Dynamic energy budget - AbsoluteAstronomy.com

The Dynamic Energy Budget (DEB) theory aims to identify simple quantitative rules for the organization of metabolism

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

of individual organisms that can be understood from basic first principles. The word "dynamic" refers to the life cycle perspective of the theory, where the budget changes dynamically over time.

Cornerstones of the theory are:

conservation of mass
Mass balance
A mass 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 been unknown, or difficult to measure without this technique...

, energy
Energy balance (biology)
In biology, energy balance is the biological homeostasis of energy in living systems. It is measured with the following equation: Energy intake = internal heat produced + external work + storage. It is also an aspect of bioenergetics, concerning energy flow through living systems.It generally uses...

and time,
relationships between surface area and volume
stoichiometric constraints on production
organisational uncoupling of metabolic modules
Modularity (biology)
Many organisms consist of modules, both anatomically and in their metabolism. Anatomical modules are usually segments or organs. When we look at illustrations of metabolic reactions, we find that they, too, are modular: we can clearly identify, for instance, the citric acid cycle as a complex...
strong and weak homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
substrate(s) from the environment is/are first converted to reserve(s) before being used for further metabolism

They are essential to understand evolution of metabolic organisation since the origin of life.

DEB theory delineates reserve

Dynamic reserve

Reserve in the context of the Dynamic Energy Budget theory means the set of metabolites that the organism can use for metabolic purposes. These compounds can have active metabolic functions, however. They are not just "set apart for later use". Reserve differs from structure in the first place by...

s, as separate from structure.
Reserves are synthesized from environmental substrates (food) for use by the metabolism for the purpose of somatic maintenance

Maintenance of an organism

Maintenance of an organism is the collection of processes to stay alive, excluding production processes.The Dynamic Energy Budget theory delineates two classes...

(including protein turnover, maintenance of concentration gradients across membranes, activity and other types of work), growth (increase of structural mass), maturity maintenance

Maintenance of an organism

Maintenance of an organism is the collection of processes to stay alive, excluding production processes.The Dynamic Energy Budget theory delineates two classes...

(installation of regulation systems, preparation for reproduction, maintenance of defense systems, such as the immune system

Immune system

An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...

), maturation

Maturation

Maturation could refer to any of the following:* Fetal development* Developmental biology* Emotional development* Or physical maturation of any biological life form - see individual articles for maturation of different life forms....

(increase of the state of maturity) and reproduction. This organizational position of reserve creates a rather constant internal chemical environment, with only an indirect coupling with the extra-organismal environment. Reserves as well as structure are taken to be generalised compound

Generalised compound

A generalized compound is a mixture of chemical compounds of constant composition, despite possible changes in the total amount. The concept is used in the Dynamic Energy Budget theory, where biomass is partitioned into a limited set of generalised compounds, which contain a high percentage of...

s, i.e. mixtures of a large number of compounds, which do not change in composition. The latter requirement is called the strong homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

assumption. Polymers (carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

s, protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s, ribosomal RNA

Ribosomal RNA

Ribosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...

) and lipid

Lipid

Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s form the main bulk of reserves and of structure.

Some reasons for including reserve

Dynamic reserve

are to give an explanation for:

the metabolic memory; changes in food (substrate) availability affect production (growth or reproduction) with some delay. Growth continues for some time during starvation
Starvation
Starvation is a severe deficiency in caloric energy, nutrient and vitamin intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death...

; embryo development is fueled by reserves
the composition of biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

depends on growth rate. With two components (reserves and structure) particular changes in composition can be captured. More complex changes require several reserves, as is required for autotroph
Autotroph
An autotroph, or producer, is an organism that produces complex organic compounds from simple inorganic molecules using energy from light or inorganic chemical reactions . They are the producers in a food chain, such as plants on land or algae in water...

s.
the body size scaling of life history parameters. The specific respiration rate decreases with (maximum) body size between species because large bodied species have relatively more reserve. Many other life history parameters directly or indirectly relate to respiration.
the observed respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...

patterns, which reflect the use of energy. Freshly laid eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

hardly respire, but their respiratory rate
Respiratory rate
Respiratory rate is also known by respiration rate, pulmonary ventilation rate, ventilation rate, or breathing frequency is the number of breaths taken within a set amount of time, typically 60 seconds....

s increase during development while egg weight decreases. After hatching, however, the respiration rate further increases, while the weight now also increases
all mass fluxes are linear combinations of assimilation, dissipation and growth. If reserves are omitted, there is not enough flexibility to capture product formation and explain indirect calorimetry
Calorimetry
Calorimetry is the science of measuring the heat of chemical reactions or physical changes. Calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning heat...

.

The standard model quantifies the metabolism of isomorph

Isomorph

An isomorph is an organism that does not change in shape during growth. The implication is that its volume is proportional to its cubed length, and its surface area to its squared length...

s with 1 reserve and 1 structure that feeds on one type of food with a constant composition. The rules for the standard model for reproducing multicellulars, and modified for dividing unicellulars, are:

Assumptions of the standard model

The state variables of the individual are structural mass and reserve; they have a constant composition (strong homeostasis).

