Lecture 20: Population Ecology 1
o Population: group of individuals of the same species, living in a defined geographic area
o Populations have various characteristics that are not associated with an individual's
comprising, which include:
Allele frequencies, genotype frequencies
Population size (N)
Rate of growth
Mark-recapture method (population size):
o The most common method to estimate population size
o You go out and capture a sample number of organisms and you place a marking on
them [capture & MARK an initial sample (M)] and let them go
o Later, capture a second sample of animals (C) & see how many have been marked
before: RECAPTURES (R) and use this to estimate population size (N)
Clicker Question: You catch and clip the toes of 100 frogs in a lake. A few days later you return
and capture 75 frogs, 10 with clipped toes. Approximately how many frogs live in the lake?
Mark-recapture works if...
o Marked and unmarked animals have to have equally probability of being captured
o The marks should not affect the survivorship of the animals
o The marks remain relatively permanent (they from the first visit to the second visit)
o The time elapsed between the two visits should be long enough for the marked animals
to get away and mix freely with the unmarked population, but not so long that the
population size changes
Clicker Question: In a mark-release-recapture study of blackbirds, many individuals become 'trap
happy'...after they are caught once, they are very easy to catch again. How will this affect the
estimate of population size?
A. N will be overestimated
B. N will be under estimated
C. This should have no effect.
Clicker Question: Oh No! You foolishly use washable marker to mark the wings of butterflies in a
mark-recapture study. Some marks wash off before the second sample is captured. How will this
affect your estimate of N? A. N will be overestimated
B. N will be underestimated