Trophic position

Recognition among bone-chemistry researchers that strontium enters bone in proportion to dietary levels has resulted in widely accepted yet erroneous inferences about the relationships among various elements in bone and past diet. One such inference is that more of any element in the diet translates directly to more of that element in bone. If an element is not biogenically incorporated within bone, or if biological levels are metabolically controlled, then that element will not reflect diet. A second erroneous inference is that strontium can be used to measure the dietary plant/meat ratio. Sr/Ca ratios in meat are generally lower than those of plants, but meat is also low in calcium and hence has little effect on the composition of bone. Plants, on the other hand, contribute substantially to bone composition. Variations in the strontium levels of bone thus more likely reflect differential consumption of plants rather than trophic position. Although efforts to determine plant/meat ratios from strontium and to draw dietary inferences from elements other than strontium and barium have not been successful, this failure has been due to inappropriate expectations, not to a failure of bone strontium to reflect diet. 

Cost concerns (here, High implies there are substantial costs associated with the indicator) Spatio-temporal variation in trophic position can confound and complicate interpretation of trends in mercury concentration in the indicator Low Medium Medium Medium to High Low, if done every 5—10 years Low Medium... 

Peech Cherewyk 2002 Tsui and Wang 2004). Phytoplankton have a constrained trophic position are not consumed by fish, wildlife, or humans, and are indirectly relevant to the pnbhc or the policy commnnity. They wonld respond veiy rapidly — within minntes or honrs — to changes in MeHg concentrations in water. Phytoplankton obtain MeHg directly from water (Mason et al. 1996), and algal density can inlinence concentrations of MeHg in phytoplankton via biomass dilntion (Pickhardt et al. 2002). 

Barium is an alkaline-earth metal incorporated into bone through the intestinal tract. In terrestrial environments, barium and strontium are approximately equal in abundance. In marine environments, barium forms an insoluble precipitate as a result of the high sulfate content in salt water. Formation of this compound effectively removes barium from seawater. As a result, Ba/Sr ratios reflect diet and are an indicator of trophic position. In human populations, individuals with diets high in marine-based food resources typically have low Ba/Sr ratios in their bone and teeth. Populations who consume large amounts of terrestrial-based food resources tend to have higher Ba/Sr ratios. 

Criteria for species selection included abundant availability and trophic position within the mangrove food web. Fish were captured using a traditional cast net. Other organisms were collected directly from their... 

J. Rirby, W. A. Maher, Tissue accumulation and distribution of arsenic compounds in three marine fish species relationship to trophic position, Appl. Organomet. Chem., 16 (2002), 108-115. 

Rolff C, Broman D, Naf C, Zebiihr Y (1993), Chemosphere 27 461-468.. .Potential biomagnification of PCDD/Fs - New possibilities for quantitative assessment using stable isotope trophic position"... 

Alternately, the decomposer organisms can be subdivided by their respective trophic positions. The traditionally well-described food chains of herbivore-carnivore systems for higher animals... 

Kidd, K.A., D.W. Schindler, R.H. Hesslein, and D.C.G. Muir. 1998. Effect of trophic position and lipid on organochlorine concentrations in fishes from subarctic lakes in Yukon Territory. Can. J. Fish. Aquat. Sci. 55 869-881. 

Results of this study have verified and extended the suggestion made in previous radioisotope food chain studies. . . that the shape of the uptake curves [Figure 80b] can be indicative of the trophic position of a population of consumers in the field. Thus, populations known to be strictly herbivorous reach a peak of radioactivity very soon after the primary producers have been labelled, while known predators such as spiders show delayed uptake at lower levels. Intermediate patterns could then be interpreted as indicating feeding from more than one trophic level. 

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