Table 3.

ANCOVA statistics for the variation in overall trematode prevalence in Radix auricularia and the prevalence of infection of the two major transmission guilds as a function of lake, season and year and their interactions.

Variable	Factor	ANCOVA 1			ANCOVA 2
		3 lakes and 3 seasons			3 lakes and 2 seasons
		df	F	P	df	F	P
Overall prevalence	Lake	2, 33	1.51	ns	2, 30	1.80	ns
	Season	2, 33	0.79	ns	1, 30	0.03	ns
	Lake and season	4, 33	0.36	ns	2, 30	0.55	ns
	Lake	2, 36	2.57	ns	2, 30	1.99	ns
	Year	1, 36	2.69	ns	1, 30	1.21	ns
	Lake and year	2, 36	1.58	ns	2, 30	0.98	ns
	Season	—	—	—	1, 32	0.16	ns
	Year	—	—	—	1, 32	2.31	ns
	Season and year	—	—	—	1, 32	1.96	ns
Waterfowl guild prevalence	Lake	2, 33	4.06	<0.05	2, 30	6.13	<0.01
	Season	2, 33	0.36	ns	1, 30	0.53	ns
	Lake and season	4, 33	3.19	<0.05	2, 30	2.76	ns
	Lake	2, 36	6.61	<0.01	2, 30	12.36	<0.001
	Year	1, 36	2.58	ns	1, 30	3.76	ns
	Lake and year	2, 36	0.26	ns	2, 30	1.85	ns
	Season	—	—	—	1, 32	0.07	ns
	Year	—	—	—	1, 32	4.23	0.048*
	Season and year	—	—	—	1, 32	0.27	ns
Fish-eating bird guild prevalence	Lake	2, 33	0.69	ns	2, 30	0.81	ns
	Season	2, 33	1.96	ns	1, 30	0.29	ns
	Lake and season	4, 33	1.88	ns	2, 30	3.39	0.047*
	Lake	2, 36	0.35	ns	2, 30	0.06	ns
	Year	1, 36	5.34	<0.05	1, 30	2.97	ns
	Lake and year	2, 36	1.41	ns	2, 30	1.38	ns
	Season	—	—	—	1, 32	1.13	ns
	Year	—	—	—	1, 32	7.22	<0.05
	Season and year	—	—	—	1, 32	3.42	ns

^*No differences detected in post-hoc Tukey’s test.

Abbreviation: ns = not significant.