84

Community Analysis Package

where the number of species present in both samples is a, the number of species

present in sample 1 but missing from sample 2 is b, the number of species

missing in sample 1 but present in sample 2 is c and the number of species

missing from both samples is d. The total number of species, N, is therefore

a+b+c+d.

This measure is:

(

a

 + 

d

)/(

a

 + 2

b

 + 2

c

 + 

d

)

17.3

S3

For measures of similarity between samples based on species presence absence

the observations can be summarised in a simple frequency table:

Sam

Species Present

Sample 2

Species Present

a

Species  Absent

c

where the number of species present in both samples is a, the number of species

present in sample 1 but missing from sample 2 is b, the number of species

missing in sample 1 but present in sample 2 is c and the number of species

missing from both samples is d. The total number of species, N, is therefore

a+b+c+d.

This measure is:

17.4

S4

For measures of similarity between samples based on species presence absence

the observations can be summarised in a simple frequency table:

Sam

Species Present

Sample 2

Species Present

a

Species  Absent

c

where the number of species present in both samples is a, the number of species

present in sample 1 but missing from sample 2 is b, the number of species

missing in sample 1 but present in sample 2 is c and the number of species

missing from both samples is d. The total number of species, N, is therefore

a+b+c+d.

This measure is:

(a + d) / (b + c)

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