Consumers, secondary

Northern pike (1.93 pg/g) exhibited a significantly higher mean mercury concentration than common carp (1.23 pg/g). This result indicates a biomagnification of mercury from common carp, a larger secondary consumer, to northern pike, a tertiary consumer. Nevertheless, barbel (1.98 pg/g), also a secondary consumer, showed a mean THg level similar to that of northern pike. Different behavioral habits may explain the high mercury levels found in barbel species. 

We humans eat at all trophic levels. When we eat such things as fruits, vegetables, or the grains shown in Figure 15-2, we are primary consumers when we eat beef or other meat from herbivores, we are secondary consumers. When we eat fish like trout or salmon, which eat insects and other small animals, we are tertiary or quaternary consumers. Our great and growing numbers, however, are possible only because of our ability to ear as primary consumers. 

Filter feeder- and carnivore- related constants were calculated from the literature but they were altered whilst tuning the model (see Wickens and Field, 1985 for details). The final tuning was done on the carnivore mortality rate. In addition, the standing stocks of the filter-feeders and carnivores were initiated to values i) below and ii) above their calculated values, in a closed system with no water transport, and tuned to reach their original values after several years. Thus the model is tuned to maintain stability of the primary and secondary consumers in a closed system. The model was programmed in GBASIC for an Apple II Computer. 

Secondary consumer Cnidarian testb Hydra attenuata assay Acute lethality (after a 96-h exposure) Blaise and Kusui, 1997... 

For both the Saint-Lawrence River Action Plan (Costan et al., 1993) and the Toyama Bay Japanese (Kusui and Blaise, 1999) studies, the two suites of bioassays employed represented three trophic levels (decomposers, primary producers and primary or secondary consumers), and sought to measure both acute and chronic toxicity. Toxicity tests were selected on the basis of practical and scientific criteria including low sample volume requirement, sensitivity, simplicity of undertaking the assay, ease in maintaining laboratory cultures, cost-effectiveness, procedural reliability and/or frequency of use internationally. 

Secondary consumer Cnidarian test Hydra attenuata Acute lethality (after a 96-h exposure), LC50 Acute sublethal indicated by morphological changes (after a 96-h exposure), EC50 Blaise and Kusui, 1997 Trottier et al., 1997... 

Owing to possible future restrictions that could preclude the testing of samples with all five toxicity tests, we evaluated the index response with a reduced battery of toxicity tests. The basic rule for the selection of tests in a reduced battery was to maintain one primary producer, one primary consumer and a secondary consumer. The test combinations of two selected reduced batteries were Hydra, Daphnia and Lactuca tests (H-D-L) and Hydra, Daphnia and S. capricornutum (H-D-S) tests... 

Heterotrophic organisms which consume other organisms and/or particulate organic matter. Primary consumers are herbivores (e.g., daphnids eating micro-algae) whereas secondary consumers are carnivores (e.g., hydras eating daphnids). Volume 2(1). 

Extrapolating toxicant effects among media may differ according to the trophic status of the species under consideration. Whether a species is a primary producer, primary consumer, or secondary consumer will influence which environmental compartments and media, and hence which routes of uptake, need to be considered. 

All other organisms, which are heterotrophs, must consume organic material made by autotrophs in order to obtain energy and nutrients. In this way they may eat plants (herbivores) or animals (carnivores), or decompose the remains of other organisms and their waste products (decomposers). Herbivores are primary consumers, carnivores are secondary consumers, or they may be tertiary consumers if they eat other consumers. 

Despite their complexity, food webs basically follow a series of steps or levels—from producers to primary consumers, to secondary consumers, and so on. These feeding levels are called trophic levels. All producers belong to the first trophic level all primary consumers belong to the second trophic level, and so on. All feeding relationships can be visualized as a flow of nutrients and energy through a series of trophic levels. There are no more than three or four discernible trophic levels in any ecosystem. 

The concept of user and ultimate consumer is especially important to the archivist and accounts for one of the most serious problems. The user, or primary consumer, buys the paper and makes the record. The ultimate consumer, or secondary consumer (the archivist), acquires the record and must live with the quality of the record received. Thus, the archivist is in a unique position of helplessness with respect to the quality of the materials on which the records are made. The librarian shares this unfortunate dilemma with the archivist. 

The processes which contribute to transfers of nutrients among different pools in a natural ecosystem include uptake by plants, transfer to primary and secondary consumers, return to the organic and inorganic pool in the soil through litter of plant origin and animal excreta and dead bodies, decomposition of roots, rainfall, and fixation of... 

On the next level upward in the pelagic food web are the primary consumers, the zooplankton (microscopic animals). They feed on phytoplankton and, in turn, become food for larger animals (secondary consumers) such as sardines, herring, tuna, bonito, and other kinds of fish and swimming mammals. At the top of this food web are the ultimate consumers, the toothed whales. (A baleen whale s diet consists mostly of plankton). 

Verity and Smetacek (1996) have argued that predation or top-down trophic effects are as important as resource-driven or bottom-up factors in structuring planktonic ecosystems. However, grazing control of phytoplankton floristic composition will only occur if secondary consumers are selective for particular algal types. Initial evidence was against such selection. Marshall (1973) reviewed the evidence for dietary restriction in copepods ... 

Acute toxicity and short-term bioaccumulation. Studies of acute toxicity measure the lethal response after 24 or 96 h of exposure in various bodies of water. Test species should be chosen from amongst most commonly used organisms and standardized procedures should be applied. The test should include at least three different trophic levels, namely primary producers, primary consumers and secondary consumers. Normally, organisms such as green algae, daphnids and fish are utilized. 

Chemicals may affect both the function and the structure of the biotic section of an ecosystem. In this respect, the ecologically functional distinction between producers, consumers, and decomposers is important when considering environmental hazards. In the OECD guidelines, green algae is selected as a producer, Daphnia as primary consumer, and fish as secondary consumer. In ecological risk assessments, the minimum data set at the acute or chronic level should be 3 studies on at least 2 taxonomic groups, while at the ecosystem level one carefully conducted study on an appropriate species or communities should be sufficient. 

Concentration factors for metals within organisms and the retention of stable metal species within ecosystems both contribute to the transfer of metals along food chains and the toxic effects. Thus, primary producers can accumulate high concentrations, and these are consumed by organisms on secondary trophic levels in the food chain. If the food type of the secondary consumer contains biochemically reactive metals, they will be absorbed and accumulated however, if they are insoluble they will pass through the gut and be excreted in the feces. 

Secondary consumers eat the primary consumers and produce feces waste, biomass, and cellular respiratory products. Respiration totally degrades the biomass, usually producing water and carbon dioxide. These compounds cannot be further exploited for their energy values and so are the ultimate energy sink for an ecosystem. 

Vertebrates Birds (e.g., Sturms spp.) Small mammals (e.g., Rattus spp.) Integrate air and food chain sources of exposure often good accumulators of lipophilic pollutants Generally abundant and often resistant to toxic effects include both primary and secondary consumers... 

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