The contribution of a niche-based approach to ecological risk assessment: using macroinvertebrate species under multiple stressors

Long-term recovery dynamics determined by the degree of the disturbance - Ten years tracking of aquatic macroinvertebrate recolonisation after an industrial disaster (Red Sludge Disaster, Hungary)

A ten-year-long examination of macroinvertebrate community recovery was conducted following a catastrophic spill of highly alkaline red sludge (pH >13) into lowland streams. Our primary objective was to compare recovery patterns after coarse- and fine-grain disturbances, focusing on two aspects: i) trend analysis to reveal long-term changes of six community parameters, and ii) variation analyses to assess parameter changes over time. We conducted statistical analysis on long-term data series of macroinvertebrates obtained from quantitative samples collected at four sections with varying degrees of disturbance along the impacted stream sections. We developed a comprehensive theoretical framework comprising a series of sequential phases: Ramp-up, Overshoot, and Oscillation Phases. i) A trend analysis revealed that disturbances show a gradual recovery pattern, while variance analyses showed an asymptotic convergence to an equilibrium. ii) Evaluating these trends across phases unveiled that the initial recovery phase exhibited a steep trajectory, lasting 4-9 months, irrespective of disturbance severity. Coarse-grain disturbances induced a remarkable Overshoot phenomenon across all community metrics. The more severe the disturbance, the greater the height and duration of the Overshoot. Our results suggest that the presence or absence of Overshoot can serve as an indicator for coarse-grain disturbances in the context of large and infrequent disturbances (LID). The entire recovery process lasts for 2.5-3 years irrespective of the severity of the LID. In conclusion, a minimum survey duration of two and half years is deemed imperative to capture the phases of recovery, and changes associated with LID are not expected to extend beyond the three-year threshold. The theoretical framework, including Overshoot parameters, may assist future studies in comparing recovery patterns of different LID types. Furthermore, our theoretical framework is likely to be applicable to other groups of organisms given a sufficiently long monitoring of recovery, influenced also by the length of reproductive cycles.

Invader abundance and contraction of niche breadth during replacement of a native gammarid amphipod

The introduction of non‐native species to new locations is a growing global phenomenon with major negative effects on native species and biodiversity. Such introductions potentially bring competitors into contact leading to partial or total species replacements. This creates an opportunity to study novel species interactions as they occur, with the potential to address the strength of inter‐ and intraspecific interactions, most notably competition. Such potential has often not been realized, however, due to the difficulties inherent in detecting rapid and spatially expansive species interactions under natural field conditions. The invasive amphipod crustacean Gammarus pulex has replaced a native species, Gammarus duebeni celticus, in river and lake systems across Europe. This replacement process is at least partially driven by differential parasitism, cannibalism, and intraguild predation, but the role of interspecific competition has yet to be resolved. Here, we examine how abundance of an invasive species may affect spatial niche breadth of a native congeneric species. We base our analyses of niche breadth on ordination and factor analysis of biological community and physical parameters, respectively, constituting a summative, multidimensional approach to niche breadth along environmental gradients. Results derived from biological and environmental niche criteria were consistent, although interspecific effects were stronger using the biological niche approach. We show that the niche breadth of the native species is constrained as abundance of the invader increases, but the converse effect does not occur. We conclude that the interaction between invasive G. pulex and native G. d. celticus under natural conditions is consistent with strong interspecific competition whereby a native, weaker competitor is replaced by a superior invasive competitor. This study indicates a strong role of interspecific competition, alongside other known interactions such as differential intraguild predation, in rapid and expansive species replacements following biological invasions.

