Abundance Of Trophic Levels Research Articles

Deriving aquatic PNECs of endocrine disruption effects for PFOS and PFOA by combining species sensitivity weighted distributions and adverse outcome pathway networks

Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), as emerging endocrine-disrupting chemicals (EDCs), pose adverse effects on aquatic organisms. Conventional ecological risk assessment (ERA) not fully considering the mode of toxicity action of PFOS and PFOA, may result in an underestimation of risks and confuse decision-makers. In the study, we developed species sensitivity weighted distribution (SSWD) models based on adverse outcome pathway (AOP) networks for deriving predicted no-effect concentrations (PNECs). Three kinds of weighting criteria (intraspecies variation, trophic level abundance, and data quality) and weighted log-normal distribution methods were adopted. The developed models considered the inter/intraspecies variation and integrated nontraditional endpoints of endocrine-disrupting effects. The PNECs of endocrine disruption effects were derived as 2.52 μg/L (95% confidence intervals 0.667–9.85 μg/L) for PFOS and 18.7 μg/L (5.40–71.0 μg/L) for PFOA, which were more conservative than those derived from the SSD method and were comparable with the values in the literature based on the chronic toxicity data. For PFOS, the effect of growth and development was the most sensitive; however, for PFOA, the effect of reproduction was the most sensitive in the effects of growth and development, reproduction, biochemistry and genetics, and survival. The endocrine-disrupting effects of PFOS and PFOA are significant and need to be fully recognized in the ERA. This study provided an ERA framework that can improve the ecological relevance and reduce the uncertainty of PNECs of EDCs.

Effects of selective fishing on a small scale multi-species and multi-gear freshwater fishery in the Magdalena River Basin (Colombia)

Classical management has not been able to stop the 65% decrease in fishery production during the last 40 years in the Magdalena–Cauca River Basin. To analyze the effects of selective fishing of multiple species and small scale fisheries we addressed temporal changes at fishing level and the response of fishermen. The fishery reduced production and CPUE (catch per unit effort standardized), decreased the large sizes and growth rates of Prochilodus magdalenae and Pseudoplatystoma magdaleniatum, changed the abundance of trophic levels (decreased carnivores and increase of detritivores, omnivores), and increased exploitation rates. The fishermen have responded by implementing self-control measures, diversifying fishing gear and mesh size, including new species and sizes in the catch with a higher CPUE of small sized fish, adjusting the fishing effort to the abundance. We conclude that selective fishing has had ecological effects and fishermen have empirically self-regulated to optimize the cost–benefit ratio of their activity, developing a fishery that is more in line with ecosystemic structures. We address the balanced harvest strategy as a management alternative.

Long‐term empirical evidence, early warning signals and multiple drivers of regime shifts in a lake ecosystem

Abstract Catastrophic regime shifts in various ecosystems are increasing with the intensification of anthropogenic pressures. Understanding and predicting critical transitions are thus a key challenge in ecology. Previous studies have mainly focused on single environmental drivers (e.g. eutrophication) and early warning signals (EWSs) prior to population collapse. However, how multiple environmental stressors interact to shape ecological behaviour and whether EWSs were detectable prior to the recovery process in lake ecosystems are largely unknown. We present long‐term empirical evidence of the critical transition and hysteresis with the combined pressures of climate warming, eutrophication and trophic cascade effects by fish stocking in a subtropical Chinese lake in the Yangtze floodplain. The catastrophic regime shifts are cross‐validated by 64‐year multi‐trophic level monitoring data and paleo‐diatom records. We show that EWSs are detectable in both the collapse and recovery trajectories and that including body size information in composite EWSs requires shorter time‐series data and can improve the predictive ability of regime shifts. Although full recovery has not yet been observed, EWSs prior to recovery provide us with the opportunity to take measures for a clear‐water regime. Climate warming and top‐down cascade effects have a negative influence on water clarity by altering lower trophic level abundance and body size, which, in turn, have a negative effect on macrophyte abundance. Furthermore, we identify a shift in the dominant driving forces from bottom‐up to top‐down after regime shifts, decoupling the relationships between nutrients and biological components and thus decreasing the efficiency of nutrient reduction. Synthesis. This study provides new insights into ecological hysteresis under multiple external stressors and improves our understanding of trait‐based early warning signals in both the collapse and recovery processes in natural freshwater ecosystems. For management practice, our work suggests that slowing down climate warming and weakening the fish predation pressure on food webs are necessary to increase the effectiveness of nutrient reduction in the restoration of lakes.

