Lecture 19 - BIO220

this is in contrast to fisherybird population island

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Unformatted text preview: le -As time goes on, the exponent r becomes larger and larger! -This is in contrast to fishery/bird population island models. Those models are density dependent. High D = Slow Growth Exponential growth cannot continue unchecked, so more complex models are needed • Simplest model of density dependent regulation is the logistic: dN dt K N K • Allee, Emerson, Park, Park & Schmidt (1949), “The Great APPES” Sigmoid growth, asymptotic approach to carrying capacity (K) 20th In mid century, logistic model was viewed almost as an ecological law… rN Historical perspective from first really successful ecology textbook: N Time -This logistic curve is representative of what happens in natural p opulations when they are growing in DENSITY DEPENDENT fashions -Similar to bird populations etc. 1 20/03/2013 Human projection from Allee et al. in 1940’s So, how did this prediction do? 2011: 7 billion and climbing! Best fit of logistic equation to data suggests leveling off at 2.6 billion -Assuming that the population was growing LOGISTICALLY, the upper estimate was: 2.6 BILLION Extrapolating from logistic gave a very poor prediction…why? * So far, human population growth looks much more like exponential growth than logistic. * -Our growth illustrates density INDEPENDENT growth! Are we experiencing an overshoot due to delayed response? Or is K changing? • Statistical – Extrapolating beyond the range of data is always dangerous – Logistic is not a law, just a very simple possible hypothesis for density dependence • Biological – Logistic allows no overshoots – Logistic assumes r and K to be constants -r and K will not always be constant: technology incre...
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This document was uploaded on 01/27/2014.

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