Question

1. How would you calculate the population size of a species of plant? How would you calculate the population size of a species of mice?

2. Practice: A biologist originally marked 40 butterflies in a park. Over a period of 30 days, butterfly traps caught 200 butterflies. Of the 200 captured, 8 were found to have tags. Based on this information, what is the estimated population size of the butterflies in the Park?

Answer 1

Plant population size can be estimated by quadrat method. We divide the repreentative area in to quadrats and count the number of organisms of each quadrant. Quadrats uniformly sized and are kept  randomly in the selected areas for sampling. Number of individual plants present in each quadrat are recorded and averaged. This gives per quadrat number of plants.

N= A/a x n

N= total population size.

A= total study area

a = area of the quadrat

n= Average Number of organisms per quadrat

Animal population(mice) size is estimated by mark and recapture method.

A small population of mice is collected and a small mark can be placed on them. After some duration you visit the same place and capture some mice again. Count the total individuals captured second time and also note the recaptured mice (mice with marks on them).

N = Mx C / R

N= population size.

M== total mice marked

C= Total mice captured second time ( with and without marks)

R= number of mice captured with marks (recaptured).

N gives the number of mice in the region by mark-recaptured method.

Practice--

Marked butter flies---40

Total captured butterflies after 30 days---200

Recaptured butterflies---8

So the total population size (N) is -----40 x 200 /8 = 1000

THere are 1000 butterflies in the park.