WHY the log scale? Because a constant proportion dying per unit time (say 50% each year) shows up as a straight line on a log axis. This lets us instantly read the death rate from the slope — steep slope = high mortality, flat slope = low mortality. On a linear axis these patterns look like confusing curves; log makes them interpretable.
Number/proportion of surviving cohort members (log scale) vs age.
Why use a log y-axis for survivorship?
A constant proportional death rate becomes a straight line, so slope = mortality rate.
Type I curve shape and example?
Flat then steep plunge; low juvenile mortality, deaths late — humans, elephants.
Type II curve shape and example?
Straight diagonal (log axis); constant death rate at all ages — many birds, hydra.
Type III curve shape and example?
Steep early drop then level; high juvenile mortality — oysters, fish, trees.
Formula for survivorship lx?
lx=Nx/N0 (survivors at age x ÷ starting cohort).
What does the slope of a survivorship curve represent?
The mortality (death) rate at that age.
Which type is r-selected vs K-selected?
Type III ≈ r-selected (many cheap offspring); Type I ≈ K-selected (few, cared-for offspring).
On a log axis, does a straight line mean constant number or constant proportion of deaths?
Constant proportion (percentage), not constant number.
Recall Feynman: explain to a 12-year-old
Imagine 1000 baby turtles hatch on a beach. If most get eaten by birds in the first hour but a few reach the sea and live 80 years — that's Type III (baby danger). Now imagine 1000 human babies: almost all live to be old, then die around the same old age — that's Type I (old-age deaths). And some birds are just as likely to die young or old — that's Type II (steady risk). Draw how many are still alive as they age, and the shape of the line tells you which turtle-or-human story you're looking at.
Survivorship curve ka matlab simple hai: 1000 newborn lo, aur dekho har age pe kitne abhi bhi zinda hain. Us count ko (log scale pe) age ke against plot kar do — line ka shape hi batata hai ki species kaise jeeti aur marti hai. Log scale isliye use karte hain kyun ki agar har saal ek fixed percentage mar raha ho, toh log pe woh ek seedhi line ban jaati hai, aur slope se mortality rate turant padh sakte ho.
Teen classic types yaad rakho. Type I (jaise insaan, hathi): shuru mein bahut kam maut, line flat rehti hai, phir budhape mein tez girti hai. Type III (jaise oyster, machhli, ped): shuru mein hi bahut saare baccho ki maut, line ekdum se girti hai phir flat ho jaati hai — kyunki jo bach gaye woh lambi umar jeete hain. Type II (jaise kai birds): har age pe barabar death rate, isliye log pe ek seedhi diagonal line.
Iske peeche strategy hai — quantity vs quality ka trade-off. Type I / K-selected species thode hi bacche paida karte hain par unki poori care karte hain (isliye bacche survive karte hain). Type III / r-selected species hazaaron bacche paida karte hain bina care ke — zyada tar mar jaate hain, par kuch winners bach jaate hain. Yeh strategy weak nahi hai, yeh ek numbers game hai!
Sabse badi galti students karte hain: seedhi line ko samajhte hain "har saal same number marte hain". Nahi! Log axis pe seedhi line ka matlab same proportion (percentage) marte hain — 1000 → 500 → 250, number kam hota jaata hai par rate constant. Aur hamesha y-axis check karo linear hai ya log, warna type galat pehchan loge.
