12 julio, 2024

What is the Ecological Tithe Law? fundamental concepts

What is the ecological tithe law?

The ecological tithe law, ecological law either 10%states that an organism can capture only 10% of a higher trophic level (the trophic level is the level at which a set of organisms in an ecosystem coincide in the food chain).

Energy moves from one trophic level to the next, and in the process much of the energy is lost in respiration. This occurs because of the Second Law of Thermodynamics, which says that: «all mechanical work can be converted into heat, but not all heat is converted into mechanical work.»

This is the basis of ecological energy, which establishes that plants take advantage of 90% of solar energy, herbivores (primary consumers), when eating them, access the remaining 10%, of which they will use 90% for their metabolic processes, and carnivores (secondary consumers), when eating herbivores, will in turn use 10%.

In other words, of the 100% of energy that an organism Y captures, 90% is used for vital processes, such as maintaining metabolism, movement, growth, etc. Another organism, T, feeding on it, will only get 10% of Y’s initial energy, and so on, all the way to the top of the food pyramid.

fundamental concepts

Gross and net primary productivity

Primary productivity is the rate at which biomass is produced per unit area.

It is usually expressed in energy units (joules per square meter per day), or in dry organic matter units (kilograms per hectare per year), or as carbon (carbon mass in kg per square meter per year).

In general, when we refer to all the energy fixed by photosynthesis, we usually call it gross primary productivity (PPG).

Of this, a proportion is spent on respiration by the autotrophs (RA) themselves and is lost in the form of heat. The net primary production (PPN) is obtained by subtracting this quantity from the PPG (PPN= PPG-RA).

This net primary production (PPN) is what is ultimately available for consumption by heterotrophs (bacteria, fungi, and other known animals).

secondary productivity

Secondary productivity (PS) is defined as the rate of production of new biomass by heterotrophic organisms.

Unlike plants, heterotrophic bacteria, fungi, and animals cannot make the complex, energy-rich compounds they need from simple molecules.

They obtain their matter and energy always from plants, which they do directly by consuming plant material, or indirectly by feeding on other heterotrophs.

In this way, plants or photosynthetic organisms in general (also called producers), make up the first trophic level in a community; primary consumers (which feed on producers) make up the second trophic level, and secondary consumers (called carnivores) make up the third trophic level.

Transfer efficiencies and energy pathways

Energy transfer efficiency categories

There are three categories of energy transfer efficiency with which the pattern of energy flow at trophic levels can be predicted.

These categories are: consumption efficiency (EC), assimilation efficiency (EA) and production efficiency (EP).

– Mathematically, we can define the consumption efficiency (EC) as follows:

CE=In/pn-1 ×100

The EC is a percentage of the total productivity available (pn-1), which is actually ingested by the next higher trophic compartment (In).

For example, for primary consumers in the grazing system, EC is the percentage (expressed in units of energy and per unit of time) of NPP consumed by herbivores.

If we were referring to secondary consumers, then it would be equivalent to the percentage of herbivore productivity consumed by carnivores. The rest die without being eaten and enter the decomposition chain.

– The assimilation efficiency (EA) is expressed as follows:

EA=still/In ×100

It is also a percentage, but this time it is the part of the energy coming from the food, and ingested in a trophic compartment by a consumer (In), assimilated by your digestive system (still).

Said energy will be that available for growth and for the execution of work. The remainder (the unassimilated part) is lost in the feces and enters the trophic level of decomposers.

– Production efficiency (PE) is expressed as:

PE=Pn/W × 100

It is also a percentage, but in this case we refer to the assimilated energy (still) that ends up being incorporated into new biomass (PN). All the unassimilated energy remnant is lost as heat during respiration.

Products such as secretions and/or excretions (rich in energy), which have participated in metabolic processes, can be considered as production, PNand are available, as corpses, to decomposers.

Overall transfer efficiency

The «global transfer efficiency» from one trophic level to the next is given by the product of the aforementioned efficiencies (EC x EA x EP).

Expressed colloquially, the efficiency of a level is given by what can be effectively ingested, which is then assimilated and ends up being incorporated into new biomass.

Where does the lost energy go?

To answer this question we must draw attention to the following facts:

– Not all plant biomass is consumed by herbivores, as much of it dies and enters the trophic level of decomposers (bacteria, fungi and other detritivores).

– Not all the biomass consumed by herbivores, nor that of herbivores consumed in turn by carnivores, is assimilated and available to be incorporated into the biomass of the consumer; a part is lost with the feces and passes to the decomposers.

– Not all the energy that is assimilated is actually converted into biomass, since a part is lost as heat during respiration.

This happens for two basic reasons: firstly, due to the fact that there is no 100% efficient energy conversion process.

That is, there is always a loss of heat in the conversion, which is in accordance with the Second Law of Thermodynamics.

Secondly, because the animals need to do work, which requires energy expenditure and, in turn, implies new losses in the form of heat.

These patterns occur at all trophic levels, and as the Second Law of Thermodynamics predicts, part of the energy that is attempted to be transferred from one level to another is always dissipated as unusable heat.


Caswell, H. Food Webs: From Connectivity to Energetics. Advances in Ecological Research.
Curtis, H. et al. Biology. 7th Edition. Buenos Aires-Argentina: Panamerican Medical Editorial.
Lindemann, RL The trophic–dynamic aspect of ecology.

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