Comparison of species sensitivity distribution modeling approaches for environmental risk assessment of nanomaterials – A case study for silver and titanium dioxide representative materials

Species sensitivity distributions (SSDs) are used in chemical safety assessments to derive predicted-no-effect-concentrations (PNECs) for substances with a sufficient amount of relevant and reliable ecotoxicity data available. For engineered nanomaterials (ENMs), ecotoxicity data are often compromised by poor reproducibility and the lack of nano-specific characterization needed describe an ENM under test exposure conditions. This may influence the outcome of SSD modelling and hence the regulatory decision-making. This study investigates how the outcome of SSD modelling is influenced by: 1) Selecting input data based on the nano-specific “nanoCRED” reliability criteria, 2) Direct SSD modelling avoiding extrapolation of data by including long-term/chronic NOECs only, and 3) Weighting data according to their nano-specific quality, the number of data available for each species, and the trophic level abundance in the ecosystem. Endpoints from freshwater ecotoxicity studies were collected for the representative nanomaterials NM-300 K (silver) and NM-105 (titanium dioxide), evaluated for regulatory reliability and scored according to the level of nano-specific characterization conducted. The compiled datasets are unique in exclusively dealing with representative ENMs showing minimal batch-to-batch variation. The majority of studies were evaluated as regulatory reliable, while the degree of nano-specific characterization varied greatly. The datasets for NM-300 K and NM-105 were used as input to the nano-weighted n-SSWD model, the probabilistic PSSD+, and the conventional SSD Generator by the US EPA. The conventional SSD generally yielded the most conservative, but least precise HC5 values, with 95 % confidence intervals up to 100-fold wider than the other models. The inclusion of regulatory reliable data only, had little effect on the HC5 generated by the conventional SSD and the PSSD+, whereas the n-SSWD estimated different HC5 values based on data segregated according to reliability, especially for NM-105. The n-SSWD weighting of data significantly affected the estimated HC5 values, however in different ways for the sub-datasets of NM-300 K and NM-105. For NM-300 K, the inclusion of NOECs only in the weighted n-SSWD yielded the most conservative HC5 of all datasets and models (a HC5 based on NOECs only could not be estimated for NM-105, due to limited number of data). Overall, the estimated HC5 values of all models are within a relatively limited concentration range of 25−100 ng Ag/L for NM-300 K and 1−15 μgTiO2/L for NM-105.

Species sensitivity weighted distribution for ecological risk assessment of engineered nanomaterials: the n-TiO2 case study.

Societal concerns about the environmental risks of engineered nanomaterials (ENMs) have recently increased, but nano-ecological risk assessments are constrained by significant gaps in basic information on long-term effects and exposures, for example. An approach to the ecological risk assessment of ENMs is proposed that can operate in the context of high uncertainty. This approach further develops species sensitivity weighted distribution (SSWD) by including 3 weighting criteria (species relevance, trophic level abundance, and nanotoxicity data quality) to address nano-specific needs (n-SSWD). The application of n-SSWD is illustrated for nanoscale titanium dioxide (n-TiO2 ), which is available in different crystal forms; it was selected because of its widespread use in consumer products (e.g., cosmetics) and the ample availability of data from ecotoxicological studies in the literature (including endpoints for algae, invertebrates, bacteria, and vertebrates in freshwater, saltwater, and terrestrial compartments). The n-SSWD application resulted in estimation of environmental quality criteria (hazard concentration affecting 5% and 50% of the species) and ecological risk (potentially affected fraction of species), which were then compared with similar results obtained by applying the traditional species sensitivity distribution (SSD) approach to the same dataset. The n-SSWDs were also built for specific trophic levels (e.g., primary producers) and taxonomic groups (e.g., algae), which helped to identify the most sensitive organisms. These results showd that n-SSWD is a valuable risk tool, although further testing is suggested.

