Stoichiometry: Linking Elements to Biochemicals

Abstract

Abstract. Ecological stoichiometry is a useful tool for studying how the elemental composition of organisms and their food affects production, nutrient cycling, and foodweb dynamics. Two analyses are presented here that show that the use of simple element ratios in stoichiometric calculations may in certain circumstances prove inadequate because of the influence in animal nutrition of biochemical aspects of diet. In the first, a stoichiometric analysis of herbivores consuming food with varying carbon to nitrogen (C:N) ratios is undertaken, in which the intake of C is segregated into easily assimilated compounds and fiber. Two herbivore strategies emerge from the analysis, both as a means of minimizing limitation by C, not N: fiber eaters that consume high C:N food and have efficient fiber digestion, and selective feeders that consume low C:N food but that do not possess fiberdigesting enzymes. In the second example, the stoichiometric axiom that a single substrate, the one in least supply relative to demand, limits growth is used to identify potentially limiting essential amino acids in the diets of a range of animals. Large consumer-prey imbalances in amino acids were found in several cases, indicating that, at least in theory, growth should be strongly limited by individual amino acids rather than bulk N. In practice such limitation may be offset in consumers by physiological and other factors such as symbiotic relationships. The two analyses emphasize the simplicity of element stoichiometry, highlighting the need to consider biochemical and physiological arguments when undertaking stoichiometric studies of carbon and nutrient transfers in ecosystems.

Optimal Foraging for Multiple Resources in Several Food Species

“…This model enables the prediction of the optimal combination of food species in a method that is complementary to the work of explicitly defining a multidimensional fitness landscape Simpson et al 2004) or considering independent fitness effects of surpluses or deficits in separate resources (Anderson et al 2004;Raubenheimer and Simpson 2004;Simpson et al 2004). Our model can be tested using field experiments.…”

“…During these short foraging bouts, herbivores need to acquire enough of all resources to have the time to engage in nonforaging activities, such as vigilance and searching for mates. In food species, the ratio between the concentrations of resources will, in most cases, be different from the ratio of the turnover rates of these resources in the herbivore (Prins and Beekman 1989;Anderson et al 2004;Prins and van Langevelde 2008). An herbivore thus faces the twofold problem of having to choose between different food species in order to balance the intake of several resources to its requirements and of having to maximize the rate at which this optimal food mix is consumed.…”

Widespread natural intraspecific variation in tissue stoichiometry of two freshwater molluscs: Effect of nutrient enrichment

“…This result was not surprising. Such intraspecific differences in C, N, and P contents may link to differences in the body content of biomolecules among individuals (Anderson et al, 2004;Vrede et al, 2004). C:N:P ratios differences likely reflect, in part, the relative contribution of rRNA (P-rich) and structural molecules (C-and N-rich) to tissue composition.…”

Biological Stoichiometry: The Elements at the Heart of Biological Interactions

“…Moreover, it was shown that the quantity of resources, besides their stoichiometric compositions, affects the gross growth efficiencies of elements . Furthermore, models that included a description of the distribution of elements among the various biomolecules in cells have shown that it is not even always possible to set one element as the growth-limiting factor (Anderson et al 2004). It thus became clear that more physiologically grounded models of the use of elements by organisms were needed.…”