Population and sampling

what is a population

a group of organisms of the same species living in an area at one time that are able to interbreed with each other

what happens if a population is isolated

members of seperate populations cannot breed together

what is the result of this

gene exchange cannot take place between them

how do we count the organisms in a population

count a sample from a small area and multiply this by the total area of the habitat

what is sampling

investigating the distribution and abundance of populations

what are the two sampling methods for sessile organisms

• quadrat

• line/belt transect

what does a quadrat do

uses defined areas of space to count the number of species within

what is quadrat sampling

a method used to take a measurement of an area without systematically deciding where to take it

what does quadrat sampling do

eliminate bias

how can random quadrat sampling be used

when working out the population size of a species of stationary animals/plants

what is it only suitable for sampling

sessile organisms like plants or very small moving organisms

the procedure

.

step 1

use a random number generator to determine coordinates within the study area

step 2

use a measuring tape

step 3

place the quadrat at these coordinates OR place it randomly in the a

what is this method only best for

non-motile (sessile) organisms

what are some methods used to collect motile animals

• pitfall traps

• pooters (aspirators)

• mammal traps

• nets

what is the main method that can be used on motile organisms

(capture) mark-release-recapture: MMR

what is another name for the MMR technique

Lincoln index

MMR method

.

MMR step 1

first large sample is taken; caught, counted and marked

what are the organisms marked with

ring, tag, dab of paint or nail varnish

MMR step 2

return the marked individuals to their habitat, mix with the rest of the population

MMR step 3

after time has past, another large sample should be captured

MMR step 4

marked and unmarked individuals are counted

MMR step 5

the proportion of marked to unmarked individuals is used to calculate an estimate of the population size

Formula