Interactive Effects of Disturbance, Productivity, and Consumer Diversity on the Structure of Prey Communities

Experiments show that consumer diversity can have important effects on the control of prey diversity and abundance. However, theory also indicates that the strength of consumer effects on such properties will vary depending on system productivity and disturbance regime. Using a laboratory-based system composed of ciliate consumers and bacterial prey, I explored the interactive effects of productivity, disturbance, and consumer diversity on prey diversity and trophic-level abundance. Consumer diversity had productivity-dependent effects on bacterial prey that were consistent with theoretical expectations. At low productivity, increasing consumer diversity reduced prey abundance while at high productivity no effects were detected due to compensatory responses among bacteria. In contrast, consumer diversity had weak effects on prey diversity at low productivity but significantly depressed prey diversity at high productivity. Disturbance on consumers enhanced prey diversity but did not alter consumer diversity effects on prey. These results indicate that consumer diversity may play an important role in the regulation of prey communities, but the strength of this effect varies with system productivity.

Metabolism Predicts Ecological Response to Warming

Metabolism Predicts Ecological Response to Warming

Spatial patterns in fish biomass and relative trophic level abundance in a wastewater enriched river

Abstract – It is generally accepted that nutrient enrichment of aquatic systems will lead to increased production at the top trophic level (fish). We found that in the wastewater enriched Bow River, Alberta rainbow trout (Oncorhynchus mykiss) biomass increased over 25‐fold, and brown trout (Salmo trutta) biomass increased 5‐fold, however total sportfish biomass did not increase below the nutrient input point source. This was due to a dramatic downstream decrease in mountain whitefish (Prosopium williamsoni) biomass to 2% of the average biomass upstream of the municipal effluent source. The spatial pattern over a 177‐km river section encompassing the city of Calgary, showed that the increase in trout abundance approximately tracked the expected nutrient concentrations in the river, but with a downstream lag of 20–30 km. Mountain whitefish biomass over the 177 km was inversely related to the dominant trout species, rainbow trout. Invertebrate abundance, macrophyte biomass and phytoplankton biomass all increased below the wastewater treatment plant outfalls. However, periphyton data were highly variable and showed no response. We propose several hypotheses as regards the factors that may have led to the decrease in mountain whitefish, based on the data from all trophic levels and the spatial pattern for fish biomass. Proposed factors influencing the mountain whitefish decline were; altered competitive ability because of macrophyte abundance, ammonia toxicity and barriers to movement (weirs).

Mapping nitrate in the global ocean using remotely sensed sea surface temperature

Nitrogen is the most broadly limiting factor for marine phytoplankton on ecological timescales. Nitrate, as the most oxidized inorganic species, plays a significant role in nitrogen availability based on nutrient flux to the euphotic zone from deeper waters, and is a major determinant of new production. Increased new production relates to higher trophic level abundance and to carbon dioxide drawdown from the atmosphere. The present work is the first stage in the development of a technique to generate a scaled index of nitrate availability in the surface waters of the global ocean using satellite‐derived temperature data. The technique currently involves a fixed matrix of nitrate depletion temperatures (NDT) and remotely‐sensed sea surface temperature (SST) from the monthly‐averaged AVHRR Pathfinder series. The magnitude of the difference between these two temperatures at a given location indicates the degree of nitrate presence or absence. Graded monthly nitrate presence/absence maps over a 10‐year period were created based on the size of the difference between these two temperatures. A 10‐year average of these differences exhibits major nitrate distribution features similar to those observed in maps based on National Oceanic Data Center archived measurements. In contrast, monthly nitrate maps provide a unique and dynamic representation of nitrate availability in the global ocean. This nutrient monitoring capability based on remotely sensed data can contribute to the estimation of new production in the global ocean, improving management of various world fisheries and improving estimation of the atmospheric draw down of carbon dioxide, a major greenhouse gas.

