Energy flow and pyramids sim
Turn an efficiency dial for a field chain or an oak tree chain and watch the pyramids of numbers, biomass and energy redraw, see where each level's energy goes, find how many levels the chain can support, and work out transfer efficiency from a data card.
Ecosystems: energy flow along food chains, transfer efficiency and losses, and pyramids of numbers, biomass and energy · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Energy flow and pyramids. A board on the bench shows three pyramids for one food chain, side by side, each with the producers at the bottom: a pyramid of numbers (how many organisms), a pyramid of biomass (their dry mass at one time) and a pyramid of energy (the energy each level gets in a year). The chain stands in front as model organism cards, with arrows from the food to the feeder. Turn the efficiency dial to set the share of each level's energy that ends up in the next level's biomass (1 to 20%): the rest is lost, mostly used in respiration and lost as heat, and also in faeces and urine and in parts not eaten. A level needs a minimum amount of energy to support a population, so the chain can support only so many levels, which is why food chains are short. The oak tree chain shows an inverted pyramid of numbers: one tree feeds thousands of caterpillars, while its pyramid of biomass is still upright. A pyramid of energy is always upright. Real values differ: real transfer efficiencies are often about 10%, and birds and mammals pass on less, because they use so much energy in respiration to keep warm. Simplified on purpose: all the numbers are illustrative (≈), chosen to show the pattern, not measured in a real field or wood; one transfer efficiency is used for every step of the chain; in real chains it differs from step to step; the split of each level's energy is illustrative: 20% lost in faeces and urine and 10% in parts not eaten at every step, with respiration taking the rest, so in this model a higher efficiency comes only out of respiration; the producers store about 1% of the light energy that reaches them (illustrative); each level's energy is rounded to 3 significant figures before the next level is worked out from it, so the shown working adds up; a level needs at least 5 kJ per m² per year to support a population; real limits are not a single number; biomass is the dry mass standing at one time, worked out from each level's yearly energy at about 20 kJ per gram, times how many years of growth that kind of organism holds (an oak tree about 20, a caterpillar about a tenth); numbers are worked out from the biomass and the dry mass of one organism; each chain is treated as if it were alone; in a real habitat each level shares its energy with many other species, so the real numbers of each kind are far smaller, especially for top predators and birds, often by hundreds or thousands of times; the bars are drawn to the stated scale: to scale (linear) or log; a bar too narrow to draw is a dashed stub; the cards and pictures are not to scale.
- Bar width: that level's value, on the scale written under each pyramid
- Dashed stub: a value too small to draw at its true width
- Grey row: a level the chain cannot support (it would get too little energy)
Use it in your lessons
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