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Lecture 19 - BIO220

diff colours are diff projections of how the

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Unformatted text preview: fertilizers, biocides -Birth rates have been high for most of human history -DEATH RATES ARE CHANGING - they are lowering ! -Diff colours are diff projections of how the populations can g row -Our rate of growth has slowed since the 70's (1.2% from 2%) -We either need more birth or less dying to level it off! 2 20/03/2013 Age structure affects trajectory • Fast growing populations have broad based age pyramids, excess of children, population momentum • Even if r goes to zero, populations keep growing as children reach reproductive age High momentum Low momentum Is recent human trajectory an unsustainable overshoot or evidence of elastic parameters? • Calculating carrying capacity is HARD! Age pyramids from Scotland 1861: Not many lived to be 90. Will grow quickly b/c majority of people are young and h ave yet to reproduce 2001: More people living to be 90 (majority F) -There are way more people in the older age classes, fewer in younger -Most people are passed reproductive age, not many ppll left that have to reproduce First estimate of human capacity of earth: Antoni van Leewenhoek, 1679 Estimated land area of globe, applied human density of crowded Holland: Room for 13.4 billion Venneer: Calculated land area -> used density data of Holland -> We can fit 13.4 billion p eople! Cohen’s history of K estimates Note log scale: Range over 3 orders of magnitude, 1 billion to 1 trillion -this is a LOG scale. Estimates are ranging from 1 trillion to 1 billion -As of yet, we do not have a firm handle on what the total carrying capacity of t he earth is -Rather than focusing on the absolute K (modelling it, making projection based on age structure)… we should model it based on standard of living Lester Brown: Real answer depends on how pe...
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