Energy balance (ecology)

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Energy balance , including energy balance (Engl. Energy budget ), is in the ecology and ecophysiology the name given to the balance-sheet analysis and presentation of continuous energy conversions . It is therefore also a branch of bioenergetics .

Energy balance and energy flow

Energy balances can be measured for a single organism or a population . While in green plants the energy required for metabolism and growth is absorbed in the form of radiation energy , in animals it is obtained as organically bound energy when eating. In both cases, energy is released through growth, offspring production, secretory functions and other processes that require energy.

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

Conceptual approach

Energy balances are defined for certain periods of time, e.g. B. for a second, a day or a year or even over the entire lifetime of the individual. Instead of an energy balance should correct from current account speak ( power = unit of energy per unit time). However, the term “power balance” has not caught on in this context, probably to avoid confusion with the analogous terms used in energy technology and economics.

The energetic units used are those of physical energy (or work ) or power, e.g. B. [J] ( Joule ) or [kJ] for energy balances and z. B. [J / s] (= watt ) or [kJ / d] for power balances (also called rates ).

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

  • C = A + E
  • A = P + R

The following applies here:

In addition, depending on the animal group, there may be other measured variables, such as the energy content released into the environment that is lost through molting (e.g. with insects and snakes ). In many animals, defecation and excretion cannot easily be differentiated by measurement, since the two components are released mixed ( birds , insects).

Measurement methods and sample size

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

Example: A person consumes an energy of 8,000 - 10,000 kJ per day with food, which can, however, fluctuate greatly. In the above formulas this corresponds to the consumption rate C. It enables a metabolic output of 100 W. This value can temporarily increase considerably, e.g. B. to over 200 W with medium-fast walking or when pulling a light car and briefly to over 1000 W with maximum physical exertion. This high amount of energy is expended in the form of the mechanical work performed by the skeletal muscles, the circulatory muscles and the respiratory movements, and also by the cellular expenditure for osmoregulation and molecular transport processes. During all these activities, thermal energy is automatically released, which is a concomitant phenomenon of all energy change processes . The sum of the mechanical, cellular and thermal energy produced is methodically recorded as the respiratory energy R; a breakdown of the individual energy components is often difficult.

Ecological importance

The measurement of energy balances allows fundamental insights into the energy flows in the ecosystem and thus into the understanding of its energy and material balance. Also in the context of behavioral and evolutionary biology, energy balances form an important basis for the formation of theories, since every organism can put its energy intake into either more growth or reproduction or movement activity etc. at the expense of the other energy-requiring activities. Different strategies have developed here in evolution: Predatory mammals and birds consume a relatively large amount of energy for their prey, while crocodiles manage with the principle of lurking with comparatively less energy and can therefore endure longer periods of hunger.

Findings about energy balances and their optimization also form the theoretical basis for calculating production in agriculture , animal husbandry and aquaculture . They also form an important basis for calculating earthly material balances. Cattle release a good 6% of the energy they consume through food (around 300 liters per day) in the form of methane through the air they breathe, which not only affects the energy balance of these ruminants, but also affects the earth's greenhouse effect.

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

history

The theoretical preparatory work goes back to the work of L. von Bertalanffy , GG Winberg and others. S. Brody , M. Kleiber, and others focused heavily on pet studies. The first detailed empirical balances of wild animal species were compiled on freshwater organisms, for example on daphnia as balances at the individual level from 1958 and on freshwater snails of the genera Ferrissia and Ancylus as balances at the individual and population level from 1971. From around 1980 on, molecular aspects of biological energy flows increased within the framework of the Bioenergetics examined.

Individual evidence

  1. ↑ W. Müller, S. Frings: Animal and Human Physiology. 3. A., Springer, Berlin 2007
  2. ↑ Ludwig von Bertalanffy (1957): Quantitative laws in metabolism and growth. Quart. Rev. Biol. 32: 217-231
  3. ↑ Max Kleiber (1961): The fire of life - An introduction to animal energetics. Wiley, New York
  4. ^ S. Richman (1958): The transformation of energy by Daphnia pulex . Ecol. Monogr. 28: 273-291
  5. ↑ Albert J. Burky (1971): Biomass turnover, respiration, and inter-population variation in the stream limpet ferrissia rivularis (SAY). Ecol. Monogr. 41: 235-251
  6. ↑ Bruno Streit (1976): Energy flow in four different field populations of Ancylus fluviatilis (Gastropoda - Basommatophora). Oecologia 22: 261-273
  7. ^ Albert L. Lehninger (1982): Bioenergetics. Molecular basis of biological energy conversions. G. Thieme, Stuttgart