Ecology

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Efficiency of Biomass Transfers

The efficiency of biomass transfer affects the number of organisms that can be maintained in different trophic levels. The efficiency of biomass can be expressed using percentages and fractions.

$Thistle \rightarrow goldfinch \rightarrow sparrow \space hawk$ What is the average percentage of biomass that is passed on from the producer to the primary consumer in this food chain?

So on average, only $10\%$ of biomass in a trophic level is passed on to the next trophic level. This can vary, though, depending on the organisms involved and the abiotic conditions in the ecosystem. Which of these could lead to a higher than average loss of biomass?

You can select multiple answers

$Thistle \space 1250g \rightarrow goldfinch \space 138.75g \rightarrow sparrow \space hawk \space 13.46g$

How much of the biomass from thistles is passed on to the biomass of finches? Give your answer in percent.

Which one of these options shows how you worked out the percentage of biomass passed on from thistles to goldfinches?

Which one of these options is the correct generalised formula then for working out the % efficiency of biomass transfer from one trophic level to the next?

$\% \space efficiency \space of \space transfer = \frac{biomass \space of \space higher \space trophic \space level}{biomass \space of \space lower \space trophic \space level} \times 100\%$

Remember, the lower trophic level goes in the lower part of the fraction (the denominator).

So we can calculate the efficiency of biomass transfer by comparing the dry biomass **** of two trophic levels in a fraction: $\frac{biomass \space of \space higher \space trophic \space level}{biomass \space of \space lower \space trophic \space level}$ .

We can change this to a percentage by multiplying by 100: $\frac{biomass \space of \space higher \space trophic \space level}{biomass \space of \space lower \space trophic \space level} \times 100\%$

$Thistle \space 1250g \rightarrow goldfinch \space 138.75g \rightarrow sparrow \space hawk \space 13.46g$ What is the percentage efficiency of the biomass transfer between the goldfinches and the sparrow hawks?

$Thistles \rightarrow goldfinch \rightarrow sparrow \space hawk$ What fraction of the biomass from the thistles has been passed on to the sparrow hawks?

What happens to the overall amount of food (biomass) available to each trophic level as you move along the food chain?

So the amount of biomass (food) decreases at each new level. What happens to the population size of each level as you move along the food chain?

$Thistle \rightarrow goldfinch \rightarrow sparrow \space hawk$ In a predatory food chain, such as this one, we will find a decrease in population size as we move up the trophic levels because less and less food will be available. There might be hundreds of thistles, a flock of 30 goldfinches and maybe just 1 or 2 sparrow hawks.

$Oak \space tree \rightarrow aphids \rightarrow ladybirds \rightarrow blue \space tits$ The first part of this food chain is parasitic. **** The aphids don't kill and eat the tree, they live off it, whilst the tree is still alive. Here, there is one tree, thousands of aphids, hundreds of lady birds and 2 or 3 blue tits. What happens to the biomass as it we move from the Oak towards the aphids?