# Sampling Animals

• Created by: Psychie
• Created on: 01-02-15 16:36

## Mark, release, recapture Method.

• Some animals are trapped, e.g. using pitfall traps.
• They are marked in some harmless way then released.
• Traps are used a few days later.
• The number of marked and unmarked animals are recorded.
• The population size is estimated usinf this formula:

Population size:   Number in 1st sample X Number in 2nd sample

Number in 2nd sample previously marked

• E.g. 10 animals were trapped, marked and released. 2 days later, 20 animals were trapped, where 5 were found to be marked:

Population size: 10 X 20  = 200 = 40                                                                                                                           5           5

Assumptions:

• Marked animals will mix with origninal population.
• The marking doesn't affect their survival.
• No deaths and no births - population size stays the same ( stable )
• No movement of animals in and out of the area.
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## Animals that move are tricky to sample

• Move around - could be counted twice.
• A risk of not counting all the animals if they are moving about.
• Some animals may be active at different times of the day.
• Animals ma run away or hide from you as you approach them to sample them.
• You cannot be certain if an animal actually belongs to the habitat you re sampling.

So....

• Large animals can be observed.
• Smaller animals and microbes trapped using appropriate equipment.
• Mark, release ,recapture method can be used to estimate the population.
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