Decline in niche specialization and trait β-diversity in benthic invertebrate communities of Central European low-mountain streams over 25 years

Biotic homogenization is one of the key aspects of the current biodiversity crisis. Here we analyzed the trends of three facets of niche homogenization, i.e. niche specialization, trait α-diversity and spatial β-diversity, over a period of 25 years (1990-2014) using a large dataset of 3782 stream benthic invertebrate samples collected from central European low-mountain streams. We studied a set of traits describing the ecological niche of species and their functions: body size, feeding groups, substrate preferences, flow preferences, stream zonation preferences and saprobity. Trait composition changed significantly during the study period, and we identified an overall increase in niche homogenization. Specifically, community niche specialization significantly decreased by 20.3% over the 25-year period, with declines ranging from -16.0 to -40.9% for zonation-, flow-, substrate-preferences, body size and feeding traits. Trait diversity did not change significantly, although we recorded significant decreases by -14.2% and -10.2% for flow- and substrate-preference and increases by 5.8% and 22.6% for feeding traits and zonation preference over the study period. Trait spatial β-diversity significantly decreased by -53.0%, with substrate-preference, feeding groups and flow-preference traits declining from -61.9% to -75.3% over the study period. This increased niche homogenization is likely driven by the increase of down-stream typical taxa, which are favored by warming temperatures. Further, it is in apparent contradiction with the recorded increase in abundance (+35.9%) and taxonomic richness (+39.2%) over the same period. Even such increases do not safeguard communities from undergoing niche homogenization, indicating that recovery processes may differ with regard to community taxonomic composition and traits. Our results emphasize the complexity of community responses to global change and warrant caution when founding conclusions based solely on single community metrics.

A system-scale environmental risk analysis with considering a conceptual conversion from material/energy flow to information flow under uncertainties

A conceptual conversion from material/energy flow to information flow is presented in this study for evaluating network environment analysis (NEA) within the naphthalene-contaminated groundwater ecosystems under stochastic-fuzzy uncertainties. Four components (i.e., vegetation, herbivore, soil microorganism, and carnivore) are considered into the NEA framework for quantifying their direct and integral ecological risks. Carcinogenic risk related to human health concern is also evaluated under four remediation periods. The developed method is then applied to a power plant site. Results reveal that the average naphthalene concentration after pump-and-treat treatment would significantly decrease from 8.672 to 1.232 μg/L when remediation period extends to 10 years. The probabilities of suffering from carcinogenic risk would reach 0.9862, 0.9566, 0.8746, and 0.6142 under different remediation periods. Soil microorganism would receive more input risk than vegetation owing to its higher vulnerability. Although the upper-layer components (such as herbivore and carnivore) are not exposed to risk sources, they would gradually accumulate to a high-level ecological risk through food chains. Sensitivity analysis shows that variations in standard boundaries would have a significant impact on the risks of all components within groundwater ecosystems. This study can offer a novel perspective and methodology for comprehensively assessing the system-scale environment risks.

Taxonomic and non-taxonomic responses of benthic macroinvertebrates to metal toxicity in tropical reservoirs. The case of Cantareira Complex, São Paulo, Brazil

Benthic macroinvertebrates are organisms that are recognized as water quality bio-indicators. A wide variety of indices and metrics have been shown to respond to a variety of anthropogenic impacts, usually under a general condition of environmental impairment. The absence of a clear distinction in the relations between specific pollutants and biotic variables is very common and can lead to biased interpretation of biomonitoring. The aims of this research were to test taxonomic and non-taxonomic responses to specific environmental conditions instead to general conditions. For this purpose, we estimated the theoretical toxicity by comparing toxicity values published by EPA with metal concentrations in water and sediments. Then we tested the responses of biological variables to toxicity and other environmental conditions using the linear mixed effects models approach. We generated 32 models considering 24 different biological metrics and indices that were grouped in five levels. Taxonomic and abundance metrics were best predictor than functional or tolerance-based indexes. The strongest model was that which considered subfamily taxonomic resolution responding to Al_w and Cr_s.

