11: Life-History strategies: trade-offs in survival and reproduction

Life history

timing and pattern of survival, growth, and reproduction

suite of traits related to a species’ lifespan and the timing and pattern of reproduction

(size at birth, growth pattern, age and size at maturity, numbersizeandsexratio of offspring, etc)

Survivorship curve

plot of the proportion of numbers in a cohort still alive at each age and shows the pattern of survivorship for a population

may be plotted on a LOG SCALE

if on log scale, a straight curve means constant rate of death

Why don’t organisms live for a long time and reproduce a lot?

allocation and tradeoffs

Allocation

Resources have to be invested on the triangle of growth vs survival vs reproduction

Limited resources need to be allocated to only some parts of the triangle

Tradeoff

Occurs when investing in one corner of the triangle had benefits and consequences compared to investing in a different corner

What can tradeoff graphs tell you

It can tell you the pattern of a tradeoff, but canNOT tell you the mechanism

Tradeoff between size and amount of offspring

Species can either have moresmaller or fewerbigger offpsring

How is reproduction allocated?

Increased current reproduction can decrease future reproduction and vice versa

Can environments change allocation?

Yes, environmental stress can lead to abandoning kids in food shortage to prioritize future offspring survival

When less food, adult has higher value of survival

BUT, if we talking about a short-life semelparous (reproduce once then dies) organism, they might sacrifice themselves instead