Measuring Population Size• Census (count EVERYTHING?!?!)• Sampling – Lincoln Index (capture, tag, recapture) – Quadrat (count in a small sample area, apply to entire area)
Lincoln Indexpopulation size = (n1 X n2)/n3where . . .• n1= number of individuals initially caught, marked and released• n2 = total number of individuals caught in the second sample• n3 = number of marked individuals in the second sample
Quadrat Method• Random sampling of plant species usually involves counting numbers in small, randomly located, squares within the total area.• These squares are usually marked with frames called quadrats.
Quadrat Method• Mark out gridlines along two edges of the area• Use a calculator or tables to generate two random numbers to be used as coordinates. Place a quadrat at the coordinatesExample: 14, 31
Quadrat Method1. Count how many individuals are inside the quadrat.2. Repeat steps 2 and 3 as many times as possible.
Quadrat Method1. Measure the total size of the area occupied by the population, in square meters
Quadrat Method1. calculate the mean number of plants per quadrat. Then calculate the population size using the following equation: Population = (quadrat mean X total area) quadrat area