BIOL1003 Lecture Notes - Lecture 7: Semelparity And Iteroparity, Ecological Succession, Primary Succession
BIOL1003: Module 4 – Ecology
Lecture 7 – Optimising Reproduction
1. When resources are limited, an increase in reproductive effort (and output) leads to somatic
costs (a reduction in investment in growth)
2. These somatic costs reduce future fecundity (the probability of surviving to breed again)
3. There is a trade-off between current reproduction and residual reproductive value.
4. This trade-off is optimised by natural selection
• Larger organisms tend to be slower to reach reproductive age (E. coli - about 20mins, humans
or elephants - about 10-14 years
• Current reproduction may be favoured when there is no carrying capacity pressure, no
competition - ecological succession
• Ecological succession
o Primary succession occurs where no soil exists when succession begins
• Small habitus plants fix nitrogen then make soil
• More complex plants can the grow
• Hundreds of years, it might become a more complex forests
o Secondary succession begins in an area where soil remains after disturbance
• When growing big gets risky
o Indeterminant growth - keep growing as with food availability
o Reproduce when younger because big size makes them vulnerable to predation
o Salon return to their natal rivers to spawn (salt-fresh water)
• Once they are in fresh water, there is no going back to the ocean
o Eels - live in fresh water but go out to sea to spawn
• No turning back again
o Called life history strategies
• Iteroparity versus semelparity
o Iteroparity: have multiple breeding season, reproduce time and time again
o Semelparity: there is only 1 breeding season (they can only reproduce once)
• Human societies change predictably from high birth and death rates to low birth and death
rates
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