Energy budget

Energy balance, and energy balance ( engl. energy budget) called, is in the ecology and ecophysiology of the term for the balance-sheet analysis and display of continuous transformations of energy. It is thus also part of bioenergetics.

Energy balance and energy flow

Energy balances can be measured for an individual organism or a population. While in green plants, the energy needed for metabolism and growth will be included in the form of radiant energy, it is obtained in animals as organically bound energy as part of the food intake. The energy transfer in both cases on growth, progeny production, secretory functions and other energy -requiring processes.

The transfer of energy stored in the organisms in the ecosystem along a food chain or within a food web is referred to as energy flow.

Conceptual Approach

Energy balances are defined for specific periods of time, eg for a second, a day or a year or even over the entire lifetime of the individual. Instead of an energy balance should be correct current account speak ( power = energy unit per time unit). However, the term of the current account has not enforced in this context, probably to bypass the confusion with the analogous terms in energy technology and economics.

The energy units used are those of physical energy ( or work) or service, eg [J] ( joules) or [ kJ ] for energy balances and, for example, [J / s] ( = watts) or [ ( also referred to as rates) kJ / d] for current accounts.

A simplified energy or power balance for humans and animals can be represented as follows:

• C = A E
• A = P R

The following applies:

• C = consumption rate ( = ingestion rate, feeding rate )
• A = assimilation rate ( = rate of absorption in the intestinal system )
• P = production rate ( = growth rate of tissue and rate of production of eggs or embryos )
• R = respiration rate ( = respiration rate )
• E = Egestionsrate ( = Defäkationsrate and excretion )

In addition, where appropriate, by group of animals, further parameters such as the energy levels released into the environment that go through molts (eg insects and snakes) lost. In many animals can also defecation and excretion not differ metrologically readily as the two components are mixed are emitted (birds, insects).

Measurement methods and sample size

In practice, often not directly units of energy are measured, but easily identifiable variables such as fresh mass ( = fresh weight, wet weight), dry matter, ash-free dry mass and mass of organic carbon. In particular, the mass of organic carbon in the food, in the tissue or in the excretion products, by means of a combustion apparatus ( calorimeter ) or can be easily measured by a chemical oxidation reaction, is well correlated with the energy content of the sample in question, so that it a suitable replacement size represents. The respiration rate is usually estimated from the oxygen consumed or carbon dioxide produced. Measurements of animals and plants are carried out experimentally or in combined experimental- field- analytical analyzes.

Example: A person takes in food per day, an energy of 8,000 - to 10,000 kJ, which, however, can vary greatly. In the above formulas, this corresponds to the consumption rate C. It allows a metabolic power of 100 W. Temporary can significantly increase this size, eg to over 200 W at medium or fast walking while dragging a light car and quickly to about 1000 W at maximum physical exertion. This large amount of energy is expended in the form of mechanical work done by the working skeletal muscles, the muscles and the circulatory respiratory movements, and also by the cellular expenses for osmoregulation and molecular transport processes. In all these activities and always heat energy is released automatically, which is a side effect of all energy transformation processes. The total number of hours mechanical, cellular and thermal energy is methodically recorded as Respirationsenergie R; a breakdown of each individual energy components is often difficult.

Ecological Significance

The measurement of energy balances allow fundamental insights into the energy flow in the ecosystem, and thus in the understanding of its energy and material balance. Also in the context of behavioral and evolutionary biology form energy balances important foundations for the theory, since each organism its energy consumption as it either in growth or reproduction or movement activity, etc. can stick to the detriment of the other energy- requiring activities. Here, different strategies have developed in the evolution: Predatory mammals and birds consume relatively large amount of energy for their prey, while crocodiles survive through the principle of Auflauerns with comparatively less energy and can therefore endure long periods of starvation.

Findings on energy balances and their optimization also form the theoretical basis of production calculation in agriculture, animal husbandry and aquaculture. They also constitute an important basis for the calculation of earthly material balances. So give cattle over 6% of its recorded on the food energy ( around 300 liters per day) in the form of methane again through the breath from which not only the energy balance of these ruminants charged, but also influences the terrestrial greenhouse effect.

The energy balance of entire ecosystems is referred to as energy flow and calculated. Energy balances and energy flows are tightly coupled with the mass balances (see also material and energy exchange ).

History

The theoretical groundwork go to work by L. von Bertalanffy, GG Winberg and other back. S. Brody, M. Kleiber and more focused heavily on studies of domestic animals. First detailed empirical accounts of wild animal species have been developed to freshwater organisms, so to daphnia as balances on individual level from 1958 and on freshwater snails of the genera Ferrissia and Ancylus as balances on individuals and population level from 1971. Starting around 1980, increased molecular aspects of biological energy flows within the bioenergetics investigated.