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Lecture 20

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Western University
Biology 1001A
Tom Haffie

Chapter 45-45.2 (Lecture 20 Population Ecology) Population • Group of individuals of the same species, living in a defined geographic area Characteristics of Populations • Populations have many attributes that are not associated with individuals: o Allele frequencies, genotype frequencies o Population size (N) o Geographic range o Sex Ratio o Age structure o Rate of Growth POPULATION SIZE • Estimating Population Size: Mark-Recapture Method o Capture and Mark an initial sample (M) o Later, capture a second sample of animals (C) and see how many are already marked (R) o Use this to estimate population size (N) MC N= R • Mark-Recapture works if: o Marked and unmarked animals equally likely to be captured o Marks don’t affect survival rate o Marks don’t wear off o Time between two samples is long enough for marked animals to mix freely with unmarked animals, but not so long that population size changes POPULATION DENSITY • Number of organisms per unit area Density= N Area • Why does density matter? o Influences access to resources o Density too high: per capita growth rate (rate of increase per individual per unit time, r) may decrease o Density too low: per
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