Influence of salmon spawner densities on stream productivity in Southeast Alaska

We conducted this study to determine the relationship between salmon spawner abundance and stream biofilm and benthic macroinvertebrate abundance in Southeast Alaska. Experiments took place in outdoor artificial and natural streams. Six pink salmon (Oncorhynchus gorbuscha) carcass treatments (0.00, 1.45, 2.90, 4.35, 5.80, and 7.25 kg wet mass) placed in artificial channels were subsampled repeatedly for biofilm ash-free dry mass (AFDM), chlorophyll a, and macroinvertebrates. In a small (nonanadromous) forest stream, we sampled benthos throughout a 66-m reach 17 days after distributing 60 carcasses along the lower half of that reach. All response variables significantly increased in response to carcass additions in both artificial and natural streams. Chlorophyll a continued to increase across all loading rates, while AFDM and total macroinvertebrate densities showed no further response to loading beyond the first treatment (1.45 kg) in artificial streams. In the natural stream, AFDM and chironomid densities continued increasing across loading levels. These results indicated that increased spawner densities increased lower trophic level abundance until a trophic capacity was reached. Salmon escapement goals should consider food web effects, especially on trophic levels that support juvenile salmonids, that ultimately affect freshwater salmon production.

The Fallacies of "Ratio‐Dependent" Predation

It has recently been claimed that the functional response of predators depends on the numbers of prey and predators only via their ratio. Contrary to this claim, I argue that such “ratio—dependent” functional responses are very unlikely to occur on theoretical grounds and have not been shown empirically. Previous justifications for ratio—dependent functional responses ignore the role of these responses in determining prey population dynamics. Patterns in the abundances of trophic levels and experimental results that have been cited as support for “ratio—dependent” predation are consistent with numerous other explanations. These other explanation do not suffer from the pathological behaviors and lack of a plausible mechanism that afflict ratio—dependent models. Furthermore, ratio—dependent functional responses, because of their lack of mechanistic basis, do not provide a good basis for developing more detailed models. Nor can the use of ratio—dependent models be justified as a limiting case of more general predator—dependent models.

The responses of unstable food chains to enrichment

This article investigates the mean abundances of trophic levels in simple models of two- and three-level food chains as a function of the rate of input of nutrients. The analysis concentrates on cases in which the equilibrium point with all species present is unstable. In most of the models, the instability arises because the consumer species become satiated when food density is high. In unstable two-level systems, bottom level abundance generally increases with increased nutrient input. The abundance of the second level may decrease with increased input. Changes in the intrinsic rate of increase and carrying capacity of the bottom level can have qualitatively opposite effects on trophic level abundances. Refuges for or immigration of the bottom level usually cause both levels to increase in mean abundance with an increased carrying capacity. A variety of different predator—prey models are discussed briefly and the results suggest that increased nutrient input will often increase the abundance of both levels; however, several circumstances can cause the top level to decrease. In three-level systems, an increased carrying capacity can cause extinction of the top level. Extinction may or may not be conditional on the initial densities of the three levels. These results may help explain the observed lack of correlation between productivity and the number of trophic levels in natural food webs, as well as the lack of very long food chains. The results suggest that patterns of abundances across productivity gradients cannot be used to assess the importance of top-down vs bottom-up effects.

Effect of Increased Productivity on the Abundances of Trophic Levels

Increasing productivity can have a variety of effects on the abundances of higher trophic levels. Previous work, based on models with one type per trophic level, has suggested that increasing nutrient input to the lowest trophic level (1) always increases the abundance of the highest trophic level and (2) increases the abundances of levels that are an even number of levels below the top, while leaving others unchanged. This article investigates how these predic- tions are altered by the presence of different species or types (i.e., heterogeneity) within trophic levels. The models investigated are Lotka-Volterra-type models of food webs with two or three trophic levels and one or two types per level. Less complete results are derived for models with more levels and more types per level. Several different food web structures may cause the highest level to be independent of nutrient input or actually decrease with nutrient input. How- ever, the majority of possible food web configurations with two species on some or all levels can produce productivity-abundance relationships similar to those obtained when trophic levels are homogeneous. Factors other than heterogeneity within levels can affect the productivity- abundance relationships; these factors and available information on relationships in nature are discussed.