Recall Why is only the ENERGY pyramid always upright?
Because energy obeys strict conservation with unavoidable losses (heat, waste) at every transfer, so each level must receive less than the one below. Numbers ignore body size; biomass ignores turnover time. Only energy flow captures the true one-way, ever-shrinking flow.
A feeding position in a food chain (producers = level 1, herbivores = 2, etc.).
What does each layer of an ecological pyramid represent?
One trophic level, drawn to scale for energy, biomass, or numbers.
Unit of an energy pyramid?
kJ m⁻² yr⁻¹ (energy flow per area per time).
Why is the "per year" in the energy unit?
Energy is a flow/rate, not a stored lump; we measure the rate of energy capture.
State the 10% rule.
On average only ~10% of energy at one trophic level is passed to the next.
Where does the other ~90% of energy go?
Respiration (heat), faeces (undigested), and uneaten/dead material to decomposers.
Which pyramid is ALWAYS upright and why?
Energy — conservation plus unavoidable losses means each level gets less than the one below.
Give an inverted numbers pyramid example.
One oak tree → thousands of insect herbivores.
Give an inverted biomass pyramid example.
Ocean phytoplankton (small standing biomass, fast turnover) supporting larger zooplankton.
Biomass vs energy: key difference?
Biomass is a standing-stock snapshot; energy is a rate over time. Biomass can invert; energy cannot.
Formula for energy after k transfers at 10% efficiency?
E_(n+k) = E_n × (0.10)^k.
If producers = 20000 kJ m⁻² yr⁻¹, energy at level 3?
20000 × 0.10² = 200 kJ m⁻² yr⁻¹.
Are decomposers a normal pyramid layer?
No — they draw energy from all levels, so shown separately.
Recall Feynman: explain to a 12-year-old
Imagine a stack of piggy banks, one on top of another. The bottom bank is the plants; they collect sunshine-money. When the next animal up "borrows" money, it spends 9 out of every 10 coins just to run around and stay warm, and only puts 1 coin in its own bank. So each higher bank holds way less money. That's why the stack looks like a triangle — big at the bottom, tiny at the top. And that's why you never see a food chain with 20 levels: the money runs out!
Dekho, ecological pyramid ek bar-chart hota hai jahan har layer ek trophic level dikhati hai — sabse neeche producers (plants), phir herbivores, phir carnivores. Bar ki width batati hai us level pe kitni energy, biomass ya number of organisms hai. Sabse important baat: energy hamesha upar jaate hue kam hoti jaati hai. Kyun? Kyunki jab rabbit grass khaata hai, woh saari energy rabbit nahi banti — 90% toh respiration (heat), faeces aur waste me chali jaati hai. Sirf ~10% hi upar transfer hoti hai. Isko 10% rule kehte hain.
Isliye energy pyramid hamesha upright rehta hai — kabhi ulta nahi ho sakta, kyunki har step pe energy ghatni hi hai (conservation of energy). Formula simple hai: har step pe ×0.10. Agar producers 20000 kJ fix karte hain, toh level 3 pe sirf 20000×0.1×0.1=200 kJ bachti hai. Yahi wajah hai ki food chain 4-5 level se lambi nahi hoti — energy khatam ho jaati hai.
Lekin numbers aur biomass pyramid ulta (inverted) bhi ho sakte hain. Ek bada oak tree (1 producer) hazaaron insects ko feed karta hai — toh numbers pyramid ulta. Samundar me phytoplankton chhote hote hain aur turant kha liye jaate hain, toh unki standing biomass kam hoti hai jabki zooplankton ki zyada — biomass pyramid inverted. Yaad rakho: biomass ek snapshot (stock) hai, energy ek rate (per year) hai. Isliye sirf energy pyramid pe pura bharosa kar sakte ho.
