Table 1.

Analysis of molecular variance of B. attramentaria (snail host) and HL1 and HL6 (trematode parasites) in the native and introduced ranges

Region	Species	Source of variation	Df	Percent of variation	ΦST	P value
Native range	B. attramentaria	Among	13	77.45	0.77	<0.0001
		Within	126	22.55
		Total	139
	HL6	Among	12	1.23	0.01	0.12
		Within	163	98.77
		Total	175
	HL1	Among	12	2.29	0.02	0.21
		Within	86	97.71
		Total	98
Introduced range	B. attramentaria	Among	3	0	0.00	1.00
		Within	36	100
		Total	39
	HL6	Among	3	1.04	0.01	0.32
		Within	248	98.96
		Total	251
	HL1	Among	3	−0.90	−0.01	0.73
		Within	127	100.9
		Total	130

Because variance estimates are based on measures of covariance, percent variation can be zero or negative when the actual values are small (37).