Variation in isotopic niche, digestive tract morphology, and mercury concentrations in two sympatric waterfowl species wintering in Atlantic Canada

Sympatric communities of organisms may exploit different ecological niches to avoid intra- and interspecific competition. We examined the isotopic niches of American black ducks ( Anas rubripes) and mallards ( A. platyrhynchos) wintering in coastal and urban areas of Atlantic Canada and compared isotopic niche with digestive tract morphologies and blood mercury (Hg) concentrations. Isotopic niche width (for δ13C and δ15N) varied between the three groups of ducks studied, with coastally foraging black ducks exhibiting the widest isotopic niche, followed by coastal mallards, while urban feeding black ducks had a narrow isotopic niche. These niche differences had physical and chemical consequences: coastal black ducks had longer digestive tracts, a larger range in gizzard sizes, and higher and more variable Hg concentrations than urban black ducks and coastal mallards. This plasticity in ecological niche may reduce competition among and within species, and subsequently explain why winter numbers of black ducks and mallards have increased in Atlantic Canada.

Single and joint oxidative stress-related toxicity of sediment-associated cadmium and lead on Bellamya aeruginosa

The biotoxicity of heavy metals in sediments toward benthic organisms has evoked great concern for the health of freshwater ecosystems. This study applied a sediment toxicity testing protocol to investigate the single and joint toxicity of cadmium (Cd) and lead (Pb) on Bellamya aeruginosa. B. aeruginosa were exposed to different concentrations of Cd (5, 25, and 100 mg/kg), Pb (20, 100, and 400 mg/kg), and their different concentration combinations. A suite of biomarkers, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), metallothionein (MT), malondialdehyde (MDA), and acetylcholinesterase (AChE), were measured after 7, 14, 21, and 28 days of exposure to evaluate their oxidative stress status. Cell apoptosis of soft tissue was also determined after exposure. Results revealed that these endpoints represented sensitive biomarkers for the characterization of the oxidative stress response induced by these metals. Specifically, a decrease of SOD and GPx and an increase of MDA were indicative of the potential failure of the antioxidant defense system in neutralizing the reactive oxygen species (ROS) generated in the exposure of the Pb-treated group. The integrated biomarker response (IBR) index revealed the most significant sub-lethal toxicity for Pb-spiked sediments, leading to the highest rate of cell apoptosis (70.8%). Exposure to Cd resulted in a time- and dose-dependent effect on MT levels, which suggested active detoxification of this metal. Exposure to the mixture resulted in amelioration of Pb toxicity, likely due to the competitive binding of Cd to active enzyme, with the result of an observed antagonistic interaction. This study indicated that B. aeruginosa represents a good biomonitor for assessing Cd and Pb contamination of sediments, and laid the foundation for their potential risk assessments in freshwater ecosystems.

Priority Pollutants in Water and Sediments of a River for Control Basing on Benthic Macroinvertebrate Community Structure

Understanding the drivers of macroinvertebrate community structure is fundamental for adequately controlling pollutants and managing ecosystems under global change. In this study, the abundance and diversity of benthic macroinvertebrates, as well as their chemical parameters, were investigated quarterly from August 2014 to April 2015 in four reaches of the Huai River basin (HRB). The self-organizing map (SOM) algorithm and canonical correspondence analysis (CCA) were simultaneously applied to identify the main factors structuring the benthic community. The results showed that the benthic community structure was always dominated by gastropoda and insecta over seasons and presented obvious spatial and temporal heterogeneity along different pollution levels. The insects were always the top contributors to number density of the benthic community, except for the summer, and the biomass was mainly characterized by mollusca in all seasons. Statistical analysis indicated that TN and NH3-N in water, as well as Hg, As, Cd, and Zn in sediments, were the dominant factors structuring the community, which determined the importance of sediment heavy metal concentrations in explaining the benthic community composition in comparison with other factors. These major factors should be given priority in the process of river pollutant control, which might be rated as a promising way to scientifically improve river health management and ecological restoration.

