ecological realism impacts the assessment of the environmental effect of oil spills at the population level: The application of matrix models for Arctic Calanus species
2018, Marine Environmental ResearchFor oil spill responses, assessment of the potential environmental exposure and impacts of a spill is crucial. Due to a lack of chronic toxicity data, acute data is used together with precautionary assumptions. The effect on the Arctic keystone (copepod) species Calanus hyperboreus and Calanus glacialis populations is compared using two approaches: a precautionary approach where all exposed individuals die above a defined threshold concentration and a refined (full-dose-response) approach. For this purpose a matrix population model parameterised with data from the literature is used. Population effects of continuous exposures with varying durations were modelled on a range of concentrations. Just above the chronic No Observed Effect Concentration (which is field relevant) the estimated population recovery duration of the precautionary approach was more than 300 times that of the refined approach. With increasing exposure concentration and duration, the effect in the refined approach converges to the maximum effect assumed in the precautionary approach.
EGrowth: A global database on intraspecific body growth variability in earthworm
2018, Soil Biology and BiochemistryEarthworms play a key role in soil and ecosystem functioning. Predicting their abundance and spatial distribution is required to understand their ecological role. There is growing evidence that mechanistic models of earthworm population dynamics are promising tools to tackle this issue. However, this approach requires a fair amount of data because it explicitly integrates the three fundamental biological processes: growth, reproduction and mortality. Hitherto, the lack of comprehensive databases on life history parameters related to these three processes hampered the widespread development of mechanistic earthworm population dynamics models. As a consequence, predicting earthworm abundance in a variety of conditions across species is still difficult.
The clear bottleneck for making progress is the lack of databases on the intraspecific variability of earthworm life history traits in response to environmental conditions. Data related to body growth and body size are critical because body size largely determines reproduction and mortality rates. Body growth is therefore the backbone of mechanistic models of earthworm population dynamics.
Here I present EGrowth, the first comprehensive database on intraspecific variability of earthworm body growth in relation to environmental conditions. The EGrowth database contains 1073 growth curves of 51 species of earthworms, representing 16002 measures of body mass. It covers publications on earthworm body size from 1900 to 2016. The environmental conditions in which the growth curves were produced are also reported. The database is open access and can be browsed from a graphical user interface. EGrowth will be updated regularly in the future as new studies are published. I propose a standardized framework for reporting future data on body growth of earthworms.
Fish life-history traits are affected after chronic dietary exposure to an environmentally realistic marine mixture of PCBs and PBDEs
2018, Science of the Total EnvironmentCitation Excerpt :Developing such a model to investigate the effects of an environmentally realistic marine mixture of PCBs and PBDEs would allow assessing (i) whether changes in growth and reproduction can be independent or not by testing theoretically different physiological mode of actions and (ii) whether they could compensate each other in terms of consequences on lifetime reproductive output and fitness. Contaminant exposure may have serious implications for population dynamics and, consequently, on the structure of ecosystems as shown in many species (Barnthouse et al., 1990; Klok and de Roos, 1996; Munns et al., 1997). However, the effects of POPs on the population dynamics of fish, especially on exploited marine fish, are still poorly investigated.
Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants that have been shown to affect fish life-history traits such as reproductive success, growth and survival. At the individual level, their toxicity and underlying mechanisms of action have been studied through experimental exposure. However, the number of experimental studies approaching marine environmental situations is scarce, i.e., in most cases, individuals are exposed to either single congeners, or single types of molecules, or high concentrations, so that results can hardly be transposed to natural populations. In the present study, we evaluated the effect of chronic dietary exposure to an environmentally realistic marine mixture of PCB and PBDE congeners on zebrafish life-history traits from larval to adult stage. Exposure was conducted through diet from the first meal and throughout the life cycle of the fish. The mixture was composed so as to approach environmentally relevant marine conditions in terms of both congener composition and concentrations. Life-history traits of exposed fish were compared to those of control individuals using several replicate populations in each treatment. We found evidence of slower body growth, but to a larger asymptotic length, and delayed spawning probability in exposed fish. In addition, offspring issued from early spawning events of exposed fish exhibited a lower larval survival under starvation condition. Given their strong dependency on life-history traits, marine fish population dynamics and associated fisheries productivity for commercial species could be affected by such individual-level effects of PCBs and PBDEs on somatic growth, spawning probability and larval survival.
Density-dependent responses in some common lumbricid species
2017, PedobiologiaIt 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.
Earthworm assemblages as affected by field margin strips and tillage intensity: An on-farm approach
2015, European Journal of Soil BiologyEarthworm species contribute to soil ecosystem functions in varying ways. Important soil functions like structural maintenance and nutrient cycling are affected by earthworms, thus it is essential to understand how arable farm management influences earthworm species. One aim of arable field margin strips and non-inversion tillage is to enhance agrobiodiversity, however their influence on earthworm species assemblages remains unclear. In particular, on-farm studies conducted over multiple years that capture variability across the landscape are rare. The current study monitored earthworm species assemblages on 4 farms in Hoeksche Waard, The Netherlands, from 2010 to 2012. It was hypothesised that arable field margin strips (FM) and non-inversion tillage (NIT; a reduced tillage system that loosens subsoil at 30−35 cm depth) would have higher earthworm species abundances (epigeics and anecics in particular), soil organic matter, and soil moisture than adjacent mouldboard ploughing (MP) fields, and that earthworm numbers would decrease with distance away from FM into arable fields (MP only). FM contained a mean total earthworm abundance of 284 m−2 and biomass of 84 g m−2 whereas adjacent MP arable fields had only 164 earthworms m−2 and 31 g m−2. Aporrectodea rosea, Lumbricus rubellus, Lumbricus terrestris, and Lumbricus castaneus were significantly more abundant in FM than adjacent arable soil under MP. However, no decreasing trend with distance from FM was observed in earthworm species abundances. A tillage experiment initiated on the farms with FM showed that relative to MP, NIT significantly increased mean total earthworm abundance by 34% to 275 m−2 and mean total earthworm biomass by 15% to 51 g m−2 overall sampling dates and farms. L. rubellus, A. rosea, and L. terrestris were significantly more abundant overall in NIT than MP. FM and NIT positively affected earthworm species richness and abundances and it is noteworthy that these effects could be observed despite variation in environmental conditions and soil properties between samplings, farms, and crops. Higher top-soil organic matter and less physical disturbance in FM and NIT likely contributed to higher earthworm species richness and abundances. The anecic species L. terrestris (linked to water infiltration and organic matter incorporation) was more abundant in FM, but densities remained very low in arable soil, irrespective of tillage system.