Food is transformed into reserve, which fuels all other metabolic processes

The reserve density at birth equals that of the mother at egg formation. Foetuses develop similarly, but receive unrestricted amount of reserve from the mother during development.

Stage transitions occur if the cumulated investment into maturation

Maturation

exceeds threshold values. These stages typically are: embryo, juvenile and adult.

Somatic maintenance is proportional to structural body volume, and maturity maintenance to maturity but maturity does not increase in the adult stage. Heating costs for endotherms and osmostic work (for fresh water organsism) are somatic maintenance costs that are proportional to surface area.

The feeding rate is proportional to the surface area; food handling time and the transformation efficiency from food to reserve are independent of food density.

The reserves is such that weak homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

applies: the chemical composition of the body becomes constant during growth in a constant environment.

A fixed fraction (called kappa) of mobilized reserve is allocated to somatic maintenance plus growth (soma), the rest on maturity maintenance plus maturation or reproduction.

Reserve that is allocated to reproduction is first accumulated in a buffer. The rules for converting the buffer to gametes are species-specific (e.g. spawning can be once per season).

During starvation, individuals always give priority to maintenance. After having used the reproduction buffer, they allow a species-specific amount of shrinking of structure and/or maturity

These assumptions quantify all energy and mass fluxes in an organism (including heat

Heat

In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

, dioxygen, carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

) and imply rules for the covariation of parameter values across species (body size scaling relationships).

Extensions of the standard model

DEB theory has been extended into many directions, such as

effects of changes in shape during growth (e.g. V1-morph
V1-morph
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 1, so to its volume...

s and V0-morph
V0-morph
An V0-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume to the power 0, so its surface area is constant....

s)
inclusion of more types of food (substrate), which requires Synthesizing Unit
Synthesizing Unit
Synthesizing Units are generalized enzymes that follow the rules of classic enzyme kinetics with two modifications:*product formation is not taken to be a function of substrate concentrations but of substrate fluxes that arrive at the SUs...

s to model
inclusion of more reserves (which is necessary for organisms that do not feed on other organisms) and more structures (which is necessary to deal with plants)
the formation and excretion of metabolic products (which is a basis for syntrophic
Syntrophy
Syntrophy, Cross-feeding, or Cross feeding is the phenomenon that one species lives off the products of another species.For example house dust mites live off human skin flakes, of which a healthy human being produces about 1 gram per day...

relationships, and useful in biotechnology
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...

)
the production of free radicals (linked to size and nutritional status) and their effect on survival (aging)
the growth of body parts (including tumours)
effects of chemical compounds (toxicant
Toxicant
A toxicant is a chemical compound that has an effect on organisms.A distinction can be drawn between "toxic" and toxin, with the latter being a subcategory of the former....

s) on parameter values and the hazard rate (which is useful to establish no effect concentration
No effect concentration
Measures of pollutant concentration are used to determine risk assessment in public health.Industry is continually synthesizing new chemicals, the regulation of which requires evaluation of the potential danger for human health and the environment...

s for environmental risk assessment
Risk assessment
Risk assessment is a step in a risk management procedure. Risk assessment is the determination of quantitative or qualitative value of risk related to a concrete situation and a recognized threat...

): the DEBtox
DEBtox
The DEBtox method for the evaluation of effects of toxicants makes use of the Dynamic Energy Budget theory to quantify the effect. See the Organisation for Economic Co-operation and Development report, below, for a description of the method....

method
processes of adaptation (gene expression) to the availability of substrates (important in biodegradation
Biodegradation
Biodegradation or biotic degradation or biotic decomposition is the chemical dissolution of materials by bacteria or other biological means...

)

DEB theory provides constraints on the metabolic organisation of sub-cellular processes. Together with rules for interaction between individuals (competition, syntrophy

Syntrophy

Syntrophy, Cross-feeding, or Cross feeding is the phenomenon that one species lives off the products of another species.For example house dust mites live off human skin flakes, of which a healthy human being produces about 1 gram per day...

, prey-predator relationships), it also provides a basis to understand population and ecosystem dynamics. The theory, therefore, links various levels of biological organisation (cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s, organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s and population

Population

A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

s). A considerable number of popular empirical models turn out to be special cases of the DEB model, or very close numerical approximations.

Dynamic energy budget theory and body size

The explanation of certain body size relationships differs for intra- and inter-species comparisons in the context of the Dynamic Energy Budget (DEB) theory. Young (small) organisms behave different from old (large) ones of the same species because they typically do different things (grow fast and don't reproduce). Adults of small-bodied species, however, are expected to behave similarly to adults of large-bodied species. The reason the parameters of the DEB theory vary between species may thus follow naturally from the structure of the theory.

Maximum body length equals the maximum surface area-specific assimilation rate times the fraction of mobilised reserve that is allocated to the soma divided by the volume-specific somatic maintenance costs. Only the first of these three parameters depend on the size of the individual and is, therefore, proportional to maximum length. Appropriate ratios of parameters that depend on size are independent of size; this reveals how such parameters depend on size. Any eco-physiological quantity that can be written as function of DEB parameters can, for this reason, also be written as function of the maximum body size.

Assumptions of the standard model

Extensions of the standard model

Dynamic energy budget theory and body size

See also