Life History: aspects of the natural history of an organism that are related directly to survival and
Life history traits include:
- Age of first reproduction (maturity)
- Number of reproductive events (parity)
- Number and size of offspring (fecundity)
o As many offspring as you can for reproductive success
- Longevity (life span)
o Important especially when reproducing multiple times
Should I breed or should I grow?
- Where is the energy going?
If you put energy towards maintenance, there won’t be energy for
There will be trade offs
- Energy allocation: totally energy = maintenance + storage + growth + reproduction
- Trade-offs: resources used for one function cannot be used for another function
Growth and Reproduction
- Larger the ring, the more it grew that year (relative width)
- Negative correlation
- Energy into either growth or reproduction, larger trees produced less cones
The Perfect Organism
- Mature at birth
- Be able to reproduce constantly and produce lots of high quality offspring - Live forever
o These pictures are not actual perfect organisms. They do have certain
o Egg of Kiwi bird takes up 20% of female’s body weight. Yolk is 60% of the egg.
The yolk sac is attached to the offspring so it can feed from it for up to 10 days
o The offspring will be mature at birth and be of higher quality.
Energy budget will clearly change over time.
- As individual ages it will reach different milestones
- Baby possum is highly dependent on mother and most energy will come from the mother
- The baby becomes independent at juvenile stage. The energy is going to the same
place but it has to get its own food supply.
- Once it reaches maturity some energy is going towards reproduction
- Where energy goes and comes from will change between species over their entire life
Fecundity and Adult Survival
- Two trends are opposite
- Optimal parental investment where two lines cross
o Parent maximizing their energy and still taking care of young
- Looking at lifetime reproductive success (P+F)
- If present investment is lower, then will have higher present reproductive success
Why do individuals age and die?
- Many organisms goes under senescence (decreased fertility and decreased probability
of survival). Chance of surviving the next year is less every year.
- Aging should be opposed by natural selection. Why hasn’t this occurred?
- Theories on why aging occurs:
o Rate-of-living theory: populations lack genetic variation to respond to aging
o Evolutionary theory: trade-off between reproduction and repair
- individuals selected to its maximally resist cell damage and repair cell/tissue
- higher metabolic rates age faster, die sooner - no way to increase life span through further selection if we have hit its maximum
o true, we predict that:
because cell/tissue damage byproduct of metabolism, rate of aging
corresponds to metabolic rate
because selected for maximum cell repair, can’t increase longevity
through further selection
- Prediction #1: all species have same amount of energy throughout their life
o Some ‘spend’ it slowly and others quickly
predict that high metabolic rates should have shorter life spans they are
spending their energy much more quickly
see that lifetime energy varies b/w different groups
• bats have similar metabolic rate similar to other rodents but live
• marsupials don’t have a lot of lifetime energy; it is opposite of what
we would predict
Do species with higher metabolic rates have shorter life spans? NO
- Prediction #2: can’t select for longer life span as already at maximum
2 groups selected for early reproduction, 2 groups selected for late
Longevity in late reproducing selected lineages significantly higher
Early reproducing, nothing changed, li