Impact of environmental factors on aquatic biodiversity in roadside stormwater ponds

Constructed stormwater ponds mitigate runoff volumes and pollution, and provide other ecosystem services, such as supporting biodiversity, but these services attracted relatively less attention. The impacts of the pollution levels in the water column and sediments, the physical characteristics of ponds, and the presence of amphibians on the macroinvertebrate community composition and biodiversity were explored in twelve stormwater ponds in Norway. Also, the similarities between macroinvertebrate, zooplankton and plant communities were explored. Most of the taxa displayed in the ordination diagram were positively correlated with the pond size and the number of neighbouring ponds, and negatively correlated with the pollution levels in the water column and sediments. However, no statistically significant impacts on the number of taxa and Shannon index were observed. There were low similarities between the macroinvertebrate and zooplankton community compositions as well as between the plant and macroinvertebrate community compositions in the stormwater ponds. We observed a significant positive correlation between the number of plant and of zooplankton taxa, and a weak non-significant positive correlation between the number of plant and of macroinvertebrate taxa. Overall, the explanatory variables had a significant impact on the community composition, but not on the number of taxa nor Shannon index.

Species Diversity Hinders Adaptation to Toxicants

Environmental toxicants such as pesticides exert strong selection pressure on many species. While the resulting development of pesticide resistance in agricultural pest species is well-known, reports on the extent of adaptation in exposed nontarget species are contradictory. These contradictory reports highlight a continuing challenge in understanding the relevant ecological mechanisms that facilitate or hinder adaptation to toxicants in the field. Here we show that species diversity hinders the adaptation to toxicants. In agricultural streams with low diversity, we observed an up to 8-fold increase in insecticide tolerance in a total of 17 macroinvertebrate species that was not observed in more diverse communities under similar contamination. High species diversity occurred independently from adjacent nonpolluted refuge areas. Therefore, the low level of adaptation in diverse streams cannot be explained by an increased recolonization of sensitive individuals from refuge areas. Instead, high intraspecific competition may facilitate the selection for increased tolerance in low-diverse communities. In diverse communities, by contrast, species interactions may reduce intraspecific competition and, thus, the potential for developing toxicant resistance. We suggest that this mechanism may be the general case in adaptation to environmental stressors. Additionally, we conclude that the current framework for risk assessment of pesticides is not protective against selection for tolerant organisms and the associated risk of genetic erosion.

Biotic interactions govern genetic adaptation to toxicants

The genetic recovery of resistant populations released from pesticide exposure is accelerated by the presence of environmental stressors. By contrast, the relevance of environmental stressors for the spread of resistance during pesticide exposure has not been studied. Moreover, the consequences of interactions between different stressors have not been considered. Here we show that stress through intraspecific competition accelerates microevolution, because it enhances fitness differences between adapted and non-adapted individuals. By contrast, stress through interspecific competition or predation reduces intraspecific competition and thereby delays microevolution. This was demonstrated in mosquito populations (Culex quinquefasciatus) that were exposed to the pesticide chlorpyrifos. Non-selective predation through harvesting and interspecific competition with Daphnia magna delayed the selection for individuals carrying the ace-1^R resistance allele. Under non-toxic conditions, susceptible individuals without ace-1^R prevailed. Likewise, predation delayed the reverse adaptation of the populations to a non-toxic environment, while the effect of interspecific competition was not significant. Applying a simulation model, we further identified how microevolution is generally determined by the type and degree of competition and predation. We infer that interactions with other species—especially strong in ecosystems with high biodiversity—can delay the development of pesticide resistance.

Variation in variance means more than mean variations: what does variability tell us about population health status?

In environmental science, the variability of biological responses in natural or laboratory populations is a well known and documented phenomenon. However, while an extensive literature aims to explain and understand the origin of variability, few try to use it as a demonstration of the population's response facing a stress. We propose here a theoretical framework that explores various patterns of variability both within and among populations, and seeks methods useful in bioevaluation methodologies. We also introduce the concept of "ecotoxicological niche" to characterize the ability of a population to endure contamination.