# Mark and Recapture

Mark and Recapture

A Method of Population Estimation

How it works:

• Capture and Mark a number of individuals in a natural population.

• Return them to that population.

• After “awhile”, capture/recapture individuals in that same population as a basis to estimate population size.

Lincoln-Peterson Index

• If a proportion of a population was captured, marked, returned to the population, and a second sample was taken; the proportion of individuals marked in the second sample would be the same as was marked initially in the total population!

Example (previous slide)

Marked Initially

----------------------------

Total Population Size

12 4

----- = -------

X 15

• X = 43

Marked Recaptured

= -----------------------------

Total in Second Sample

Assumptions…

• 1. Nothing has happened to the natural population between capture and recapture.

• 2. Chances for being captured are equal for all individuals.

• 3. Sufficient time between capture and recapture for adequate “mixing” back into the population.

• 4. Animals don’t lose their marks.

• Random

Population Dispersion

• clumped

• uniform

Population density

• Comparing Population Density

Population Density = Number of people/unit area

• Example: North Carolina has 9,900,000 people living in 139,390 km2. What’s the population density?

• country population area (km2)

• Nigeria 173,600,000 923,768

• United States 313,900,000 9,827,000

• China

• Haiti

• India

1,350,000,000 9,707,000

10,200,000 27,750

• Russia