Dispersion Analysis

A number of different techniques have been developed to measure the distribution (random, clumped, or even) of individuals. We will use Morista's Index of dispersion (1959) to determine the patterns of dispersion of the species sampled in the plot sampling lab.

The following equation can be used to calculate dispersion of individuals from quadrat (plot) data:

I_d = p X
(n²-N)

_______

N(N-1)
     Equation #1

I_d = index of dispersion

p = number of plots

n = number of individuals in each plot

N = total number of individuals

I_d > 1   Values significantly greater than 1 indicate a clumped distribution.

I_d = 1   Values close to 1 indicate a random distribution.

I_d < 1   Values significantly less than 1 indicate an even (uniform) distribution.

In the example below, we will calculate an index of dispersion for species A. Three plots (samples) were taken. The second row of the table gives the number of individuals of species A.

plot #	# species A	n²
1	3	9
2	5	25
3	0	0
	N = 8	n²= 34

I_d = 3 X

(34-8)

_____

(8 X 7)

= 1.4