Ecological stoichiometry (more broadly referred to as biological stoichiometry) considers how the balance of energy and elements influences living systems. Similar to chemical stoichiometry, ecological stoichiometry is founded on constraints of

mass balance In physics, a mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have ...

as they apply to organisms and their interactions in

ecosystems An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

.R. W. Sterner and J. J. Elser (2002) ''Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere''.

Princeton University Press Princeton University Press is an independent publisher with close connections to Princeton University. Its mission is to disseminate scholarship within academia and society at large. The press was founded by Whitney Darrow, with the financial ...

. pp.584. Specifically, how does the balance of energy and elements affect and how is this balance affected by organisms and their interactions. Concepts of ecological

stoichiometry Stoichiometry () is the relationships between the masses of reactants and Product (chemistry), products before, during, and following chemical reactions. Stoichiometry is based on the law of conservation of mass; the total mass of reactants must ...

have a long history in

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

with early references to the constraints of mass balance made by

Liebig Justus ''Freiherr'' von Liebig (12 May 1803 – 18 April 1873) was a Germans, German scientist who made major contributions to the theory, practice, and pedagogy of chemistry, as well as to agricultural and biology, biological chemistry; he is ...

, Lotka, and Redfield. These earlier concepts have been extended to explicitly link the elemental

physiology Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

s to their

food web A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Position in the food web, or trophic level, is used in ecology to broadly classify organisms as autotrophs or he ...

interactions and ecosystem function. Most work in ecological stoichiometry focuses on the interface between an organism and its resources. This interface, whether it is between plants and their nutrient resources or large

herbivores A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

and

grass Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family (biology), family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and spe ...

es, is often characterized by dramatic differences in the elemental composition of each part. The difference, or mismatch, between the elemental demands of organisms and the elemental composition of resources leads to an elemental imbalance. Consider

termites Termites are a group of detritophagous eusocial cockroaches which consume a variety of decaying plant material, generally in the form of wood, leaf litter, and soil humus. They are distinguished by their moniliform antennae and the sof ...

, which have a tissue

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

ratio (C:N) of about 5 yet consume

wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin t ...

with a C:N

ratio In mathematics, a ratio () shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...

of 300–1000. Ecological stoichiometry primarily asks: # why do elemental imbalances arise in nature? # how is consumer

and

life-history Life history may refer to: * Life history theory Life history theory (LHT) is an analytical frameworkVitzthum, V. (2008). Evolutionary models of women's reproductive functioning. ''Annual Review of Anthropology'', ''37'', 53-73 designed to stud ...

affected by elemental imbalances? and # what are the subsequent effects on ecosystem processes? Elemental imbalances arise for a number of physiological and

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

ary reasons related to the differences in the biological make up of organisms, such as differences in types and amounts of

macromolecule A macromolecule is a "molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass." Polymers are physi ...

organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...

s, and tissues. Organisms differ in the flexibility of their biological make up and therefore in the degree to which organisms can maintain a constant chemical composition in the face of variations in their resources. Variations in resources can be related to the types of needed resources, their relative availability in time and space, and how they are acquired. The ability to maintain internal chemical composition despite changes in the chemical composition and availability of resources is referred to as "stoichiometric homeostasis". Like the general biological notion of

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

, elemental homeostasis refers to the maintenance of elemental composition within some biologically ordered range.

Photoautotrophic Photoautotrophs are organisms that can utilize light energy from sunlight, and elements (such as carbon) from inorganic compounds, to produce organic materials needed to sustain their own metabolism (i.e. autotrophy). Such biological activities ...

organisms, such as

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

and

vascular plants Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue ( ...

, can exhibit a very wide range of physiological plasticity in elemental composition and thus have relatively weak stoichiometric homeostasis. In contrast, other organisms, such as multicellular

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

s, have close to strict homeostasis and they can be thought of as having distinct chemical composition. For example, carbon to

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

ratios in the suspended organic matter in

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

s (i.e.,

, bacteria, and

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

) can vary between 100 and 1000 whereas C:P ratios of ''

Daphnia ''Daphnia'' is a genus of small planktonic crustaceans, in length. ''Daphnia'' are members of the Order (biology), order Anomopoda, and are one of the several small aquatic crustaceans commonly called water fleas because their Saltation (gait), ...

'', a

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

, remain nearly constant at 80:1. The general differences in stoichiometric homeostasis between plants and animals can lead to large and variable elemental imbalances between consumers and resources. Ecological stoichiometry seeks to discover how the chemical content of organisms shapes their ecology. Ecological stoichiometry has been applied to studies of nutrient recycling, resource competition, animal growth, and nutrient limitation patterns in whole ecosystems. The Redfield ratio of the world's oceans is one very famous application of stoichiometric principles to ecology. Ecological stoichiometry also considers phenomena at the sub-cellular level, such as the P-content of a

ribosome Ribosomes () are molecular machine, macromolecular machines, found within all cell (biology), cells, that perform Translation (biology), biological protein synthesis (messenger RNA translation). Ribosomes link amino acids together in the order s ...

, as well as phenomena at the whole biosphere level, such as the oxygen content of

Earth's atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

. To date the research framework of ecological stoichiometry stimulated research in various fields of biology, ecology, biochemistry and human health, including

human microbiome The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding List of human anatomical features, anatomical sites in which they reside, including the human gastrointes ...

research, cancer research, food web interactions, population dynamics,

ecosystem services Ecosystem services are the various benefits that humans derive from Ecosystem, ecosystems. The interconnected Biotic_material, living and Abiotic, non-living components of the natural environment offer benefits such as pollination of crops, clean ...

, productivity of agricultural crops and honeybee nutrition.

Consumer stoichiometry and food webs

The study of elemental ratios (i.e., C:N:P) within the tissues of organisms can be used to understand how organisms respond to changes in resource quality and quantity. For instance, in aquatic ecosystems, nitrogen and phosphorus pollution within streams, often due to agricultural activities, can increase the amount of N and P available to primary producers. This release in the limitation of N and P can impact the abundance, growth rates, and

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

of primary producers within the stream. This change in primary production can trickle through the food web via bottom-up processes and impact the stoichiometry of organisms, limiting elements, and biogeochemical cycling of streams. In addition, bottom-up changes in elemental availability can influence the morphology, phenology, and physiology of organisms that will be discussed below. The focus of this article is on aquatic systems; however, similar processes related to ecological stoichiometry can be applied in the terrestrial environment, as well.

Invertebrate stoichiometry

The demands for carbon, nitrogen and phosphorus at specific ratios by

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

can change at different life stages within invertebrate life history. The growth rate hypothesis (GRH) addresses this phenomenon and states that the demands for phosphorus increase during active growth phases to produce P-rich

nucleic acid Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

s in biomass production and are reflected in the P content of the consumer. During early growth stages, or earlier

instar An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...

s, invertebrates may have higher demands for N and P enriched resources to fuel the ribosomal production of proteins and

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

. At later stages, the demand for particular elements may shift as they are no longer actively growing as rapidly or generating protein rich biomass. Growth rates of invertebrate organisms can also be limited by the resources that are available to them.

References

{{modelling ecosystems, expanded=other Ecology Stoichiometry

Consumer stoichiometry and food webs

Invertebrate stoichiometry

See also

References