5.2.6
Ek survivorship curve bas yeh picture hai ki death kab hoti hai ek lifespan mein. Socho ki tum 1000 newborns ko birth se death tak follow kar rahe ho aur pooch rahe ho: "Har age par kitne abhi bhi zinda hain?" Woh plot karo, aur line ki shape tumhe ek species ki poori life-and-death strategy bata deti hai — chahe woh kuch bachon ki fiercely raksha kare, ya duniya mein offspring flood kare aur zyaadatar ko maarne de.
Ek survivorship curve ek cohort ke surviving individuals ki sankhya (ya proportion) ko age ke against plot karti hai, usually logarithmic (log) y-axis par, 1000 individuals ke ek standard cohort se shuru hokar.
Cohort ::: un individuals ka group jo sab ek hi samay par paida hue hain , saath track kiye jaate hain.Y-axis hai log 10 ( survivors )
WHY the log scale? Kyunki ek constant proportion jo har unit time mein marti hai (maan lo 50% har saal) log axis par ek straight line ke roop mein dikhti hai. Isse hum turant slope se death rate padh sakte hain — steep slope = high mortality, flat slope = low mortality. Linear axis par yeh patterns confusing curves jaisi lagti hain; log unhe interpretable banata hai.
Definition The Three Types
Type I ::: low juvenile mortality, zyaadatar deaths late in life. Curve flat hoti hai phir plunge karti hai . (Humans, elephants, whales.)Type II ::: sabhi ages par constant death rate. Curve ek straight diagonal line hai (log axis par). (Bahut se birds, hydra, kuch rodents/lizards.)Type III ::: high juvenile mortality, early mein bahut kam survive karte hain, survivors zyada jeete hain. Curve steeply drop hoti hai phir level ho jaati hai . (Oysters, fish, insects, bahut se plants/trees.)
HOW slope story batata hai: Kisi bhi point par slope = uss age par mortality rate.
Type I: early mein shallow slope (kam young maarte hain), late mein steep slope.
Type II: har jagah same slope (death rate age se independent).
Type III: early mein bahut steep slope (young ka massacre), late mein shallow.
Worked example Example 1 — Identify the typeEk life table dikhata hai: 1000 acorns mein se, 90% year 1 mein germinate-fail ya kha liye jaate hain, 100 bachte hain; un 100 seedlings mein se, ~90 har agle saal decades tak survive karte hain.
Which type?
Step: Bahut bada early loss (1000 → 100). Why this step? Steep early drop = high juvenile mortality — Type III ki pehchaan.Step: Survivors phir decades tak persist karte hain (shallow late slope). Type III ki "level tail" se consistent.
Answer: Type III.
Worked example Example 2 — Compute survivorshipCohort N 0 = 1000 N 5 = 850 N 60 = 500 N 80 = 50
l 5 = 850/1000 = 0.85 Why? Directly l x = N x / N 0 l 60 = 500/1000 = 0.50 l 80 = 50/1000 = 0.05 Interpret: Survivorship high rehti hai (0.85, 0.50) phir collapse karti hai (0.05). Flat-then-plunge = Type I (jaise humans).
Why this step? Yeh compare karna ki bada drop kahan hota hai (late mein) type fix karta hai.
Worked example Example 3 — Read a slopeEk log plot par, Type II mortality 50% per year hai. 1000 se shuru karke: year1 = 500, year2 = 250, year3 = 125.
Har step 0.5 se multiply karta hai → N x = 1000 × 0. 5 x
log N x = log 1000 + x log 0.5 constant slope log 0.5 ≈ − 0.30 Why this step? Ek constant proportion ka marna log axes par constant slope deta hai = Type II ke liye defining test.
Common mistake "Straight line ka matlab deaths ki constantnumber hai."
Why it feels right: Ek straight line ek steady, even decline jaisi lagti hai.
The fix: Ek log axis par straight line ka matlab ek constant proportion (percentage) hai, constant number NAHI. Agar 50% har saal maarte hain, toh woh 500 phir 250 phir 125 hai — deaths ki sankhya shrink hoti hai chahe rate constant ho.
Common mistake "Type III animals weak / poorly adapted hain kyunki itne maarte hain."Why it feels right: Massive infant death failure jaisa lagta hai.
The fix: High early death ek successful strategy hai — lakhos saste offspring produce karna taaki ek tiny survival % bhi population maintain kare. Yeh ek numbers game hai, koi defect nahi.
Common mistake Linear-axis curve ko aise padhna jaise woh log ho.Why it feels right: Ek curve ek curve hoti hai.
The fix: Hamesha y-axis check karo. Type II sirf log scale par straight line hoti hai; linear scale par woh curve karti hai. Axis ko galat samajhna tumhari classification ulat deta hai.
What does a survivorship curve plot? Cohort members ke surviving number/proportion (log scale) vs age.
Why use a log y-axis for survivorship? Ek constant proportional death rate straight line ban jaati hai, toh slope = mortality rate.
Type I curve shape and example? Flat phir steep plunge; low juvenile mortality, deaths late mein — humans, elephants.
Type II curve shape and example? Straight diagonal (log axis); sabhi ages par constant death rate — bahut se birds, hydra.
Type III curve shape and example? Steep early drop phir level; high juvenile mortality — oysters, fish, trees.
Formula for survivorship l x l x = N x / N 0
What does the slope of a survivorship curve represent? Uss age par mortality (death) rate.
Which type is r-selected vs K-selected? Type III ≈ r-selected (bahut se saste offspring); Type I ≈ K-selected (kum, cared-for offspring).
On a log axis, does a straight line mean constant number or constant proportion of deaths? Constant proportion (percentage), constant number nahi.
Recall Feynman: explain to a 12-year-oldSocho 1000 baby turtles ek beach par hatch hote hain. Agar zyaadatar pehle ghante mein birds kha jaate hain lekin kuch samundar tak pahunch kar 80 saal jeete hain — woh Type III hai (baby danger). Ab socho 1000 human babies: almost sab budhape tak jeete hain, phir usi budhape ke aaspaas maarte hain — woh Type I hai (old-age deaths). Aur kuch birds young ya old hone par utni hi likely maarte hain — woh Type II hai (steady risk). Draw karo ki age badhne par kitne abhi bhi zinda hain, aur line ki shape tumhe bata deti hai ki tumhara kaun sa turtle-ya-human wala story chal raha hai.
"1 = Live long, 3 = Die young, 2 = In-between (steady stream)."
Yeh bhi: Type I ek cliff ke top jaisa lagta hai (flat phir edge se drop = budhape mein maro); Type III ek ski jump jaisa lagta hai (jaldi drop hota hai phir flat ho jaata hai = young mein maro).
Life Tables and Cohort Analysis — in curves ko banane ke liye data source.r-selection and K-selection — Types III aur I ke peeche evolutionary strategies.Age Structure and Population Pyramids — related demographic snapshots.Exponential and Logistic Growth — mortality patterns growth models mein feed hote hain.Reproductive Strategies (Semelparity vs Iteroparity) — offspring investment curve type se link karta hai.
Cohort of 1000 born together
Type II straight diagonal
Type III steep then levels
K-selected few offspring, high care
r-selected many offspring, no care
