Similarity measures

89

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:

17.14 Ochiai

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:

17.15 Q1

This is simply the agreement (number of species which have the same

abundance in the two samples) divided  by the total number of species.

Example:  Ten species at two sites:

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