Energy transfer through ecosystems

Energy transfer and its efficiency
Nutrient recycling by microorganisms

Energy transfer and its efficiency

As seen previously, plants produce a great deal of energy which is used up increasingly at every trophic level. This is the basis on which decisions are made in agriculture and rearing of domestic livestock.

In the wild, both plants and animals are subject to a lot of energy loss due to pests, physical activity or insufficient nutrients. This results in a relatively inefficient flow of energy between trophic levels. We think of this in terms of net productivity.

Net productivity is equal to gross productivity minus respiratory loss.

In both terms, productivity refers to the amount of leftover useful tissue such as cereals or animal flesh.

Gross primary production (GPP) is the chemical energy stored in plant biomass in a specific area or volume, while net primary production (NPP) is the chemical energy store in plant biomass after accounting for respiratory losses (R) to the environment.

This gives NPP = GPP – R

NPP can end up in plants’ own growth and reproduction or it can be taken up by herbivores and decomposers.

Consumers such as animals have their own net production termed N which becomes equal to:

N = I – F + R, where

I = chemical energy stored in Ingested food
F = chemical energy lost to the environment in Faeces and urine (stay classy)
R = chemical energy lost in respiration

The rates of productivity for primary and secondary production respectively are primary and secondary productivity. These can be expressed as energy per area per time, e.g. kJ ha-1 year-1, which is kilojoules per hectare per year.

As opposed to the wild, in human-made growth environments this respiratory loss is kept as low as possible. Extreme measures are taken to achieve this, which include:

1. The use of chemical pesticides and biological agents to kill all or certain organisms which may infect or feed on plants e.g. insects, fungi, small animals

2. Intensive rearing of animals which includes keeping them indoors and in confined spaces to prevent their energy being lost on movement; and administering antibiotics to prevent mass spread of infection

To enhance plant growth fertilisers are used, whether natural (manure) or …

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