PSYCH
Lecture 3 - life history theory overview 2017.pdf

They invest a lot of resources in keeping their

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They invest a lot of resources in keeping their bodies repaired, slowing the pace of aging and extending lifespan. The elephant exemplifies a “slow” life history species
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How do species with these different life history strategies evolve?
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2 principles that shape life histories: I. Organisms have finite energy and time to invest in different functions, leading unavoidably to trade-offs: Current vs. future reproduction Offspring size/quality vs. number of offspring Size at maturity vs. age at maturity II. Extrinsic (unavoidable) mortality: helps determine whether a species can afford to be “slow” or whether they must be “fast”
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Finite energy leads to trade-offs
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FOOD / ECOLOGY Maintenance Growth Activity Energy Reserve (fat) Adult Reproduction Activity Maintenance Reserve (fat) Pre-adult “productivity” Energy allocation within the body
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Organisms have finite time and energy Trade-offs are thus unavoidable Growth ( Æ Reproduction) • Maintenance Physical activity Extra: Storage (fat) 200 600 200 1,000 Growth Maintenance Activity Storage The “Allocation Rule” Example: 2,000 Kcal / day
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Why do our bodies have “finite energy”, and what determines the size of our energy pie?
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Scaling of energy metabolism BMR ~ Mass 0.75 After Hemmingsen 1960
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Photo: GB West (with permission)
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Figure: GB West (with permission) One recent proposal: ¾ power scaling emerges from fractal distribution networks, which optimize efficiency West et al (1997), Science, 276(5309):122-6. West et al (1999), Science, 284(5420): 1677-9. West et al (2002) PNAS, 99 (Suppl 1) 2473-8
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Scaling of plant growth rate Niklas KJ & Enquist BJ (2001) PNAS, 98 (5) 2113-4
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Scaling of plant growth rate Niklas KJ & Enquist BJ (2001) PNAS, 98 (5) 2113-4
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Metabolic scaling implies constraints on available energy The capacity to distribute resources is finite and linked with a species’ mass. Human
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Natural selection has been constrained by physics in the total energy available to a given species (size of the pie), which is linked with their body size. This leads unavoidably to trade-offs. Again, a few key ones include: 1. Current vs. future reproduction 2. Quality vs. number of offspring 3. Size vs. age at maturity Energy partitioning
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Life history trade-off #1: Current vs. future reproduction Reproducing now comes at a cost to reproducing in the future. This can occur through two pathways: By reducing resources available for future offspring e.g. depletion of body fat or micronutrient stores By reducing maternal survival into the future examples: mortality in child birth; sapping nutritional reserves Æ reduced immune function; reduced tissue repair Æ more rapid aging
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The trade-off between current and future offspring is often referred to as the “cost of reproduction”
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Life history trade off #2: Number vs. quality of offspring
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y = 2.27x -0.15 R 2 = 0.15 10 100 1 Litter size Newborn size Primates: Trade-off between # vs. quality (litter size vs. newborn size)
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Litter size Survival # offspring surviving 1 95% 0.95 2 75% 1.50 3 55% 1.65 4 35% 1.40 5 15% 0.75 Example: predicting “optimal” strategy What would we need to know to estimate how large of a litter an organism will be predicted to have if it is maximizing its fitness?
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  • Winter '08
  • McCaslin
  • Evolution, IBI, Life history theory

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