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Lecture 20

Biology 1001A - Lecture 20.docx

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Biology 1001A
Tom Haffie

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Biology 1001A Lecture 20: Population Ecology I November 21, 2011 Read: Sections 45.3-45.5 Recap: Virulence and Transmission Mode  Transmission Mode Hypothesis: o Optimal virulence depends on how the parasite moves between host individuals Practical Implications  Reduce chances for indirect transmission  parasites rely more on direct transmission  promotes evolution of reduced virulence. o Ex. Mosquito Net prevents malaria Population Ecology  Population: o Group of individuals of the same species, living in a defined geographic area  Characteristics: o Populations have attributes that are not associated with individuals:  Allele frequencies, genotype frequencies  Population Size (N)  Geographic Range  Sex Ratio  Age Structure  Rate of Growth Population Size  How to estimate population size? o Mark-Recapture Method  (First visit) Capture & MARK an initial sample (M)  (Second Visit) CAPTURE a second sample of animals (C) and see how many are marked RECAPTURES (R)  Use this to estimate population sixe (N)  R/C = M/N  N = MC/R  Mark-recapture works if…  Marked and unmarked animals equally likely to be captured  Marks don’t affect survival  Marks don’t wear off  Time between 2 samples is long enough for marked animals to mix freely with unmarked animals, but no so ling that population size changes Population Density  Density = N/Area o or Density = N/Volume o Density is higher for animals with smaller body size o Density is lower for animals with larger body size  Why does density matter? o Influences access to resources o Density too high:  Per capita growth rate (rate of increase per individual per unit
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