308 
PACIFIC SCIENCE, Vol. XV, April 1961 
TABLE 1 
Data Comparing Various Fresh Water 
Habitats in the Bellingham, Washington, 
Area Using the Species Commonality Index 
(SCI) 
COMBINATION 
TOTAL NO. 
SPECIES 
NO. SPECIES 
IN COMMON 
SCI 
Whatcom Rapids 
Lake Fragrance 
28 
5 
17 
Good Pond 
Bad Pond 
24 
8 
33 
Bad Pond 
Peat Bog 
18 
9 
50 
Good Pond 
Peat Bog 
19 
6 
32 
Lake Fragrance 
Good Pond 
22 
12 
55 
Lake Fragrance 
Bad Pond 
24 
8 
33 
Lake Fragrance 
Peat Bog 
23 
' 7 
30 
Whatcom Rapids 
Mud Lake 
28 
11 
39 
Whatcom Pools 
Good Pond 
23 
8 
35 
Whatcom Pools 
Bad Pond 
21 
8 
38 
Whatcom Pools 
Peat Bog 
21 
8 
38 
Whatcom Rapids 
Good Pond 
26 
5 
19 
Whatcom Rapids 
Bad Pond 
24 
4 
16 
Whatcom Rapids 
Peat Bog 
22 
4 
18 
Fragrance Lake 
Mud Lake 
24 
10 
42 
Mud Lake 
Good Pond 
24 
9 
37 
Mud Lake 
Bad Pond 
25 
7 ' 
28 
Mud Lake 
Peat Bog 
24 
7 
29 
Whatcom Pools 
Whatcom Rapids 
24 
9 
. 38 
Whatcom Pools 
Lake Fragrance 
28 
6 
21 
Whatcom Pools 
Mud Lake 
27 
6 
22 
common to fishermen in the locality, that trout 
stocking is much more successful in Good Pond 
than in Bad Pond — thus the names for the two 
ponds. 
It should be emphasized that the method is 
useful only if: 
1. Thorough and complete collections are 
made. It is obvious that the greater the number 
of species in common, the greater the similarity 
of niches, and the more similar the physical 
attributes to account for the species similarity. 
Thus, the more thorough the collection, the 
more valid the results. 
2. The collections are made as concurrently as 
possible. This prevents seasonal variation from 
giving too low an index. If an index is desired 
which covers a longer period, then of course 
concurrent collections should be made over sev- 
eral seasons. 
3. Statements such as, "Mud Lake and Bad 
Pond are twice as dissimilar as are Lake Fra- 
grance and Good Pond,” are unwarranted. It is 
certainly possible to have a zero SCI but for 
the habitats to have many similarities. 
4. The method is applied within limited areas 
where biotic communication between habitats is 
constantly possible and likely. For example, it 
would be unrealistic to compare a pond in New 
Zealand with one in Washington by this 
method. Even though the physical attributes of 
the habitats might be very similar, there is no 
chance of obtaining a high index. 
It is the writer’s intention in the future to 
make more thorough collections of these same 
areas and of others, and to attempt relating the 
various indexes to the physical characteristics of 
the habitats . — Charles J. Flora , Department of 
Biology, Western Washington College of Educa- 
tion, Bellingham, Washington. 
