☰ Contents · Biology

Ecological pyramids and Laboratory work 2

Lessons 19–20 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology Grade 11, 1st edition. Sharq Publishing and Printing Joint-Stock Company, Tashkent, 2018
19

The ecological pyramid rule. Pyramids of biomass and energy

Textbook: pp. 102–105
GoalExplain the ecological pyramid rule, the 10 % rule and the pyramids of numbers, biomass and energy; calculate mass and energy along a food chain.
New words
ecological pyramid · ekologik piramida10 % rule (Lindeman) · 10 % qoidasi (Lindeman)pyramid of energy · energiya piramidasibiomagnification · biologik to‘planish
Explanation

When passing from one trophic level to the next, most of the eaten food is spent on respiration (heat), movement, reproduction and undigested waste, so only about 10 % of the energy (Lindeman’s rule; 5–20 % in practice) reaches the body of the next level. Hence numbers, biomass and energy decrease upward along a food chain – the ecological pyramid rule found by C. Elton (1927); a chain usually has 4–5 links and never more than six. There are three kinds of pyramid: numbers (individuals per level; can be inverted in a tree–insect chain), biomass (dry mass; in aquatic ecosystems phytoplankton biomass can be lower than zooplankton biomass, giving an inverted pyramid, because it renews so fast) and energy (energy flow per unit time; never inverted). In calculations, going up a level means dividing by 10 and going down means multiplying by 10: 1 kg of a top predator needs about 1000 kg of plants (three steps). Persistent poisons (DDT, heavy metals) accumulate in fat and increase up the chain (biomagnification), so the top predator is poisoned most.

Worked examples
Energy chain: grass 40 000 kJ → grasshopper 4000 kJ → lizard 400 kJ → steppe eagle 40 kJ. Each step is divided by 10. For each 1 kJ in the eagle, 1000 kJ is needed in the grass.
For one cormorant of 1 kg dry mass to feed (phytoplankton → daphnia → small fish → cormorant), 1 · 10 · 10 · 10 = 1000 kg dry mass of phytoplankton must be produced. Thanks to rapid renewal this much can form in a year, even though the standing stock in the lake at one time is smaller.
Class activity

Class «energy staircase» model: 10 students act out a chain – the first holds 100 paper balls, and at each handover only 10 % is passed on. Find after how many links no balls remain and write the conclusion. Do not run or throw the balls during the game.

Practice
1
State the 10 % rule in your own words.
2
Chain: grass → mouse → snake → eagle. If grass holds 80 000 kJ, how many kJ reach the eagle?
3
An eagle has a mass of 3 kg (chain grass → mouse → snake → eagle). How many kg of grass are needed?
4
Why may a biomass pyramid be inverted in an aquatic ecosystem but an energy pyramid never?