Biology 3300- Life Histories & Trade-Offs

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University of Lethbridge
BIOL 3300
Theresa Burg

Biology 3300 th Mar.12 Life History: aspects of the natural history of an organism that are related directly to survival and reproduction 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? o Maintenance o Reproduction o Storage o Growth  If you put energy towards maintenance, there won’t be energy for reproduction  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 characteristics though. 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 after birth. 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 Rate-of-Living Theory - 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 longer • 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 reproduction  Longevity in late reproducing selected lineages significantly higher  Early reproducing, nothing changed, li
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