Ecological Efficiency

Ecological efficiency refers to the efficiency with which energy and matter are transferred between trophic levels in an ecosystem. It is a measure of how much of the energy or biomass acquired by an organism is actually incorporated, rather than being dissipated and lost from the system.

Types of Ecological Efficiencies

There are different types of ecological efficiencies analyzing various ecosystem transfers.

Assimilation Efficiency

Assimilation Efficiency refers to the percentage of the food consumed (prey) that is actually digested and assimilated into the body of the consumer (predator). The rest passes out as faeces.

• For example, a cow may consume 100 kg of grass but can only digest 40 kg effectively assimilating it into its body tissues. So the assimilation efficiency is 40%.
• In terms of energy, if a gazelle takes in 1000 kcal through eating plants but assimilates only 500 kcal into its bodily tissues, its assimilation efficiency is 50%.

Higher animals tend to have assimilation efficiencies ranging from 50-90%. Detritivores and decomposers however utilize already broken down organic matter and thus have very high assimilation efficiencies of 90% or greater.

Production Efficiency

Production Efficiency measures how much new biomass an organism can produce relative to the amount of biomass it has consumed and assimilated.

• For example, after digesting and assimilating 40 kg of grass, if the cow in the earlier example is able to convert 18 kg into its own body weight as new growth, its production efficiency is 45% (18 kg produced/40 kg assimilated).
• In terms of energy, if from the above 500 kcal, the gazelle converts 200 kcal into muscle and organ tissue growth, its production efficiency is 40%.

Plants tend to have production efficiencies of 42 – 47%.

Ecological Efficiency

Ecological Efficiency refers to the efficiency of transfer of biomass from one trophic level (organisms that share the same position in a food chain) to the next. It accounts for all the losses during eating, digesting, assimilating and converting food into new tissue at every trophic level exchange.

Typically only about 10% of the energy is successfully transferred between each trophic level.

• For example, say 100 kg of grass is consumed by a herbivore. Only 50 kg was actually assimilated after digestion by the herbivore. Of this, only 20 kg was converted into the herbivore’s own new body tissues. If this herbivore is then eaten by a carnivore, about 10% (or 2kg) of this biomass will probably be transferred to and assimilated by the carnivore.
• Taking ahead energy example, if the gazelle above offers 2000 kcal to a lion through eating, the lion will likely assimilate only 200 kcal – a transfer efficiency of 10%.

Net Production Efficiency

This refers to the efficiency with which plants in an ecosystem convert the sunlight they receive into biomass or primary production through photosynthesis. Different ecosystems vary in net primary production based on climate, plant densities and species, limiting factors like water etc. Tropical rainforests often have very high net production efficiencies of 30 – 35% compared to other ecosystems.