2011-17_Life - EVOLUTION (11:704-486) LIFE HISTORY...

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EVOLUTION (11:704-486) LIFE HISTORY EVOLUTION S MOUSE – SPRING 2011 1 Life History Evolution Life History Tradeoffs: We’ve talked just a bit about the tradeoffs between survival and reproduction. In salmon, it pays to wait, in terms of the number of progeny one can produce, but the survival curve is steep enough (that is to say, survival rate is low enough) that sometimes it is not worth the cost of waiting long enough to put out a lot of eggs. The Issue – The real issue is how the organism is to allocate its reproductive effort. Is it better to produce a few progeny, rapidly, or to produce a lot, but later? Is it better to produce large, well developed offspring, or many small, immature offspring? Is it better to produce progeny all at once, and then die, or better to produce progeny, just a few at a time? These strategies are all under natural selection, and different critters do it differently, depending on the pressures. Size vs Numbers of Offspring – Many bivalves, other marine invertebrates and fishes produce thousands or millions of tiny eggs, as do elm trees. Coconut palm produces a few dozen, each weighing several kilos; a blue whale gives birth to a single offspring weighing more than a full-grown elephant; a kiwi has one egg that weighs  of its body weight. Age at Reproduction – I've already pointed out that bacteria can reproduce in a few minutes to an hour, but some animals and plants take decades to reach reproductive maturity. Some organisms have a brief life, measured in days; others live for centuries. Why is that so? Life Tables – For any given organism, we can describe survival probability and reproductive output as a function of age. One major distinction we need to recognize is whether the organism is iteroparous (several bouts of reproduction) or semelparous (all at once). An annual plant is semelparous; it reproduces in late summer or early fall, and then dies. A pine or an oak is iteroparous; it lives and reproduces for many years. An individual's reproductive contribution is integrated over its entire lifetime Age (x) Survival Probability l x Fecundity m l x m x
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EVOLUTION (11:704-486) LIFE HISTORY EVOLUTION S MOUSE – SPRING 2011 2 dx m l Death Birth on Contributi ve Reproducti Total x x . An individual that produces 3 offspring by age 2 will outcompete one that produces 3 offspring by age 3. Everything else being equal, it pays to get there early. We usually take the view that an offspring now is worth more than an offspring later, that ‘a bird in hand is worth two in the bush’, everything else being equal. We discount future reproductive investments with a compound interest rate, by solving for r in the equation dx m l e - rx Death Birth 1 x x . We then take that rate,
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This note was uploaded on 08/18/2011 for the course ECOLOGY 301 taught by Professor Staff during the Spring '11 term at Rutgers.

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2011-17_Life - EVOLUTION (11:704-486) LIFE HISTORY...

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